Drainage and Drying of Small Gaps in Wall Systems

Drainage and Drying of
Small Gaps in Wall Systems
by
Jonathan Smegal
A thesis
presented to the University of Waterloo
in fulfillment of the
thesis requirement for the degree of
Master of Applied Science
in
Civil Engineering
Waterloo, Ontario, Canada, 2006
© Jonathan Smegal, 2006
I hereby declare that I am the sole author of this thesis.
I authorize the University of Waterloo to lend this thesis to other institutions or individuals for the
purpose of scholarly research
Signature
I further authorize the University of Waterloo to reproduce this thesis by photocopying or by other
means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly
research.
Signature
ii
Abstract
Drainage and Drying of Small Gaps in Wall Systems
There are many references to the benefits of a drainage gap behind claddings to manage
water, but very few specific details for the requirements of the drainage gap. Much research
has been done in the areas of materials testing and driving rain since driving rain is the
largest contributor to building enclosure wetting and premature enclosure failure. However,
very little work has been carried out on the performance of drainage gaps for both drainage
and ventilation drying as well as the storage capacities of different wall systems.
The main objectives of this study are to gain a better understanding of drainage and drying
in the small gaps behind claddings, as well as to develop a repeatable and representative test
method to characterize different cladding systems.
A theoretical analysis was undertaken for drainage cavities calculating the maximum and
minimum flow rates through drainage cavities using the modified Darcy Weisbach equation.
Driving rain data for Canada from previous research was coupled with a water ingress
study by the National Research Council (NRC) to help predict quantities of water that could
enter the drainage cavity in certain climatic regions.
It was found that standard test
application rates and pressures (from ASTM and CSA) are orders of magnitude higher than
driving rain and wind pressures during most rain events. Based on the driving rain and
leakage study, it was concluded that the number of variables contributing to water leakage
make the predicted range of leakage rates vary over two orders of magnitude.
A test was developed and used to investigate several commonly used cladding materials
including EIFS, Stucco, and various siding products. These claddings were installed over
various sheathing membranes including, housewrap, building paper, trowel applied barriers,
and air gap membranes. A range of different materials were used to better understand the
performance of the claddings and weather resistant barriers in different wall systems. A
series of baseline values for storage and drying were found using non absorptive materials.
iii
The experimental results found during testing for drainage and drying can be used for
hygrothermal modeling of wall performance.
It was found that even a small gap (less than 1 mm) will drain considerably more water
than is expected to penetrate most walls. For example, a gap that is 0.5mm can easily drain 1
litre/minute-meter width.
The drainage test method and apparatus generated repeatable results in the lab under the
same conditions, and was also repeatable on similar walls in two different locations on two
different apparatuses.
Ventilation drying was shown to be effective even in small gaps (1mm). Ventilation
drying is more effective with increases in gap width, but it is unclear when the optimum gap
has been reached for ventilation drying above which no improvements in drying are
achieved.
To build on knowledge gained in this thesis more investigation is needed to analyze the
surface contact angles, and moisture stored on non absorptive surfaces. It was shown that
ventilation is important for drying in air spaces but a more detailed analysis of ventilation
drying should be conducted to determine the optimum gap width for ventilation drying.
Non absorptive enclosure materials behaved much more predictably during storage and
drying than similar walls with absorptive materials. Further analysis may reveal methods to
more accurately predict the performance of absorptive wall system materials.
It was shown that some test standards and performance design criteria were very
unrealistic for testing.
These test standards and performance specifications should be
designed to simulate realistic loadings and performance.
iv
Acknowledgements
I would like to thank Dr. John Straube for giving me the opportunity to change engineering
disciplines and complete my thesis in building science which I truly enjoy. He gave me the
freedom to work at my own pace and schedule while giving me the opportunity to learn as
much about other areas of building science as I wanted to. His enthusiasm for building
science is truly contagious.
I would also like to thank the rest of the building engineering group for always have an
opinion and insight to my research problems. In particular I would like to thank Mr. Chris
Schumacher whose knowledge and experience helped this research start in the right direction
with the testing apparatus.
Thanks to all my friends and family who supported me through this work some of whom
thought I may never finish.
Thank you also to several building products manufacturers for materials or funding,
including James Hardie Building Products, Cosella Doerken, Louisiana Pacific, Icon
Building Products, Sto, and Dupont.
v
Table of Contents
Abstract ................................................................................................................................................. iii
Acknowledgements................................................................................................................................ v
Table of Contents.................................................................................................................................. vi
List of Figures ..................................................................................................................................... viii
List of Tables ......................................................................................................................................... x
1.0
Introduction................................................................................................................................ 1
1.1
Background ............................................................................................................................ 1
1.2
Objective ................................................................................................................................ 3
1.3
Approach................................................................................................................................ 3
2.0
The Building Enclosure ............................................................................................................. 5
2.1
Building Enclosure Functions................................................................................................ 5
2.2
Building Enclosure History.................................................................................................... 6
3.0
Moisture Physics ...................................................................................................................... 11
3.1
Psychrometrics: Moisture in Air .......................................................................................... 11
3.1.1
Psychrometric Examples.............................................................................................. 13
3.2
Moisture in Materials ........................................................................................................... 15
3.3
Moisture in Assemblies........................................................................................................ 18
3.4
Moisture Movement............................................................................................................. 19
3.4.1
Capillarity .................................................................................................................... 19
3.4.2
Gravity ......................................................................................................................... 21
3.4.3
Air Movement .............................................................................................................. 21
3.4.4
Diffusion ...................................................................................................................... 22
3.5
Wetting................................................................................................................................. 22
3.6
Drying .................................................................................................................................. 23
3.6.1
Wind............................................................................................................................. 24
4.0
Rain Control Strategies ............................................................................................................ 26
4.1.1
Deflection..................................................................................................................... 26
4.1.2
Drainage, Exclusion, Storage....................................................................................... 28
4.1.3
Drying .......................................................................................................................... 32
5.0
Research Program .................................................................................................................... 33
5.1
Objectives ............................................................................................................................ 33
5.2
Approach.............................................................................................................................. 33
6.0
Drainage Gap Analysis ............................................................................................................ 35
6.1
Assumptions......................................................................................................................... 35
6.2
Theoretical Maximum Flowrate........................................................................................... 35
6.3
Theoretical Minimum Flowrate ........................................................................................... 42
6.4
Conclusions.......................................................................................................................... 43
7.0
Analysis of Drainage Loads..................................................................................................... 44
7.1
Development of Driving Rain Analysis............................................................................... 44
7.2
Case Study ........................................................................................................................... 47
7.2.1
Building Design Deficiencies ...................................................................................... 47
7.2.2
Calculating Driving Rain ............................................................................................. 48
7.2.3
Water Ingress ............................................................................................................... 55
7.3
Conclusions.......................................................................................................................... 59
8.0
Drainage and Drying Test Development.................................................................................. 60
8.1
Test Standards ...................................................................................................................... 60
vi
8.2
Previous Test Methods ......................................................................................................... 62
8.3
Test Development................................................................................................................. 65
8.3.1
Plexiglas and Polyethylene Sheet Testing .................................................................... 73
8.4
Conclusions .......................................................................................................................... 76
9.0
Drainage and Drying Test Program.......................................................................................... 77
9.1
Test program......................................................................................................................... 77
9.2
Drainage and Drying Results – Continuous Drainage Gap .................................................. 79
9.2.1
EIFS Testing................................................................................................................. 79
9.2.2
Grooved EIFS Testing .................................................................................................. 85
9.2.3
Stucco Wall Testing ..................................................................................................... 86
9.2.4
Fiber Cement Sheet Testing ......................................................................................... 88
9.2.5
Air Gap Membrane Testing.......................................................................................... 92
9.2.6
Flow visualization ........................................................................................................ 96
9.3
Drainage and Drying Results – Discontinuous Drainage Gaps............................................ 98
9.3.1
Vinyl Siding.................................................................................................................. 99
9.3.2
Fiber Cement Plank .................................................................................................... 103
9.3.3
Louisiana Pacific Smartside ....................................................................................... 109
9.3.4
Cedar Siding ............................................................................................................... 110
9.4
Analysis of Results ............................................................................................................. 112
10.0 Conclusions ............................................................................................................................ 114
11.0 References .............................................................................................................................. 118
Appendix A Airflow Testing.............................................................................................................. 121
Air Flow Tests .................................................................................................................................... 122
Intent............................................................................................................................................... 122
Set up.............................................................................................................................................. 122
Appendix B Wall Construction Specifications................................................................................... 127
vii
List of Figures
Figure 2-1 : Functions of the Building Enclosure (Straube and Burnett, 2005) .................................... 5
Figure 2-2 : Mesa Verde Colorado ........................................................................................................ 7
Figure 2-3 : Adobe Construction in New Mexico.................................................................................. 8
Figure 3-1 : Simplified Pyschrometric Chart ....................................................................................... 12
Figure 3-2 : Practical Examples using the Psychrometric Chart.......................................................... 14
Figure 3-3 : Components of a sorption isotherm for a hygroscopic material (Straube and Burnett
2005) .................................................................................................................................................... 16
Figure 3-4 : Sorption isotherms of various materials (Hutcheon and Handegord 1995) ..................... 17
Figure 3-5 : Moisture Storage in Wall Assemblies (Straube and Burnett 2005) ................................. 18
Figure 3-6 : Capillary suction of water in a tube (Straube and Burnett 2005)..................................... 19
Figure 3-7 : Contact Angles ................................................................................................................. 21
Figure 3-8 : Drying Mechanisms for Wall Systems............................................................................. 24
Figure 3-9 : Ventilation of Directly Applied Siding (Van Straaten 2005)........................................... 25
Figure 4-1 : Correlation of Overhang Size on Low Rise Buildings and Wall Problems Due to Water in
Vancouver, B.C. (Morrison-Hershfield 1997) ..................................................................................... 27
Figure 4-2 : Driving Rain Roses for Toronto and Vancouver (Straube and Schumacher 2005) ......... 28
Figure 4-3 : Rain Control Stategies in Wall Systems (Straube and Burnett 2005) .............................. 29
Figure 4-4 : Requirements for Drained Wall System (Straube and Burnett 2005) .............................. 31
Figure 6-1 : Comparison of Actual Hydraulic Diameter (equation 4.2) to Simplified Hydraulic
Diameter (equation 4.3) ....................................................................................................................... 37
Figure 6-2 : Case I and II for Drainage Analysis (Note: R.O.W. = Rest Of Wall).............................. 39
Figure 6-3 : Case I Drainage Analysis ................................................................................................. 40
Figure 6-4 : Case II Drainage Analysis................................................................................................ 41
Figure 6-5 : Capillary Rise in a Gap Between Plates For Different Contact Angles ........................... 43
Figure 7-1 : Estimated RDF values (Straube and Burnett 2005) ......................................................... 46
Figure 7-2 : Theoretical Building and Deficiency Locations............................................................... 47
Figure 7-3 : Total Average Annual Driving Rain in the Worst Wall (Straube and Schumacher 2005)49
Figure 7-4 : Driving Rain Analysis of 42 Canadian Cities .................................................................. 50
Figure 7-5 : Extreme Driving Rain Events from Canadian Weather Data........................................... 51
Figure 7-6 : Probability of Wind Pressures During Rain Events > 5.1 mm/hr .................................... 52
Figure 7-7 : Wind velocity variation with height and location (Straube and Burnett 2005)................ 55
Figure 7-8 : Location of Design Deficiencies (Lacasse et al. 2003) .................................................... 56
Figure 7-9 : Water Entry Rates and Spray Rate at Different Pressures (Lacasse et al. 2003) ............. 58
Figure 8-1 : Test Apparatus for Ventilation Drying Study (Schumacher et al. 2003) ......................... 63
Figure 8-2 : Test Results for Ventilation Drying Study (Shumacher et al. 2003)................................ 64
Figure 8-3 : Testing Apparatus ............................................................................................................ 67
Figure 8-4 : Photograph of Testing Apparatus..................................................................................... 68
Figure 8-5 : Test Wall Construction .................................................................................................... 69
Figure 8-6 : Commissioning Test Results............................................................................................ 70
Figure 8-7 : Comparison of Drying With and Without Polyisocyanurate Sealing the Studspace ....... 71
Figure 8-8 : Comparison of Drying With and Without Simulated Wind Pressure .............................. 72
Figure 8-9 : Effects on Testing from Changes in Laboratory RH........................................................ 73
Figure 8-10 : Effect of Fan on Drying of Plexiglas Wall System ........................................................ 75
Figure 9-1 : EIFS Wall Drawings ........................................................................................................ 81
Figure 9-2 : Repeatability of Drying Results ....................................................................................... 82
Figure 9-3 : Drainage Patterns in EIFS-5 Wall................................................................................... 84
viii
Figure 9-4 : Drainage Gap of Grooved EIFS Wall Panel..................................................................... 85
Figure 9-5 : Stucco Wall System Construction ................................................................................... 86
Figure 9-6 : Comparison of Drying for Stucco-1 and Stucco-2 ........................................................... 87
Figure 9-7 : New Zealand Style Construction with no Sheathing ........................................................ 88
Figure 9-8 : Drainage Test Results for Various Size Test Walls in Waterloo and Fontana ................. 90
Figure 9-9 : Leaking Housewrap ......................................................................................................... 91
Figure 9-10 : Comparison of Cladding................................................................................................. 92
Figure 9-11 : Air Gap Membrane Test Drawings................................................................................. 93
Figure 9-12 : Results for AGM-1 Drying Tests ................................................................................... 94
Figure 9-13 : Results of Felt Drying Tests (Felt 3 and 4)..................................................................... 95
Figure 9-14 : Comparison of Flow Pattern for Point Source Load....................................................... 97
Figure 9-15 : Comparison of Flow Pattern for a Distributed Load ..................................................... 98
Figure 9-16 : Vinyl Siding Wall Test ................................................................................................... 99
Figure 9-17 : Drainage Test Results for Vinyl Siding on Tyvek....................................................... 101
Figure 9-18 : Drying Curves for Vinyl Siding over Tyvek Using Different Drying Techniques ...... 102
Figure 9-19 : Drying Curves for Vinyl over #15 felt Using Different Drying Techniques................ 102
Figure 9-20 : Drying Test for Fiber Cement Board Not at Equilibrium with Laboratory.................. 105
Figure 9-21 : Attempting to Reach Maximum Storage in Fiber Cement plank ................................. 106
Figure 9-22 : Analysis of Drainage Patterns on Clapboard Siding .................................................... 107
Figure 9-23 : Visual Inspection of the Back of Fiber Cement............................................................ 108
Figure 9-24 : Drying Curves for Fiber Cement Cladding Walls With #15 Felt Paper ....................... 109
Figure 9-25 : Drying Comparison of Cedar Siding Testing .............................................................. 111
ix
List of Tables
Table 6-1 : Case I flow velocity and rate as a function of gap width................................................... 39
Table 7-1 : Deficiency Descriptions .................................................................................................... 48
Table 7-2 : Driving Rain Amounts for Case Study.............................................................................. 51
Table 7-3 : Water penetration testing standards (Lacasse et al. 2003)................................................. 53
Table 7-4 : Wind speed location constants .......................................................................................... 54
Table 7-5 : Maximum water entry L/min at Different Points of Collection (Lacasse et al. 2003) ...... 57
Table 8-1 :Comparison of Test Standards to Calculated Rain Loads .................................................. 61
Table 8-2 : Results of Drainage and Storage Testing on a Plexiglas Wall System.............................. 74
Table 9-1 : Test Matrix for Continuous Drainage Gap Assemblies.................................................... 78
Table 9-2 : Test Matrix for Discontinuous Drainage Gap Assemblies ................................................ 79
Table 9-3 : Results from EIFS Drainage Testing................................................................................. 80
Table 9-4 : Drainage Test Results of Grooved EIFS Panel ................................................................. 86
Table 9-5 : Drainage Test Results of Stucco Wall System .................................................................. 87
Table 9-6 : Fiber Cement Sheet Testing at Different Locations .......................................................... 89
Table 9-7 : Drainage Results for Air Gap Membrane Testing............................................................. 93
Table 9-8 : Drainage Testing Results of Vinyl Siding Wall System ................................................ 100
Table 9-9 : Test Matrix for Fiber Cement Testing............................................................................. 103
Table 9-10 : Drainage Test Data for Fiber Cement Maximum Storage Test ..................................... 106
Table 9-11 : Test Matrix for LP Smartside Testing ........................................................................... 110
Table 9-12 : Test Matrix for Cedar Siding Testing............................................................................ 111
x
1.0 Introduction
1.1
Background
Buildings are an integral part of everyday life since we spend the majority of our time indoors.
Buildings have a great influence over how we live and work. Our productivity and quality of life
is a function of building performance and the environment that they provide. The building
enclosure, defined as the part of the building which separates the interior conditions from the
exterior conditions (Straube and Burnett 2005), is the part of the building most important to the
longevity and durability of any building. Interior conditions are controlled passively by the
building enclosure and actively by the heating, ventilation, and air conditioning (HVAC) system.
These systems have evolved to maintain a comfortable interior environment in most modern
buildings. However, moisture problems in enclosures continue to be a major durability and
indoor environment quality issue for buildings for many reasons.
Poor moisture control in building enclosures can cause many problems ranging from aesthetic
issues such as cladding staining to serious structural degradation such as rotting wood and
corroding steel studs. Mould and fungi are also caused by moisture, with certain occupant health
implications that, although currently not well understood, are detrimental.
Controlling moisture is a balance of wetting and drying. Moisture can enter an enclosure from
several different sources. One source of moisture is built in construction moisture from either
building with green lumber or using materials that were wetted during construction. Other
important moisture sources are precipitation, airborne water vapour and groundwater. All of
these moisture problems can be avoided if the enclosure is well designed, but problems could
still occur due to deficient design details, lack of knowledge, and/or carelessness. Even if the
enclosure is wetted, damage may not occur if the drying is sufficient such that the storage
capacity of the materials is not overcome. Therefore, it is important to design enclosure walls
that are capable of drying.
In the past, buildings were built very differently than today. The building material of choice
was masonry because of its exceptional durability and the flexibility it allowed in design. Other
1
popular materials were stone and solid wood because of local availability. As buildings required
faster construction and local raw materials became less available, materials changed from solid
wood and earth to wood products such as engineered wood, synthetic stucco, and paperfaced
drywall, all of which are generally less moisture tolerant than the materials they replaced. The
majority of houses are built by a relatively small number of large scale builders and due to tight
budgets and short timelines, wet materials and foundations are not provided with adequate drying
periods.
Buildings were constructed with little or no insulation in the past.
Enclosures of these
buildings performed well from a moisture perspective because heat from the interior warmed the
enclosure, which helped dry out any moisture, and decreased the prevalence of freeze thaw
cycling.
After the 1970s oil embargo, insulation and air tightening were employed to reduce
petroleum use for space heating.
By air tightening and insulating buildings, wetting was
increased, and drying was reduced, leading to durability issues. The application of insulation
inhibited drying processes and reduced exterior enclosure temperatures increasing the
occurrences of freeze thaw damage. If the air barrier was not perfect, leaking interior air (now
moist because overall infiltration of dry winter air was reduced) could be concentrated in one
part of the enclosure, and large quantities of water vapour could condense within the enclosure
assembly.
Various design strategies have been employed to control enclosure moisture.
Rain control
strategies, and in particular rainscreen claddings will be explained and examined in detail in the
following sections. This thesis will explore both positive and negative issues of the enclosure
wall systems, and will focus on mechanisms involved in the rainscreen approach.
The rainscreen approach is used to describe wall systems that are constructed with a cladding
that acts as a screen to sun and rain, a second layer, the drainage plane that provides drainage of
water, and a gap between the two to allow drainage leading to flashing and weep holes.
Very little research has been done examining how exterior claddings work as a system
consisting of the cladding, drainage plane, sheathing membrane and framing. The testing for this
thesis used wall systems with these components. Most product manufacturers will perform
2
materials testing on their product but seldom as an entire wall system. Other wall components
may significantly change the predicted performance of a wall system. Examples of this can be
seen in the performance differences of stucco with and without a bond break as well as water
penetration problems with certain types of house wrap. These problems are caused by chemical
and physical interactions between wall components.
1.2
Objective
The main objectives of this study are to gain a better understanding of drainage and drying in
the small gaps behind claddings, as well as to develop a repeatable and representative test
method to characterize different cladding systems. The test method developed will be used to
classify and characterize several different common cladding systems.
1.3
Approach
All available and relevant literature on drainage and drying testing was reviewed. There have
been very few tests done on wall systems in a quantitative manner.
For this reason,
comprehensive surveys of related topics such as driving rain, water ingress, and building
envelope design were completed.
A historical review of buildings and the building enclosure was undertaken and common past
building materials and strategies were investigated. The intent was to explain why old buildings
have lasted so long, and why, “they don’t build them like they used to”.
Attempting to understand the drainage in wall cavities required some research about fluid flow
in cavities. A theoretical analysis was undertaken for drainage cavities calculating the maximum
and minimum flow rates using the modified Darcy Weisbach equation.
Understanding moisture physics is important to understanding drainage in wall cavities.
Forces that move moisture, and moisture storage mechanisms are discussed. Any water that
enters a wall is either stored in the wall components or drained through the wall. The drying
rates for stored moisture are dependant on material properties as well as driving forces such as
3
wind and sun. The test walls were either dried with simulated sun, wind, or with no external
forces.
Driving rain data for Canada was examined from a Canada Mortgage and Housing
Corporation (CMHC) report and coupled with a water ingress study by the National Research
Council (NRC) to help predict quantities of water that could enter the drainage cavity in certain
climatic regions. Estimating how much water enters a rainscreen wall system in various climates
could provide some guidance to developing a realistic test.
A test was developed and used to investigate several commonly used cladding materials
including EIFS, Stucco, and various siding products.
These claddings were installed over
various weather resistant barriers including, housewrap, building paper, trowel applied barriers,
and air gap membranes. Combinations of testing materials were used to better understand the
performance of the claddings and weather resistant barriers in different wall systems. A series of
baseline values for storage and drying were found using non absorptive materials.
These tested wall systems were characterized and classified based on their drainage, storage
and drying characteristics. The results from drainage and drying testing of different wall systems
can be used to advance hygrothermal modeling of different wall system performance. The final
chapter presents the conclusions of the research and testing and makes some recommendations
based on the findings for future work.
4
2.0 The Building Enclosure
The building enclosure is defined as the part of any building that physically separates the
exterior environment from the interior environment. The list of functions for any building is
long and varied as shown by Allen (2005), but the functions for the building enclosure are more
specific. Hutcheon (1963) compiled a list of eleven enclosure requirements which were
subsequently reclassified into three main functions by Straube and Burnett (2005): control,
support, and finish (Figure 2-1). The building function of service distribution also impacts
enclosure performance and design.
Figure 2-1 : Functions of the Building Enclosure (Straube and Burnett, 2005)
2.1
Building Enclosure Functions
The building enclosure should be designed to control the flow of many aspects of the interior
and exterior environments including but not limited to water, air, vapour, insects, noise and solar
radiation. Some of the aspects, like noise, relate entirely to comfort, but other aspects can affect
the durability of a building and lead to premature building failure.
5
The enclosure must resist and transfer all structural loadings from the exterior and interior
environments as well as the enclosure itself. The enclosure does not always resist the gravity
loads from the floor system, but is always connected to the primary structure so the specific
loads on the enclosure will differ between buildings. Another important loading (Hutcheon 1963)
are the induced loads from dimensional changes due to either temperature fluctuations or
changes in moisture content.
The finish of the enclosure should be aesthetically appealing on both the interior and exterior.
The finish should be chosen appropriately for the climate area so that minimum maintenance is
required. Different finishes should be chosen according to the use of the building, so the
building will be functional, and last the desired length of time.
A function of the building, rather than the enclosure, is to distribute services. In many
instances this function interferes with the performance of the enclosure. All of the services will
enter through the enclosure and some may use the enclosure to travel to different areas of the
building. This function will not be discussed in detail in this study but some service penetrations
will be tested in the water ingress study reported later.
2.2
Building Enclosure History
One of man’s basic instincts is to find shelter and this was generally done by choosing sites for
their sheltering qualities, orientation, and useful topography (Allen 2005). In Mesa Verde,
Colorado there is evidence of inhabitants for twelve to fourteen thousand years in the eroded
sandstone cliffs (Knowles 1974). The cliffs provided protection from attacks but also blocked
the high summer sun while allowing low angle winter solar radiation to pass. (Figure 2-2)
This is an early form of passive solar heating, but as populations increased we have neglected
to use the benefits of passive heating as humans did thousands of years ago.
As populations increased and technology advanced, people stopped designing communities in
harmony with nature. Exposed locations meant that the buildings were subject to all of the
meteorological influences. Acoma Pueblo, New Mexico is a good example of early North
American settlement and appears to have been occupied continuously for over a thousand years
6
(Knowles 1974). It was built on a 400 foot high mesa for protection and the houses were made
with adobe covered rubble or adobe covered brick (Figure 2-3).
Figure 2-2 : Mesa Verde Colorado
Adobe is a popular building material in the South West because earth is available, and it
performs well. The thermal properties of adobe allow it to become heated all day, and slowly
radiate heat as the temperature drops overnight. Overhangs on buildings are important for rain
control and will be discussed further in Section 2.3, but in locations such as New Mexico, it
seldom rains, so buildings can perform adequately without overhangs. Because of the dry
climate in the South West, it is not uncommon to construct buildings without overhangs even
today. These buildings were constructed with a great deal of thought towards functionality and
climate, protection from weather and from people.
As technology improved, societies moved from the use of reed and mud bricks to
manufactured fired clay bricks. Bricks allowed a great deal of flexibility in design since they
were small and could be oriented in different directions. They were also quite strong so it was
possible to make larger structures than were previously built. Walls were made multiple bricks
7
thick, depending on the structural load required and the increased wall thickness also increased
the insulative value of the walls.
Figure 2-3 : Adobe Construction in New Mexico
These walls performed reasonably well from a moisture management perspective because
masonry units such as bricks can store a large amount of moisture, and moisture would seldom
reach the interior surface of the enclosure. Also, since there was no insulation, the interior
temperatures would warm the wall, assisting with drying, and keeping the exterior surface
temperature elevated compared to the external temperatures decreasing the chance of freeze thaw
damage. The masonry walls were capable of storing solar energy similar to the adobe walls of
the South West US, so walls could dampen temperature swings of the interior environment.
Eventually as property values increased, buildings were constructed taller, and the limits of
brick as structural material were reached. The base of brick walls had to be very wide to support
multiple stories. A 16 story building in Chicago was constructed with six foot wide walls at the
base in order to adequately support the structure, which used valuable property for the structure.
8
As buildings got taller, they were less protected by their surroundings, and they were subjected
to harsher environmental conditions and greater wind forces requiring more attention to
enclosure control details, specifically, the rain control functions of the enclosure.
As quality of life improved people demanded better performance, warmer and drier buildings.
There had been many reported cases of damp walls resulting from rain penetration as well as
condensation of moisture in the air on the interior enclosure surfaces of masonry construction.
Thomas Jefferson mentioned these problems as early as 1792 in his writings (Ritchie 1960).
Because of these moisture problems, Johansson (1946) suggested that masonry walls be covered
with “an outer, water repelling screen” since plaster and masonry absorbed water. Incorporating
multiple layers of protection was a new concept for building enclosures. Spurred on by the 1973
oil crisis, people began searching for ways to decrease the amount of energy used in buildings.
One major change was that insulation was added to enclosure walls to minimize heat loss. While
this kept the interior warmer, it also kept the exterior of the enclosure cooler so the exterior did
not receive as much heat to dry the cladding. In cases of outward air leakage, more moisture
could now condense on the cooler enclosure, and in extreme temperatures, freeze thaw damage
became a problem.
These performance issues were coupled with changes in methods of
construction and materials used that may have increased moisture related problems (Ritchie
1960).
Adding an exterior screen to masonry construction was used as a retrofit to help with rain
control in the building enclosure. Using this approach, cavities could also be installed in new
construction to stop moisture from reaching the interior of the enclosure. Initially, the air gap
acted as a capillary break that prevented water from wicking from the exterior to the interior.
Eventually, the cavity wall began to use drainage as a moisture management technique in new
construction. The wall was designed so water that passed the first layer of brick could not reach
the second layer, and would be drained out the bottom through unfinished mortar joints. Careful
construction was required to ensure that water did not bridge the gap between the two layers. As
an added benefit, the air space added insulative value relative to a solid masonry wall, and in
some cases water repellant insulations were installed in the drainage cavity.
9
Expanding on the drained masonry cavity wall, Garden (1963) introduced the “open rainscreen” which used pressure equalization to aid rain control. Pressure equalization is a technique
proposed to deal with water leakage by eliminating the air pressure difference across a cladding.
By adding vent holes in the cladding and allowing air to flow behind the cladding, the air
pressure difference (ie. driving force for liquid water) across the cladding could be removed.
Garden recognized the need for dividers in the air chamber to minimize vertical and horizontal
air movement due to large variations in pressure differences across the face of the wall. He also
suggested that the dividers be put not more than 1.2 m apart around the edges of the building
where the pressure gradients will be greatest, and no more than 6 m apart in the centre of the wall
face.
The key to pressure equalization is a continuous airbarrier on the interior surface of any
pressure equalized component.
After buildings were air tightened, Hutcheon (1964), also of
Canada’s Division of Building Research, improved on the open rain-screen concept by adding a
continuous insulation layer to the enclosure and introducing the idea of a fully insulated masonry
wall. Hutcheon (1964) showed that by installing the insulation near the exterior surface rather
than the interior, the enclosure temperature could be controlled. Controlling the temperature
would help minimize some of the moisture problems previously experienced, as well as reduce
expansion from both thermal and moisture changes. This is still considered an ideal wall system
and has become very popular in cold climates. It has been renamed PERSIST by members of
Alberta Infrastructure (Makepeace 1999) an acronym for Pressure Equalized Rain Screen
Insulated Structure Technique but is simply another name for the method first suggested by
Hutcheon in 1964.
Recent studies have shown that ventilation airflow can remove significant amounts of moisture
from the building enclosure. Schumacher et al. (2003) showed a correlation between the amount
of airflow and the drying rate of the enclosure. Water does not always accumulate in the
drainage gap quickly enough to drain, so the water is stored in the enclosure. Since most
claddings have relatively low vapour permeance, ventilation of the space behind the cladding can
be an important means of both drying and avoiding inward vapour drive wetting (Straube and
Burnett 1998)
10
3.0 Moisture Physics
To better understand the interactions between moisture and wall systems, it is important to
understand the properties of airborne moisture and the physics of moisture storage, wetting, and
drying.
3.1
Psychrometrics: Moisture in Air
Psychrometrics, defined as the study of the heat and water vapor properties of air, is an
important tool for understanding and diagnosing moisture problems. Before 1904 there had been
numerous psychrometric tables used mostly by meteorologists, but Willis Carrier required a
simplified chart method for air conditioning design since he had completed the world’s first
scientifically based air-conditioning system (Gatley 2004).
The properties of air most relevant to building issues are its water vapour content, relative
humidity, and dew point so a simplified psychrometric chart can be used for building related
moisture problems (Figure 3-1). On the x-axis is temperature in degrees Celsius and on the yaxis is the water vapour content of the air measured in pascals.
With information about the moisture content and temperature, one can determine the relative
humidity (RH) which is the ratio of moisture in the air to the maximum amount of moisture that
can be stored in the air at any temperature. The RH is highly dependent on temperature since
warmer air will hold more moisture. The RH lines are curved on the graph, and the darkest line,
labeled 100% is called the dew point line.
The dew point occurs when the air becomes
completely saturated and any excess water vapour added must condense to liquid form. The dew
point is very important in a wall system, since in most cases damage is minimal if water remains
in vapour form but becomes more problematic if it condenses. To better understand the
usefulness of the psychrometric chart, some examples are provided to explain how the chart can
be used.
The amount of moisture in the air can be reported as absolute humidity, vapour pressure,
relative humidity, or humidity ratio since all measures report the amount of vapour in the air.
11
Absolute humidity is synonymous with humidity ratio and is expressed as a ratio using the mass
of water vapour over the mass of dry air (Straube and Burnett 2005)
The vapor pressure is the partial pressure of water vapour in a gas mixture. The partial
pressures of each component in a gas mixture will sum to the total pressure of a gas mixture
according to Dalton’s Law. The partial pressure of water vapour will not change in response to
changes in temperature.
Figure 3-1 : Simplified Pyschrometric Chart
Determining the vapour pressures and saturation vapour pressures throughout the enclosure is
important for all moisture related building enclosure problems. The saturation vapour pressure
PWS, can be found for any temperature T, in ºK, from the following equation.
PWS = 1000 ⋅ e
( 52.58−
6790.5
−5.028 ln T )
T
12
[Pa] ,T>0
(3.1)
Multiplying the saturation vapour pressure by the ratio of moisture in the air to the maximum
moisture the air is capable of holding (ie. RH) determines the actual vapour pressure of any air
sample. The vapour pressures will indicate the vapour pressure gradient (the size and direction
of the force driving vapour diffusion). The amount of moisture that moves is determined both by
the size of vapour pressure difference and by the permeance of the materials, or the resistance to
water vapour. Some materials are designed to be vapour open such as spun bonded polyolefin,
and other materials are used to stop vapour movement like polyethylene sheets. In many places
it is required by the building code to install a vapour barrier in the wall system. There has been
much debate whether or not this is needed in certain climates, and in some places the vapour
barrier is being removed from the building code requirements. Hutcheon (1963) realized that
vapour barriers on the interior in cold climates may lead to durability issues especially when a
wall was subjected to inward vapour drives. Vapour barrier use still continues to be a point of
contention among building scientists.
3.1.1
Psychrometric Examples
To help illustrate the usefulness of the psychrometric chart two basic examples of moisture
problems will be examined. For the first example, there is a small hole in the enclosure (as a
result of damage or poor construction) and indoor air is passing through the enclosure to the
exterior during cold weather conditions (-10ºC). First, locate the interior air conditions of 20ºC
and 30% RH on the chart in Figure 3-2. This point is labeled with A. As the air moves through
the enclosure, the temperature will decrease towards the exterior temperature. On the graph this
is represented by a horizontal line, indicating that the vapor pressure or absolute humidity stays
constant. As the air cools, the relative humidity of the cooler air increases since the air is unable
to store as much moisture. Eventually, the air will approach 100% relative humidity. The
temperature at which air reaches 100% RH is the dew point and in this example the dew point
occurs at 2ºC.
Since the air is cooled further to -5ºC, the air will follow the 100% relative
humidity curve until it reaches -5ºC (Point B), condensing water on the back of the sheathing or
any other cold surface. If the volume of air flowing through the wall system can be determined,
it is possible to calculate the amount of condensation. If the condensation surface is below
13
freezing the condensate will usually form as frost, and continue to accumulate until the weather
changes, the sheathing is warmed, and the ice melts. This type of example is quite common in
attics, where large amounts of ice or water form on the underside of the cold roof sheathing.
The psychrometric chart can also explain why it feels so dry inside many buildings in the
winter months. Most HVAC systems recycle internal air to some degree, but the air they take
from the exterior as fresh air could be below freezing. By looking at the psychrometric chart, we
know that air at -10ºC has a vapour pressure of 250 Pa if it is 100% saturated (Point C). As the
air is warmed for distribution, often no moisture is added, keeping the vapour pressure constant.
As the air is warmed to 20ºC, the relative humidity decreases below 20% (point D). This is why
it often feels very dry indoors during the winter months.
Figure 3-2 : Practical Examples using the Psychrometric Chart
It is often desirable to maintain a low RH in the winter especially in older houses or houses
with poor windows. The psychrometric chart illustrates how easy it is to condense vapour on the
14
cold surfaces such as windows in the winter. Windows are often the coldest interior surface in
the winter because of their inherently poor insulative quality. Similar to the air leakage example
if the interior conditions are 20ºC and 30% RH the dew point is approximately 2ºC, this is the
temperature at which a window must be kept above to avoid condensation. This is often
accomplished by installing heat sources under windows, but may also be accomplished by
installing higher quality (ie. better insulated) windows. Increasing the interior RH either by
cooking and bathing, or by mechanical means such as a humidifier increases the dew point of the
interior air and hence the window temperature must be kept warmer to avoid condensation.
3.2
Moisture in Materials
Water can be stored in all three states; liquid, vapour, and solid. Water stored as solid ice can
be important when dealing with freeze/thaw damage, but only liquid and vapour storage will be
examined here. Liquid water is either stored on the surfaces of a material or absorbed into the
material and water vapour is stored as adsorbed moisture. The moisture storage of any material
can be determined from the sorption isotherm which relates the moisture content of a material to
the relative humidity of surrounding air (Figure 3-3).
Solid materials in the presence of water vapour will tend to hold vapour molecules in a
phenomenon called adsorption. The amount of vapour a material can hold is dependant on the
temperature, amount of moisture in the air (ie. partial pressure), surface area, and the physical
properties of the material.
As the partial pressure increases from zero, water molecules become adsorbed in a
monomolecular layer and eventually in multimolecular layers inside the pores of a material. This
continues until the layers become thick enough to form liquid water or frost (Kumaran et al.
1994). The range of moisture from completely dry to the first point of liquid water is called the
hygroscopic range of a material.
15
Figure 3-3 : Components of a sorption isotherm for a hygroscopic material (Straube and Burnett
2005)
Liquid water storage occurs when the material comes in contact with liquid water or when the
relative humidity is high enough to start condensation in the pores of the material. When this
happens the amount of water stored will depend on the number and size of the pores. Larger
pores will fill up first and the smallest pores will fill up second based on capillary flow explained
in Section 3.4. Capillary action generally starts at very high RHs after all the pore spaces have
been covered by layers of water vapour molecules. Above capillary saturation, additional water
added to a material will drain out if possible. Supersaturation can often occur in enclosure
assemblies if drainage is not allowed.
At the surface of wet materials, the RH will be 100%. If the temperature of the air around
such a material is kept the same as the material, water vapor will move from the wet material to
the drier air by diffusion.
16
Figure 3-4 shows some typical sorption isotherm curves for three different materials with
different physical characteristics. The shape of the curve is determined by the hygroscopicity of
a material, that is, the affinity a material has to water and its pore structure (Sereda and Feldman
1970).
Figure 3-4 : Sorption isotherms of various materials (Hutcheon and Handegord 1995)
Wood is shown to have a high adsorption (typical of organic substances) because of its
relatively large number of small pores. Brick is inorganic and when well fired, has relatively few
small pores so only adsorbs moderate amounts of water at lower and intermediate relative
humidities (Handegord and Hutcheon 1995).
Concrete is much more complex because of
variables in a concrete mix. The aggregate, cement paste, water content, and admixtures will all
affect the sorption isotherm, but the sorption isotherm will generally lie between brick and wood,
because of the range of pore sizes in concrete.
Sorption isotherms can be developed for any material by subjecting the material to different
relative humidities until equilibrium is reached, and then weighing the samples to determine the
amount of moisture adsorbed to the test material.
17
3.3
Moisture in Assemblies
Sections 3.1 and 3.2 described the moisture storage in air and materials respectively, but most
important to the building enclosure is how the water is stored within the assembly itself. Figure
3-5 summarizes the possible storage mechanisms in a wall system.
1. captured water in poorly or undrained areas
2. stored as droplets (or ice) on the surface of materials
3. adsorbed to hygroscopic building materials
4. absorbed into a material by capillarity
5. stored as vapour
5
3,4
2
1
3,4
Figure 3-5 : Moisture Storage in Wall Assemblies (Straube and Burnett 2005)
18
3.4
Moisture Movement
Moisture will only move if acted on by a force. In wall systems the forces usually responsible
for moving water are capillarity, gravity, air movement, and diffusion.
3.4.1
Capillarity
Capillary forces act as a result of surface tension, and can suspend and move water against the
force of gravity. One example of this can be seen in a small tube such as a drinking straw
(Figure 3-6). The level of water inside the straw is higher than the surrounding water because of
the surface tension between the fluid and the inside walls of the straw.
Figure 3-6 : Capillary suction of water in a tube (Straube and Burnett 2005)
The height of the rise in the fluid is determined by fluid and surface characteristics as well as
the diameter of the pore (ie. straw) and can be calculated from:
h=
2σ cos(θ )
gρr
h – height of capillary suction (m)
σ – surface tension (σ =0.072 N/m or J/m2 for distilled water at 20ºC)
r – pore radius
ρ – fluid density (N/m3)
θ – contact angle between fluid and surface (deg) (Figure 3-7)
g – gravitational acceleration (m2/s)
19
(3.2)
Using the following equation for pressure (P) due to gravity,
P = ρgh
(3.3)
ρ = fluid density
g = gravitational acceleration
h = height of fluid
a column of water 10mm, 1m and 10m high results in pressures of 100, 10,000 and 100,000 Pa
respectively. Simplification of the capillary rise equation (3.2) becomes
Pcap =
2σ cos(θ )
r
(3.4)
Using equation (3.4) and solving the capillary pressures for pore sizes typical in concrete and
wood results in suction pressures between 100 kPa and 10 MPa. These calculated pressures
show that in small pores, the capillary suction pressures greatly exceed gravity pressures of
water.
Capillary forces can be important in several places in a building. One area of importance is in
concrete and masonry wall construction as discussed earlier in Secion 2.2.
Concrete and
masonry walls need a drainage cavity inside the wall or a capillary inactive moisture barrier on
the exterior to avoid absorption and capillary movement of water to the interior surface. Another
important location for capillarity are connections between concrete and wood framing usually
found where a wood frame structure joins the foundation. These connections must have a
capillary break to limit the movement of moisture across the interface so moisture can not be
wicked up from the foundation.
The contact angle of any material is important to both moisture movement and storage. Figure
3-7 shows the characteristic contact angles for a droplet of water on a wettable hydrophilic
material on the left, and a non-wettable hydrophobic material on the right. Equation (3.2 shows
that if the contact angle is 90º (ie. The material is between wettable and non-wettable) then the
capillary rise is zero. If the contact angle is greater than 90º than the capillary rise is negative,
20
and the level of water in the straw will form below the level of the surrounding water. This is
examined further in Chapter 5 for the drainage gap analysis.
θ < 90o
θ > 90o
θ
θ
normal material:
“wettable”
hydrophobically treated:
“non-wettable”
Figure 3-7 : Contact Angles
3.4.2
Gravity
Gravity is often cited as the most important force driving rain penetration. Gravity can also
provide assistance in keeping moisture out of the building and is the basis of the drained
approach to rain control. The force of gravity by the earth can be calculated on any object using:
F = mg
3.4.3
(3.5)
Air Movement
Air movement is one of the leading causes of premature enclosure failure (rain penetration
being the other). Air movement through the enclosure is caused by air pressure differences
across the enclosure. Air pressure differences can be induced by mechanical conditioning
equipment, stack effect or wind pressures.
Stack effect occurs in buildings due to differences in air density with temperature. The amount
of pressure induced by stack effect corresponds to temperature differences, and the height of the
21
building. The only way to stop air movement across the enclosure is with an airtight barrier.
This can be quite difficult in practice because of the penetrations through the enclosure for
windows, doors, and services.
3.4.4
Diffusion
Diffusion is the movement of mass from an area of high concentration to areas of low
concentration. An example of diffusion can be seen if coloured water is dropped into pure water
in a container. Eventually, without any assistance, the water in the container will be uniform in
color. Water vapour is similar, and will try to move from areas of high concentration to areas of
low concentration proportional to the vapour pressure gradient and material diffusivity:
M& = Dv ⋅ ∆Pv
(3.6)
M& = mass flow rate
Dv = vapour diffusivity
∆Pv = vapour pressure gradient
Building enclosure problems due to vapour diffusion tend to be less significant than air
leakage problems but can still cause durability issues and therefore should be considered in the
design.
3.5
Wetting
The most serious moisture damage in wall systems and buildings is caused by bulk water,
whether it is from rain, condensation, or faulty plumbing.
Moisture problems can also result from condensation of large amounts of moisture in the air.
The water vapour in interior air can be transported to cold areas of the enclosure by air
movement. The likelihood and significance of wetting strongly depends on the interior humidity
and exterior temperature. Museums and art galleries are often required to keep the interior
relative humidity quite high to protect exhibits, often leading to moisture problems, especially in
cold climates.
22
The sun’s energy can also force moisture into the enclosure by imposing a high vapour
pressure difference across the enclosure. Inward vapour drives may lead to serious durability
problems in locations of high humidity such as Florida, where it is common to find mold on the
back of vinyl wallpaper. If the wall paper was removed, the interior surface may allow enough
vapour to escape from the enclosure into the interior, avoiding mold growth.
3.6
Drying
Once building enclosure materials get wet, they must dry or moisture damage will occur. The
amount of damage and the length of time before damage occurs vary for different materials. It is
possible for walls to dry to the interior or to the exterior depending on the composition of the
wall and the driving forces. There are four basic ways for wall systems to dry (Figure 3-8).
1. Evaporation of water that has been moved by capillarity to exposed surfaces
2. Diffusion/Air leakage inward or outward
3. Drainage
4. Ventilation
23
4
1
1
2
3
2
1
3
Figure 3-8 : Drying Mechanisms for Wall Systems
The driving forces most responsible for drying of the building enclosure are solar energy, and
air pressure (from wind and stack effect).
3.6.1
Wind
As unsaturated air moves over wet materials it can accept moisture into the air stream. The
amount of moisture transfered depends on air flow velocity, surface roughness and properties of
the air. Ideally, the dry air would be in contact with the wet materials for enough time to become
completely saturated. Ventilation airflow occurs through holes produced in the cladding that
allow air to pass behind the cladding into the ventilation gap.
Some cladding systems are inherently self ventilated such as clapboard siding as shown in
Figure 3-9.
24
Figure 3-9 : Ventilation of Directly Applied Siding (Van Straaten 2005)
25
4.0 Rain Control Strategies
All functions of the enclosure (Section 2.1) are important, but experience has shown that most
moisture problems are due to a failure to properly control heat, air or moisture. The finish
function is aesthetic, and does not contribute to overall enclosure durability and the support
function has been well studied by structural engineers, and hence buildings can be constructed
with extremely low risk of structural failure.
Moisture damage in the building enclosure can only occur if four requirements are met; a
source of moisture, a path for moisture, a driving force, and moisture susceptible material. By
removing one or more of these requirements, the durability of the building enclosure can be
ensured.
The so-called “4Ds” strategy for rain management is a strategy that uses Deflection, Drainage,
Drying and Durability (Morris and Hazleden 1999, Kerr 2004). Durability is a result of the first
three strategies rather than a strategy itself, but it can be argued strategies such as using pressure
treated lumber instead of normal lumber is a durability strategy.
Using the strategies of
deflection, drainage and drying will lead to increased durability so some authors, such as Straube
and Burnett (2005) do not include it. Deflection, Drainage, and Drying strategies are discussed
below.
4.1.1
Deflection
The first level of moisture management is deflection. Keeping walls dry is an important
strategy to preventing moisture damage in enclosures. Ritchie (1960) knew that overhangs were
a valuable feature and that they would help a great deal in protecting low rise buildings.
Morrison Hershfield conducted a study in 1997 and found that walls protected by overhangs on
low-rise buildings were less likely to have moisture problems (Figure 4-1) (Morrison-Hershfield
1997). As buildings get taller, overhangs offer less protection against rain, windspeeds increase,
and walls get much wetter.
26
Figure 4-1 : Correlation of Overhang Size on Low Rise Buildings and Wall Problems Due to Water
in Vancouver, B.C. (Morrison-Hershfield 1997)
Carefully planning the site layout will help deflect water from the building with various
strategies such as constructing a low rise building, using landscaping, trees, and the surrounding
buildings. Deflection can also be ensured with design details such as drip edges or ridges in the
wall cladding that direct water away from construction elements such as windows, and to stop
water from running along the bottom of edges of materials back towards the enclosure.
Understanding the wind and rain patterns in an area can help with site and building planning to
minimize driving rain exposure and maximize deflection strategies. Driving rain roses can be
found for many locations such as Toronto and Vancouver (Figure 4-2). These rain roses are
specifically for driving rain, and were developed to illustrate driving rain patterns for different
locations (Straube and Schumacher 2005). Driving rain is calculated for all of the 16 directions
on the rain rose from wind direction and horizontal rain measurements. The value for each
direction is plotted on the graph. In Toronto, there is approximately 130 mm/yr of driving rain
from the east, and approximately 35 mm/yr from the west. In contrast, in Vancouver, there is
approximately 450 mm/yr from the east, and very close to 0 mm/yr from the west. Graphically
representing rain data for specific geographic locations with a rain rose will helps illustrate risks
27
associated with driving rain as well as help determine the level of rain control needed for
successful enclosure durability. Driving rain is examined further in Chapter 5.
Figure 4-2 : Driving Rain Roses for Toronto and Vancouver (Straube and Schumacher 2005)
4.1.2
Drainage, Exclusion, Storage
Attempting to entirely deflect rainwater from contacting walls is difficult and impractical.
Hence, it must be assumed a wall system will be exposed to rain water. There are three main
control strategies for handling externally applied liquid moisture: Exclusion (perfect barriers),
Storage (mass walls), and Drainage (rainscreen). These three strategies as well as subcategories
are illustrated in Figure 4-3.
28
Joints
Elements
Imperfect Barrier
Mass or
Storage Types
Less mass
and lower
permeability
Drained or
Screened Types
Perfect Barrier
Types
More mass
and more
permeability
Cavity
Ventilated
Perfect Barrier
No Cavity
Vented
Face
Sealed
Concealed
Barrier
Unvented
Pressure moderated
Figure 4-3 : Rain Control Stategies in Wall Systems (Straube and Burnett 2005)
One enclosure strategy developed to control rain penetration is the perfect barrier system, is
based on the principle of exclusion. This system relies on one layer of impermeability, be it
glass, metal, or other material. Panels made of glass or metal are in fact impermeable to water,
unless cracked, but the joints between the panels almost always fail and allow water penetration.
It very difficult to construct a wall as a perfect barrier system, so most walls are designed as an
imperfect barrier system, using either the storage or drainage strategies.
29
A mass wall controls rainwater penetration by storing and subsequently drying any water that
penetrates the exterior. Mass wall systems are not used as commonly as they have been in the
past. As discussed earlier in section 2.2, they do not perform as well as other systems with
regards to moisture management. They can still be found in both commercial and industrial
uses, where a small amount of moisture passing through the enclosure is not a concern.
The third category of water management is the drained or screened wall system. As previously
discussed, one of the first references to a drained wall system was Johansson (1946) who
suggested that masonry walls be covered with “an outer, water repelling screen” since plaster
and masonry absorbed water. This rain control concept was furthered by Ritchie in 1961 who
introduced a cavity wall, so water that passed the cladding would not enter the interior enclosure
layers. Pressure equalization can be added to a drained wall to reduce the amount of water that
needs to be drained. These ideas are not new, yet building enclosures still often fail to control
rain because of an improperly designed or constructed drainage system.
There are four necessary requirements of any successfully drained wall system (Lstiburek
2003). These requirements are a drainage plane, drainage space, flashings, and weep holes
(Figure 4-4). The drainage plane must be continuous over the entire area of the wall and must
connect to openings in the enclosure such as windows, doors, and services. It is important to
overlap drainage plane materials correctly, or water may be directed into the wall instead of the
drainage cavity. Overlapping materials can be compared to a rainsuit, whereby overlapping
incorrectly, all the water will run into the boots or in this case, the house. The wall system must
incorporate a drainage space that allows for water to drain and ideally, the space should be wide
enough that water does not pass from one surface to the other. At the base of the drainage space,
and all penetrations and intersections, flashing is required to direct water out of the drainage
space. Weep holes are required at the bottom of any drainage cavity to direct any drained water
to the exterior.
30
Head flashing
Sub-sill flashing
Drainage space
over drainage plane
Weep (Drainage)
Holes
Sloped Grade
Figure 4-4 : Requirements for Drained Wall System (Straube and Burnett 2005)
In areas such as Vancouver, where there is a history of building enclosure failure, officials
have legislated a drainage gap in their building code. The by-law states, “While there is
agreement on the need for a cavity, current research is not conclusive on the optimal width of a
cavity to maximize drying potential,” (Vancouver Building Code 1999). The by-law states that a
19mm (3/4”) cavity is the minimum width recommended in construction, but also reports that
research has shown that a 10 mm gap is sufficient to prevent water from moving across the gap.
For this reason the by-law allows a 12 mm (1/2”) gap if the building envelope professional can
assure that a 12 mm gap will be maintained.
The drainage gap is usually included by design, for example, by using strapping, the space
between two layers of building paper, or by applying the EIFS adhesive in vertical stripes
allowing water to drain in the spaces. The drainage gap can also be included by accident such as
when building paper swells and wrinkles after wetting, or by vertical wrinkles caused by uneven
installation of the building paper (Straube et al. 2000).
31
4.1.3
Drying
The third part of moisture management is drying. When rain water hits the enclosure surface,
or penetrates, some moisture will be stored in the wall system (see Section 3.3). Water can be
stored as absorbed moisture, adsorbed moisture, or on the surface of wall materials. The moisture
stored in the wall must be dried in a timely manner to avoid moisture related durability issues.
The amount of drying required will depend on the physical characteristics of the enclosure, the
environmental conditions on both sides of the enclosure, and the frequency and intensity of rain
events.
Drying of water stored on the back of the cladding, in the drainage gap or in the drainage plane
can be accelerated by ventilation drying. In this approach, vent holes are connected to an air gap
(the drainage gap) and drier outdoor air moves through the gap under the natural forces of wind
pressures and thermal buoyancy.
32
5.0 Research Program
Using a rainscreen wall construction strategy and promoting drainage and ventilation drying is
generally accepted as the best method of enclosure design in geographic areas subject to regular
precipitataion (Lstiburek 2003, Ritchie 1961) and is required in some areas (Vancouver Building
Code 1999). However, despite its popularity, there remain several important questions about
drained systems. It is unclear what drainage loads can be expected in a wall system, and how
large of a space is required for adequate drainage. The drainage gap is also useful for ventilation
drying of stored water, but the amount of space required for adequate ventilation drying has also
not been determined.
Standards (eg. ASHRAE 160P) are being developed to design wall systems to accommodate a
percentage of wind driven rain getting past the cladding. This thesis is relevant because it
examines the amounts of water that might be expected to pass the cladding as well as the wall’s
response to leakage.
5.1
Objectives
One objective of the research program is the determination of the quantity of drainage possible
for a range of gap sizes and typical rain loads. The amount of water stored, and hence the
amount of drying is required for different wall systems, will also be studied. Finally the ability
of different gap sizes to allow ventilation drying will be investigated.
5.2
Approach
A theoretical analysis of drainage was undertaken to determine the maximum flowrates
possible in different gap widths using a modified Darcy-Weisbach equation for pipe flow. This
analysis will help determine the width of drainage gap necessary for adequate drainage.
Canadian driving rain data was analyzed for many locations to determine the types of driving
rain loads that are expected for both average and extreme rain events. Analyzing the driving rain
33
will help determine moisture loads that building enclosures are subjected to in different locations
and from different directions.
An experimental test method was designed to determine how much water is stored in different
wall systems and the ability of these walls to dry. Tests were conducted on many different wall
systems both with a continuous drainage gap and a discontinuous drainage gap developing a
suitable test method and approach.
34
6.0 Drainage Gap Analysis
This chapter presents the results of a theoretical analysis conducted to determine drainage flow
rates as a function of gap thicknesses based on fluid flow properties. The goal of this analysis is
to determine minimum gap widths required for drainage, and in later sections compare these gap
widths to predicted leakage rates and test protocols for drainage.
6.1
Assumptions
For the theoretical analysis, it was assumed that there were no air pockets in the fluid flow.
From physical observations of plexiglas clad walls, we know that this is not the case, and that the
flow in the gap is a mixture of air and water pockets. The assumption of fully saturated flow was
used to simplify the calculations considerably.
Another important assumption is that the cavity flow is laminar. This assumption will be
confirmed during the calculations. Finally, it was assumed that the materials forming the gap are
non-absorptive and that there is negligible head loss at the inlet and outlet of the cavity.
6.2
Theoretical Maximum Flowrate
To determine the flow of water through a gap, the gap was assumed to be a fully saturated
rectangular conduit, with flow driven by gravity head and resisted by friction. The DarcyWeisbach equation is widely used to calculate the head loss in a conduit due to friction and the
flow characteristics.
L V2
h f = f ( )( )
D 2g
hf – energy loss per unit weight of fluid (J/N = m head)
f – friction factor (dimensionless)
L – length of conduit (m)
D – diameter of conduit (m)
V – fluid velocity (m/s)
g – gravitational acceleration (m2/s)
35
(6.1)
This equation can be used to correlate energy loss (head) and flow velocity and in this case, the
maximum flow for any gap size. Given a fixed height of conduit and gap size, the maximum
sustainable flow can be calculated assuming the full height is filled with water. If additional
pressure is added (from some external source such as wind or air pressure), the flow rate will
increase.
Since the Darcy-Weisbach equation is generally used for pipe flow, D represents the diameter
of the pipe. In the case of a drainage gap, the hydraulic diameter can be substituted for the pipe
diameter. The hydraulic diameter can be calculated by using:
Dh =
4A
P
(6.2)
Dh – hydraulic diameter
A – cross-sectional area
P – wetted perimeter
The equation for hydraulic diameter can be applied to gaps by defining the length and width of
the gap as l and w respectively and simplifying equation 6.2 as:
D=
4(l × w)
2(l + w)
When the gap becomes quite small the gap width, w, becomes insignificant in the denominator
and the hydraulic diameter can be simplified.
D=
2(l × w)
l
The length cancels out in the top and bottom resulting in
D = 2w
(6.3)
The relationship between the full and simplified forms of the hydraulic diameter is presented
in Figure 6-1 for a cavity in a one meter wide wall. The simplification is quite accurate for small
gaps, i.e., less than 15 mm. Even at a gap width of 25 mm the error is less than 3%.
36
70
Hydraulic Diameter (mm)
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
Gap Width (mm)
Simplified Hydraulic Diameter
Actual Hydraulic Diameter
Figure 6-1 : Comparison of Actual Hydraulic Diameter (equation 4.2) to Simplified Hydraulic
Diameter (equation 4.3)
The friction factor in the Darcy Weisbach equation describes the roughness of the conduit
walls. The friction factor can be calculated, assuming the flow is laminar, for a non-circular pipe
from the following equation.
f =
k
Re
(6.4)
f – friction factor
k – geometry factor (96.0 for parallel plates)
Re – Reynolds number
The Reynolds number can be found from
Re =
VD
v
V – fluid velocity [m/s]
v – dynamic viscosity [m2/s]
D – hydraulic diameter [m]
37
(6.5)
Calculating the Reynolds number will show whether the flow in the gap is laminar as assumed,
or turbulent. Generally, a Reynolds number less than 2000 indicates laminar pipe flow. Fully
turbulent pipe flow is expected for a Reynolds number greater than 10,000, while in between the
values of 2000 and 10,000, the flow is considered transitional with some laminar and turbulent
characteristics.
Once the calculations are done, the assumption must be checked for the
calculations to be valid since a different friction factor is needed for turbulent flow.
A range of gap sizes from 0.1 to 20 mm was used in the analysis. This range was selected to
reflect the range of equivalent gap sizes found in real wall systems.
The Darcy-Weisbach equation can be modified to represent two different cases. Case I occurs
when the conduit is not full (Figure 6-2) and the head formed by gravity pressure, ‘hf’ is
equivalent to or less than ‘L’. This simplifies the Darcy Weisbach equation (4.1) to:
hf
L
= 1.0 =
f V2
D 2g
Substitutions can be made for f and Re from equations 5.4 and 5.5 so that,
1=
96 V 2
96v V 2
and 1 =
Re D 2 g
VD 2 2 g
This can be simplified, and solved for V.
V=
2 gD 2
96v
(6.6)
This equation shows that the velocity of saturated flow in a vertical cavity is only a function of
the changing gap width D, which means that the velocity will be constant for any level of water
in the conduit. This velocity is governed only by the width of the gap and water viscosity, not by
the roughness of the surfaces and head. See Table 6-1 for a range of values.
38
Q
Case I
Case II
Q
R.O.W.
Cladding
Cladding
hf
L
R.O.W.
hf=L
Q
Q
Figure 6-2 : Case I and II for Drainage Analysis (Note: R.O.W. = Rest Of Wall)
Table 6-1 : Case I flow velocity and rate as a function of gap width
Gap (mm)
V (m/s)
0.1
0.002
0.204
0.5
0.051
25.5
0.8
0.115
86.2
1.0
0.204
204
1.5
0.460
690
2.0
0.818
1635
39
Q(ml/s-m width)
Figure 6-3 shows the flow rates corresponding to different gap sizes. The flow rates will stay
constant for a given gap size as long as the height of water does not exceed the height of the
drainage cavity. The curved line in Figure 6-3 represents the no flow line where the amount of
water in the gap is not enough to overcome the capillary forces. This is explained further in the
minimum flow section.
2000
0.5 mm
0.75 mm
1.0 mm
1.5 mm
2.0 mm
1800
1600
Flow (mL/s-m)
1400
1200
No Flow Line
(Capillary Retention)
1000
800
600
400
200
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Head (m)
Figure 6-3 : Case I Drainage Analysis
The second case for the flow equation occurs when the head becomes greater than the height
of the drainage apparatus (Figure 6-2). Because of the characteristics of the equation, the extra
head is not subject to the same friction. An example of this could be when water is funneled
down a roof into a wall, or from a window into a cracked joint between a jamb and a sill. Extra
pressure head may also be created by air pressure from strong winds. The equation for the
second case is:
40
V=
h f 2 gD 2
(6.7)
96vL
The difference between case 1 and case 2 is that hf/L is not equal to one in case 2. In case 2
there are three variables that determine the velocity or flow of water in the gap; the length of the
gap, the gap thickness, and the head pressure. The flow rates were calculated and presented in
Figure 6-4 for Case II using different gap sizes and ratios of hf/L. The minimum flow line that
was included in the case I graph could not be included with these axis, but it is understood that
these flows would stop before they reached zero.
The events of a negative pressure have also been included. Negative pressures could be
induced from high winds.
6000
0.1 mm
0.75 mm
1 mm
1.5 mm
2 mm
5000
4000
Flowrate (mL/s-m)
3000
2000
1000
0
-1000
-2000
-3000
-1.5
-1
-0.5
0
0.5
1
1.5
hf/L
Figure 6-4 : Case II Drainage Analysis
41
2
2.5
3
3.5
Because the extra head is not subject to the same friction, the flow will increase
proportionately to the gap width cubed and linearly with increasing head pressure. This means
that the larger the gap width, the faster the rate of increase for the velocity.
The limitation of this analysis method is that water must be in contact with both sides of the
drainage gap, requiring a large amount of water in most cases. Only in gaps smaller than
approximately 5mm does the water naturally touch both sides, bridging the gap, as it travels
down the wall.
Reynolds numbers need to be calculated from the velocities to confirm the assumption for
laminar flow. Nearly all of the values are less than the critical value of 2000. In the 2 mm gap,
once the flow goes beyond 1 m/s the flow enters the transitional range. A velocity of 1 m/s in a
2mm gap corresponds to a flow rate of 580 mL/s which is unrealistically high. Transitional
values for Reynolds number range from 2000 to 10,000. The largest Reynolds numbers
calculated in the analysis of the 2mm gap were 3400. Because the flows required to reach
transitional values of the Reynolds number are unrealistically high for a building system, they
will be disregarded in this analysis.
6.3
Theoretical Minimum Flowrate
The minimum flow in a gap will be determined by the pressure (head) required to overcome
the capillary action of the drainage gap. The height of capillary rise in any gap was already
shown in Equation (3.2.
The rise due to capillary suction was calculated for a range of gaps from 0.1 to 2.0 mm (Figure
6-5) using different contact angles between the fluid and the gap material. The contact angle of a
material was explained previously (Section 3.4) but the role the contact angle plays in capillary
rise is shown in Figure 6-5. The smaller the gap becomes the larger the influence that capillary
retention plays on the flow in a drainage gap. While capillarity may not stop water from flowing
in practice, it does give an indication of how much water could be trapped in a wall system after
a wetting event. Trying to maintain small gaps in the range of 0.1 mm is impractical in field
applications due to uneven surfaces, but small gaps do occur unintentionally in wall systems.
42
600
Height of Calillary rise (mm)
500
0º
400
45º
30º
60º
135º
300
200
100
0
-100
-200
-300
-400
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Gap Width (mm)
Figure 6-5 : Capillary Rise in a Gap Between Plates For Different Contact Angles
6.4
Conclusions
Based on saturated flow, even small drainage cavities (1mm) can drain significant amounts of
water (204 mL/s-m). Flow rates in drainage cavities that are not full of water (Case I) are only
dependant on the drainage gap width and the fluid viscosity. In cavities where there is extra head
(Case II), the flow rate increases proportionally to the gap width cubed and linearly with
increasing head pressure.
All of the realistic drainage flow rates in the analysis were confirmed to be laminar.
It is possible for the flowrate to be controlled by capillarity at very low flow rates and small
gap sizes, but is more likely that water will be trapped in wall cavities when the gap becomes
small.
43
7.0 Analysis of Drainage Loads
There are four sources of moisture in a building, as explained in chapter 1, and the most
problematic moisture source for building enclosure durability issues is driving rain. Determining
the rainfall, windspeed and direction during a rain event is important for moisture loading design
of the enclosure. If rain only fell straight down, there would be much less risk associated with
moisture in wall systems, but even a small amount of wind occurring simultaneously with rain
will change the angle at which rain falls. The goal of this analysis is to determine the rain loads
on building enclosures in average and extreme rain events. These values will be used to
determine water ingress and to compare to testing standards.
Driving rain is generally quantified by one of three methods; experimental, semiempirical or
numerical. The history of driving rain and wind driven rain measurement is covered thoroughly
by Blocken and Carmeliet (2004b) and will only be briefly summarized in this thesis.
7.1
Development of Driving Rain Analysis
Experimental methods consist of field measurements of driving rain.
Driving rain
measurements started as early as 1816 (Middleton 1969) and have helped understand moisture
loads of buildings. Some of the difficulties with using driving rain measurements to predict
moisture loading are that driving rain data is not available for many locations, and data is not in a
readily available format to analyze.
These problems with experimental data have lead to the development of driving rain equations
which calculate the amount of driving rain from meteorological data such as wind speed, and
rain on a horizontal surface. Hoppestad (1955) developed one of the first wind driven rain
(WDR) equations that most semiempirical equations today are based on. It takes the form:
Rwdr = κ ⋅ U ⋅ Rh
(7.1)
The coefficent κ was used to relate the rain on a horizontal surface (Rh) and the wind velocity
(U) to the collected wind driven rain (Rwdr). The coefficient was called the WDR (Wind Driven
44
Rain) coefficient and was determined by measurements at 4-way free WDR guages in four
different locations; Oslo, Bergen, Trondheim and Tromsö. An average value of 0.180 was found
to correlate WDR to horizontal rain and windspeed.
Lacy (1985) further refined Hoppestad’s equation with an analysis of rain drop size and
terminal velocity, which leads to the following equation:
R wdr = 0.222 ⋅ U ⋅ R h
0.88
(7.2)
The exponent 0.88 in equation (7.2 can be omitted for a close approximation (Blocken and
Crameliet 2004). The coefficient is the inverse of the of the terminal drop velocity and studies by
Straube and Burnett (1997), and Kuenzel (1994) have confirmed that the value for the coefficient
ranges between 0.20 and 0.25 for average conditions. However there can be a large variation in
the coefficient from 0.5 for a drizzle to 0.15 for intense rainstorms (Straube and Burnett 1997).
Equation (7.2 determines the amount of driving rain passing through a vertical surface in an
undisturbed air stream. It does not take into consideration the wind effects caused by buildings
and other obstructions. Equation (7.2 was further developed to account for obstructions as well
as the angle from the rain direction relative to the wall.
Rdr = α ⋅ U ⋅ Rh ⋅ cosθ
(7.3)
The coefficient α is referred to as an adapted driving rain coefficient taking into account local
effects as well as the original WDR coefficient (Blocken and Carmeliet 2004b). This equation
was extended by Straube and Burnett (2004) to separate the adapted driving rain coefficient ( α )
into the driving rain factor (DRF) and the rain deposition factor (RDF) in equation (7.4). The
DRF value is similar to the WDR coefficient in equation (7.2 and is shown to be between 0.2 and
0.25 s/m for an average rain event.
rvb = RDF ⋅ DRF ⋅ cos(θ ) ⋅ V (h) ⋅ rh
rvb = rain deposition on a vertical building surface (l/m2/h)
RDF = rain deposition factor
DRF = driving rain factor (s/m)
θ = angle between the driving rain and the normal to the surface
45
(7.4)
V(h) = wind velocity at height of interest (m/s)
rh = rainfall on a horizontal surface (mm/h)
The RDF value is a ratio of the amount of rain in the air stream to the amount of rain that is
deposited on a building at a specific height above grade. This value depends on building size
and geometry such as the overhang and the ratio of building width versus height. Figure 7-1
shows some typical values found from driving rain monitoring and modeling on typical low rise
construction such as a residential bungalow. Different shapes and sizes of buildings have
different RDF values. For example, the upper corners of a tall building or a building without an
overhang will have an RDF of approximately 1.0 (Figure 7-2). Typically, the RDF is much
lower than one.
Another method to determine wind driven rain is numerical analysis. This is much more
labour intensive and is not used for quick estimations. Numerical methods determine the wind
flow pattern around the building by solving the complex three dimensional Reynolds-averaged
Navier-Stokes equations with computational fluid dynamics (CFD) code as well as calculating
the raindrop trajectories (Sandberg 1974, Choi, 1991, Blocken and Carmeliet 2000). There is a
large amount of preparation work required, long calculations times, and large amounts of
memory required. Numerical methods have been shown to be significantly more accurate and
more reliable than the semi-empirical methods according to Blocken (2004), but it is not a
practical solution in most cases because of the above mentioned drawbacks, and great expense.
Furthermore, it is not usually necessary to know the driving rain pattern with such accuracy since
building enclosure design is conservative in nature.
Figure 7-1 : Estimated RDF values (Straube and Burnett 2005)
46
7.2
Case Study
A hypothetical scenario was developed for this thesis to understand the possible rain loads a
building may encounter and how rain loads correspond to water leakage rates in the enclosure.
First, typical hypothetical design deficiencies are located on the side of a building. Next,
Canadian rain data will be examined to determine what application rates of water and air
pressure will contact the deficiencies. In the last section of the case study, water ingress rates
through the deficiencies will be estimated based on water ingress studies conducted on full scale
wall systems by others. These theoretical leakage rates will be compared to standard testing
amounts as well as to the theoretical drainage analysis already discussed.
7.2.1
Building Design Deficiencies
The building for this case study is two stories tall (6m), with no overhang and is shown in
Figure 7-2. The RDF values for this building shape range from below 0.5 in the centre area to
approximately 1.0 in the upper corners.
Figure 7-2 : Theoretical Building and Deficiency Locations
The hypothetical building was designed with typical deficiencies known to allow water entry
into walls and are summarized below in Table 7-1.
47
Table 7-1 : Deficiency Descriptions
Number
7.2.2
Deficiency
1
Broken or missing end jamb on window
2
Missing sealant on ventilation duct
3
Broken or missing end jamb on window
4
Missing sealant on electrical outlet
Calculating Driving Rain
The first step in determining how much water enters through the deficiencies is to determine
the amount of driving rain at each deficiency using rain data. The driving rain load will be
calculated for an average quantity of driving rain as well as for an extreme rain event.
In a recent CMHC rain study by Straube and Schumacher (2005), climatic data for 42 cities
across Canada was collected. This data included rain, wind speed and direction, and wind speed
and direction during rain events. The data from this study was used to calculate driving rain
loads in an undisturbed air stream based on equation (7.4).
Figure 7-3 shows the total driving rain for eighteen of the monitored cities but does not
quantify rain intensity during individual rain events. The three cities with the highest average
yearly driving rain are Sydney NS, St. Johns, NF and Saint John, NB, all of which are on the east
coast. The direction of driving rain differs between cities, and for this analysis, the calculated
driving rain is on the worse possible orientation with the highest exposure.
48
Figure 7-3 : Total Average Annual Driving Rain in the Worst Wall (Straube and Schumacher 2005)
To determine the driving rain from an average rain event, the driving rain data from all forty
two cities is presented in Figure 7-4. Figure 7-4 illustrates the percentages of driving rain greater
than a given rain rate during a rain event. In all monitored cities, half of all hours of rain were at
an intensity of less than 0.5 – 0.9 mm/hr. This is a small range of driving rain amounts
representative of all cities in Canada and the midway point of the range (0.7 mm/hr) will be used
as the average driving rain rate.
49
Percentage of Time that Hourly Rainfall is Greater than a Given Amount
During Rain Events
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0
1
2
3
4
5
6
7
8
9
10
Driving Rain (mm/hr)
Figure 7-4 : Driving Rain Analysis of 42 Canadian Cities
For the extreme driving rain events, both the 1% and 5% rain events are displayed on Figure
7-5 to determine a representative extreme rain event. The 1% and 5% rain events are the
amounts of rain that fall during rain events, 1% or 5% of the time respectively. There is a much
larger range of rainfall for the extreme rain events representative of different climate areas of
Canada. The 5% rain event ranges from 2.2 to 6.8 mm/hr, and the average line crosses through
4.2 mm/hr. The 1% rain event appears more characteristic of an extreme wetting event, and has
a range of 3.0 to 10.4 mm/hr, and the average line crosses through at 7.5 mm/hr. Since there is
no precedent for which value to use, it was decided to use the limits of the 1% rain event in this
thesis. This will give an indication of the importance of the value chosen for water ingress
calculation, similar to a sensitivity analysis. For the higher value of the 1% rainfall, the amount
was extrapolated from the end of the curve. A summary of the rain values used in the analysis
50
can be found in Table 7-2. All of the rain data used here is assumed to be on the worst wall
orientation regardless of location.
Percentage of Time That Hourly Rainfall is Greater than a Given Amount
During Rain Events
10%
9%
8%
7%
6%
5%
4%
3%
2%
1%
0%
0
1
2
3
4
5
6
7
8
9
10
11
12
Driving Rain (mm/hr)
Figure 7-5 : Extreme Driving Rain Events from Canadian Weather Data
Table 7-2 : Driving Rain Amounts for Case Study
Deficiency
RDF Value
Average Driving 1% Driving Rain 1% Driving Rain
Number
(Figure 7-2)
Rain Event
Minimum
Maximum
1 and 2
1.0
0.7 mm/hr
3 mm/hr
10.4 mm/hr
3 and 4
0.5
0.35 mm/hr
1.5 mm/hr
5.1 mm/hr
It is also important to calculate the wind pressures specifically during rain events, since wind
is often different during rain events. Wind pressures may help drive rain through enclosure
openings as discussed in the moisture physics chapter. For leakage testing, enclosure assemblies
are subjected to induced pressure loads in an effort to imitate realistic loads. The pressure
exerted on a wall by wind is called the stagnation pressure and is calculated by:
51
p = 0.65 ⋅ V 2
(7.5)
0.65 = ½ ρair = ½ 1.29 kg/m3
p = staganation pressure (Pa)
V = wind speed (m/s)
It is important to note that most wind speeds are reported for 10 m above the ground.
Figure 7-6 plots the wind pressures, reported in the same CMHC study, corresponding to rain
events greater than 5.1 mm/hr. The wind data is hourly averages, and does not take into account
individual gusts. The graph shows that for all studied locations in Canada, the wind pressure is
less than 84 Pa 99% of the time during rain greater than 5.1 mm/hr. Note that this value is an
extrapolation of the data given.
Percentage of Time That Hourly Wind Pressure is greater than given wind
pressure during rain > 5.1 mm/hr
20%
18%
16%
14%
12%
10%
8%
6%
4%
2%
0%
0
10
20
30
40
50
60
70
80
90
Wind Pressure (Pa)
Figure 7-6 : Probability of Wind Pressures During Rain Events > 5.1 mm/hr
Some different water penetrations testing standards are shown in Table 7-3. It was shown
previously that 99% of all driving rain in Canada occurs during rain events of less than 10
52
mm/hr. This corresponds to an application rate of 0.17 L/min-m2. The average rain event for the
case study is 0.7 mm/hr or 0.012 L/min-m2. The hourly average wind pressures during rain
events only exceed 84 Pa 1% of the time. From the driving rain and wind pressure data for
Canadian cities, it seems that the testing protocol are excessive, especially if these test methods
were applied to enclosure design in the less extreme areas of Canada. The testing water spray
rates are more than an order of magnitude greater than some of the worst recorded hourly data in
Canada. These testing protocols could indicate that a building technology is not adequate, when
in fact it may be more than adequate in the right climate region. The test protocols also exert
such high wind and rain loads that different types of failures may occur than in the field.
Table 7-3 : Water penetration testing standards (Lacasse et al. 2003)
In all fairness to testing protocol pressures, wind pressures should be calculated at heights
greater than 10m since the wind speed increases with height (Figure 7-7). The National Building
Code of Canada (NBCC 1996) has a standard approach to correct wind speed for changes in
height. The wind speed at any height can be calculated from:
V ( z ) = V10 ⋅ ( z / 10) α
V = wind speed 10 m above grade normally reported by weather stations (m/s),
10
z = height above grade (z) and
α = exposure exponent from Table 7-4
53
(7.6)
Table 7-4 shows the exposure constants that should be used for different areas according to
both the National Building Code of Canada and the American Society of Civil Engineers
(ASCE). The numbers are very similar for similar exposure conditions so the Canadian Building
Code constants will be used for these calculations. The concern with wind pressures is most
common in city centers since there are a greater number of high-rise buildings. Using the ten
meter wind speed of 11 m/s from the 99% wind pressure determined previously, the wind speed
and pressure was calculated at a height of 122 m (400 feet) in a city centre location. The wind
speed was calculated to be 27 m/s corresponding to a pressure of 474 Pa at 122 m in a city
centre. An hourly average wind pressure of 474 Pa occurs 1% of the time during rain at a height
of 122 m. The recalculated wind pressure is much closer to the test standards, and some gusts
exceeding 474 Pa are anticipated. Wind tends to gust meaning higher pressures are likely, but
only for very short periods of time (less than a second). Gusts of 1 second duration exert a
pressure of about 2.5 times the hourly average.
The test standard CAN-A440-M listed in Table 7-3 shows the maximum air pressure testing
value for windows leakage tests. The CSA testing standard for windows CAN/CSA-A440
covers a wide range of test pressures determined by the elevation as well as the geographic
location. Using Tables UG-1 and UG-2 from the testing standard will determine the test wind
pressure for any location in Canada up to a height of 113 m.
Table 7-4 : Wind speed location constants
Exposure Conditions
Exponent α
ASCE-7
City center
1/3.0= 0.33
Suburban
¼.5= 0.22
Open country
1/7= .14
Coastal
1/10= .10
National Building Code of Canada
Open country
1/7= 0.14
Suburban
¼= 0.25
City center
½.8= 0.36
54
600
For same speed at
gradient height
500
Height (m)
400
Open Country
Suburban
City Center
Figure 7-7 : Wind velocity variation with height and location (Straube and Burnett 2005)
7.2.3
Water Ingress
Water ingress is defined as any water that passes the cladding. Water that passes the cladding
may either be stopped by the sheathing or continue into the studspace and interior. Very little
work has been done to determine leakage rates into a wall, in part, because every case is different
and there are so many variables contributing to water leakage. It is incredibly difficult to predict
the amount of leakage accurately. However, using the wind pressure and the water application
rate calculated for the case study, the leakage rates can be estimated. Calculating the leakage
rates are done with the assistance of a National Research Council (NRC) study titled
Experimental Assessment of Water Penetration and Entry into Wood-Frame Wall Specimens.
One of the most complete tests to date was conducted by the Institute for Research in
Construction called MEWS or Moisture management of Exterior Wall Systems. The objective
55
of MEWS Task 6 was to determine the quantity of water entry in relation to climate loads
(Lacasse et al. 2003)
Testing for Task 6 was done on 8 foot square test panels. There were seventeen test wall
panels clad with stucco, EIFS, masonry, and vinyl siding. The walls were tested in the Dynamic
Wind and Wall Test Facility (DWTF) capable of subjecting the test panels to static or dynamic
pressures of over 2 kPa as well as spray rates of up to 8 L/min-m2.
To determine the quantities of water leakage in the test panels certain design deficiencies were
introduced in wall construction. The deficiencies were located in both the first and second layer
of defense, and can be seen in Figure 7-8.
Figure 7-8 : Location of Design Deficiencies (Lacasse et al. 2003)
To determine the rate of water entry, the water needed to be collected at the entry points. This
was accomplished with troughs in the stud space and the drainage gap at the deficiencies.
Knowing the pressure and water application rate while measuring the water leakage will
determine the leakage rate dependant on the external conditions.
Table 7-5 : Maximum water entry L/min at Different Points of Collection is a summary of the
highest leakage rates in L/min at three deficiencies including the electrical outlet (E), ventilation
duct (V) and window (W). These are the same deficiencies as the case study. The leakage
values for E and W are located in the stud space while the leakage value for V is located in the
56
drainage space. This case study is only concerned with water that gets past the cladding (screen)
and into the drainage gap so the values for the ventilation duct are the most relevant to this
analyis. The NRC found that the amounts of water leakage through the ventilation duct and
electrical outlet are similar.
Table 7-5 : Maximum water entry L/min at Different Points of Collection (Lacasse et al. 2003)
Stucco
SR
E
V
W
1
EIFS
1.7
3.4
1.7
3.4
0.086
0.51
0.087
0.33
0.56
0.037
0.254
0.133
0.01
0.272
0.154
0.02
Brick Masonry
1.7
3.4
0.15
0.185
0.17
Siding
1.7
3.4
0.105
0.03
0.0135
0.159
0.062
0.0134
1 - Spray Rate - SR (L/min-m2)
* When Reference is made to wall assembly types (e.g. "Stucco", "EIFS", "Brick Masonry", "Siding") this implies that results
are derived from tests on a limited number of specimens - Inferences are not being made in regard to generic types of wall
assemblies unless specifically stated as such.
The leakage rates reported in Table 7-5 are for extreme wetting tests and are orders of
magnitude higher than the average wetting event determined by analysis of driving rain data.
These rates may provide some indication of design criteria for extreme climates (eg. hurricanes)
and theoretical leakage maximums, but are not suitable for leakage rates of this case study. The
leakage rates range from 30 to 560 mL/min through the ventilation duct and from 10 to 87
mL/min for a window deficiency.
Figure 7-9 shows a correlation between water entry and water application rate for different
static pressures on stucco clad walls as well as an acrylic sheet cladding which was used as a
base case with the same deficiencies built in. Using the calculated correlations for water ingress,
the water entry rates corresponding to calculated driving rain loads need to be interpolated since
the water ingress testing did not test below 1.7 L/m2-min. All the testing water application rates
in this study seem unrealistic, and it’s unclear how to relate these findings to reality. The
calculated rain application rates from Canadian cities correspond to water entry rates less than 10
mL/min according to Figure 7-9, with the assumption that the lines are linear even at low
application rates.
57
Figure 7-9 : Water Entry Rates and Spray Rate at Different Pressures (Lacasse et al. 2003)
Other conclusions found by the NRC in regards to water leakage are;
•
•
•
•
Gravity alone can cause a significant amount of water leakage.
An increase in pressure will, generally increase the amount of water leakage but not in a
proportional and predictable manner. Water application rates are a more predictable way
to increase water leakage rates.
Water entry is dependent on the nature of water deposition at the deficiency, meaning
that the water entry is dependant on more than just water application rate and pressure
difference.
The wall assemblies with a drainage space showed the fewest instances of water
penetration and some of the lowest activity for the moisture sensors.
Based on the MEWS study and other research in the area of water leakage, it’s nearly
impossible to accurately predict the quantity of water leakage. To get measurable amounts of
water leakage during testing, large application rates are necessary. There are a large number of
variables contributing to water leakage rates including application rate, air pressures, and most
importantly design details. Determining the correct order of magnitude of water leakage is
probably sufficient for most analysis and would be easier to determine if realistic water
application rates were used in testing.
58
7.3
Conclusions
The driving rain deposition rate for an average driving rain event for all monitored Canadian
cities was found to be 0.7 mm/hr (0.012 L/m2-min). This was used as the average since half of
all rain in Canada was less than 0.5-0.9 mm/hr. For the extreme rain event, the boundaries of the
1% rain event (occurs 1% of the time during rain) were chosen since no precedent could be
found. The boundary values for the 1% driving rain event are 3.0 mm/hr (0.05 L/m2-min) and
10.4 mm/hr (0.17 L/m2-min). Most common test standards are significantly higher than these
water application rates.
Wind pressures during rain were calculated to be less than 84 Pa 99% of the time at 10m and
less than 474 Pa 99% of the time at 122 m. The test wind pressures are within the same order of
magnitude to wind pressures at 122 m. For testing at lower elevations, test pressures are
unrealistically high.
The water ingress study was conducted with water application rates orders of magnitude
higher than calculated rain events. To achieve measurable amounts of leakage, large application
rates were necessary. Based on the MEWS study and the number of variables contributing to
water ingress, it’s nearly impossible to predict the quantity of water leakage. A better use of
resources would be ensuring that enclosure design details were designed properly.
The MEWS research did prove that gravity alone can cause a significant amount of leakage
and that wall assemblies with a drainage space experienced lower quantities of water ingress.
Combining the water ingress study with the drainage gap analysis, the highest leakage rate of
560 mL/min was compared to theoretical drainage amounts. A 0.5 mm gap is capable of
draining three times the leakage amount over a meter of wall width (1530 mL/min-m). The
leakage rates found in the MEWS testing were a result of unrealistically high application rates.
59
8.0 Drainage and Drying Test Development
In previous sections, theoretical flow rates in gaps, driving rain, and water ingress, have been
investigated to help determine moisture loads in enclosure walls. Field work and laboratory
studies have shown that ventilation drying is an important process for removing enclosure
moisture and increasing the durability of a wall system (Straube 1997, Straube et al. 2004,
Schumacher et al. 2003). These field and laboratory tests did not measure the drainage or
storage capabilities of real wall systems, instead using wetting apparatuses to apply water to
towels in the drainage plane. Determining how much water different wall systems will store is
needed to determine the drying rates required for different wall systems.
The University of Waterloo was commissioned by several manufacturers to characterize the
airflow, drainage and drying behind a range of different cladding systems including, cement
fibreboard, wood and vinyl siding, exterior insulation and finish systems (EIFS) and cement
stucco systems. With no previous experimental testing experience characterizing drainage and
drying, a test method and apparatus were required for this testing.
The goal of the drainage and drying test development is to design a repeatable test method to
quantify the amount of drainage and storage for different wall systems.
8.1
Test Standards
Research into existing test methods returned three relevant test methods to use as resources for
drainage testing; ASTM E514 Standard Test Method for Water Penetration and Leakage
Through Masonry, ASTM E331 Standard Test Method for Water Penetration of Exterior
Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference, and
ASTM E2273-03 Standard Test Method for Determining the Drainage Efficiency of Exterior
Insulation and Finish Systems (EIFS) Clad Wall Assemblies.
ASTM E331 uses a spray grid to evenly distribute a minimum spray rate of 3.4 L/m2-min
across the exterior surface of the test area. This seems like a high spray rate consistent with the
60
test methods seen in Table 7-3 previously.
This test is designed more to test the water
penetration of a cladding rather than the drainage of a cladding system.
ASTM E2273 uses a spray rate in accordance with the E331 standard to determine the
drainage efficiency of EIFS clad wall systems. Testing is conducted with two calibrated spray
nozzles directed into a 24 inch by 2 inch opening through the cladding on to the water resistant
barrier. The test runs for 75 minutes allowing between 7950 and 8725 g of water to enter the
drainage plane. This test standard explains how to calculate the EIFS clad wall system assembly
drainage efficiency using a ratio of the known water added to the measured water drained. One
issue with this test method is that there is no indication of whether or not the drainage efficiency
is acceptable, nor why almost any wall system would not drain more than 95% of such a high
amount of water. The volume of test water seems quite large considering the surfaces of the
drainage gap are generally designed to be nonabsorptive.
The third relevant test method is ASTM E514, Standard Test Method for Water Penetration
and Leakage through Masonry.
The masonry test requires 138 L/m2-hr which is equivalent to
2.3 L/min-m2. Not only is this a high application rate, the test requires that it continue for a
minimum of four hours. Since brick veneers are essentially transparent to water, and water will
generally pass through the veneer in under a minute (Lstiburek 2003), this water penetration test
will also test the drainage capabilities of the drainage gap.
The relevant test standard application rates and pressures are summarized in Table 8-1 along
with the values calculated for average and extreme driving rain events in Canada to compare the
test methods with realistic water application rates.
Table 8-1 :Comparison of Test Standards to Calculated Rain Loads
ASTM E 514
ASTM E 331
Calculated Average
Rain Event (Chapter 6)
Calculated Extreme
Rain Event (Chapter 6)
Water Application Rate
(L/min-m2)
2.3
3.4
Pressure (Pa)
500
137
0.012
10 (calculated at 10m)
0.17
84 (calculated at 10m)
61
Table 8-1 shows that the standard test method application rates for ASTM E514 and E331 are
two orders of magnitude higher than average driving rainfall rates for all of Canada, and one
order of magnitude greater than 99% of all driving rain events in Canada. The pressures for the
standard tests are much greater than calculated wind pressures during rain events for both the
average and extreme events. It is unclear how these application rates were chosen and whether
the test methods were designed to represent realistic application rates.
Another standard relevant to drainage and storage testing is a Canadian Construction Materials
Centre (CCMC) standard for stored water in EIFS. This standard is currently still under revision
and is intended to classify EIFS adhered to wood substrates based on their moisture storage after
drainage and 24 hours of drying. The standard states, at the time this research was conducted,
that the moisture retained at the end of a wetting/drainage phase lasting two hours to be no
greater than 30 g/m2 and that the retained moisture after two full days of drying be no greater
than 15 g/m2. These standards are currently under review but will be more closely analyzed later
in this chapter and compared to storage results from experimental drainage testing.
8.2
Previous Test Methods
There was only one study found that quantitatively measured drying in a wall system. A
ventilation drying study was conducted at Penn State University (PSU), measuring the
effectiveness of different size gaps to drying (Schumacher et al. 2003). The wall was constantly
monitored with the use of a load cell and counterbalance weights to limit the load on the load cell
and increase the precision of the load cell (Figure 8-1).
62
Figure 8-1 : Test Apparatus for Ventilation Drying Study (Schumacher et al. 2003)
The study concluded that ventilation airflow can remove significant amounts of moisture and
that the diffusive component to drying is much less. It was also shown in Figure 8-2 that there is
a correlation between airflow rate (L/s) and the time required for drying (Schumacher et al.
2003). This study was used to help design the test apparatus for research in Waterloo.
63
Figure 8-2 : Test Results for Ventilation Drying Study (Shumacher et al. 2003)
A detailed study of qualitative drainage testing was conducted on seven wall panels with vinyl
siding and seven wall panels clad with stucco (Straube et al. 2000). Viewports were cut in the
sheathing and sheathing membrane in the back of each wall to observe the drainage performance.
Four different test procedures were used to apply water to the vinyl siding. Water was applied
to the face of the siding with the use of a hose with and without a pressure difference across the
wall, and water was poured behind the vinyl siding with and without a pressure difference across
the wall. In some testing, pressure was induced across the walls with a blower door in the
building entrance.
It was found by Straube et al. (2000) that the water applied to the surface of the siding leaves
predominantly through the j-trim and that water poured behind the siding is caught by the
horizontal edges in the siding and directed to the j-trim to be drained. It was concluded that
significant areas of the drainage plane were not wetted with either water application method.
The testing procedure for the stucco test walls consisted of pouring two litres of water behind
the stucco. It was found that single layers of sheathing membrane bonded to the stucco and did
not drain well. Stucco bonded to the sheathing membrane behaves like a perfect barrier wall
64
system and may experience durability issues, similar to common building enclosure failures in
British Columbia. It was found that by adding an extra layer of sheathing membrane, water
drained far better than a single layer even if the single layer was corrugated (Straube et al. 2000).
Stucco bonded best to the housewrap and water repellency was lost resulting in the worst
performing system. The corrugated housewrap also performed poorly when installed directly
behind stucco since the stucco bonded to the surface of the housewrap and eliminated the
drainage space. However, when used in a system with felt paper between it and the stucco, it
was the best performing system (Lstiburek 2003).
Quantitative Testing was also being done by Forintek Canada Corp for a group of building
product manufacturer for a greater understanding of EIFS. This testing was started in May 2004
and was conducted following the drainage test method specified in the CCMC Technical Guide
for EIFS systems on wood substrates.
The test setup employed by Forintek used a balance to monitor the wall gravimetrically during
the entire testing procedure.
It was modeled after the test apparatus used at Penn State.
Approximately 8 L of water was applied to the drainage space in one hour. All three of the EIFS
walls tested by Forintek had much higher values for 2 hour and 48 hour storage limits than
allowed by the CCMC criterion. Also noted was that there was a significant difference in the
storage values between identically constructed walls (126 – 254 g/m2). This could either have
been caused by differences in construction of all three test walls, or by the test apparatus. During
the drying phase of the testing, the wall cavities were left open, which may have influenced the
drying capability, and overestimated the drying potential of the cladding system.
8.3
Test Development
From the previous testing, it was clear that a precise and reasonably accurate method of
measuring the moisture content of test walls would be needed to understand the drainage and
drying characteristics of wall systems. The PSU and Forintek work showed that a controlled RH
environment is important, so it was decided that testing would take place in the BEGHut
laboratory. This lab is controlled to approximately 20ºC/50%RH.
65
The method of gravimetrically quantifying the amount of water stored in the wall for this
thesis was based on the test apparatus used in the ventilation drying study at Penn State
University (Figure 8-1). One change that was made in an attempt to improve the test apparatus
was to change the load cell from compression to tension. Subjecting the load cell to tension was
done to simplify the test setup, allow many different wall sizes, and to minimize lateral loads on
the load cell. A schematic of the test apparatus developed for this research is shown in Figure
8-3.
A drainage trough was attached to the top of the wall and a collection trough at the bottom
directed to a storage bucket, both made from aluminum sheet.
66
Figure 8-3 : Testing Apparatus
A second load cell was used to measure the drained water collected in the water bucket.
Originally, a water storage device was attached to the ceiling and designed to maintain a constant
head in the water drainage trough. Much time and effort was spent designing the constant head
apparatus, suspending it from the ceiling, and connecting a load cell to it, but during the
commissioning test it was found that water could not be introduced into the drainage trough
quickly enough to maintain head pressure, even at high rates. The constant head apparatus was
abandoned in favor of manually pouring a known amount of water into the drainage trough over
67
a fixed period of time. A photograph of the test setup and balance are shown below in Figure
8-4.
Figure 8-4 : Photograph of Testing Apparatus
The first experimental program was conducted to characterize both EIFS wall systems and
some traditional stucco systems (Karagiozis et al. 2004). These walls were constructed by the
manufacturer and shipped to the University of Waterloo for testing. The test walls were four feet
wide, and eight feet tall with a seven foot tall test section (Figure 8-5).
68
4'-0"
Top and bottom
horizontal edges as
in normal practice
7'-0"
8'-0"
Joints in
DensGlas
4'x7' test section
6"
Single top &
bottom track,
20 ga stud
Edge details as in
practise, flush
with studs
Peel and stick covers
vertical edges
Figure 8-5 : Test Wall Construction
It was decided, in part based on ASTM E2273, to use eight litres of water for drainage testing
since there were no other precedents found for test volumes. This required two four litre
containers of water poured into the drainage trough.
The drainage graph from the
commissioning test is shown below in Figure 8-6. The total water accounted for at the end of the
test by combining the stored water and the drained water was approximately 2500g, the
remaining water ended up on the floor of the lab. This was because the collection trough was
much too small to handle the high rate of water exiting the wall meaning that either the volume
of water or the flow rate needed to be decreased. There was a small gap in time (visible on the
graph) caused by switching water containers during water application. In this time gap, the wall
appears to equilibrate to approximately 500g of storage. After the second container of water, the
wall also equilibrated to approximately 500g of storage.
69
Some important conclusions about drainage testing were learned from the commissioning test.
For the commissioning test wall, it appeared that regardless of how much water was put in the
drainage cavity, the storage would be approximately 500g, meaning that the maximum storage
had been achieved. This was a consideration for all subsequent testing. Also, the results showed
the volume of applied water could be decreased from 8 litres for small storage volumes with no
change in the results of the test.
3500
Stored Water
Drained Water
3000
Mass of Water (g)
2500
2000
1500
1000
500
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Time (minutes)
Figure 8-6 : Commissioning Test Results
The final drainage test protocol for the first set of wall tests consisted of:
1. Calibration check of load cells ( a known load is applied to the test wall and the reading
from the balance is confirmed)
2. 1.5 litres is poured into drainage cavity over one minute
3. Fifteen minutes is waited to allow drainage to finish
4. A second 1.5 litres is poured into the drainage cavity over one minute
5. Waiting fifteen minutes for drainage to finish
6. Begin Drying Test
During the first test program, many extra tests were undertaken to better understand the
drainage and drying analysis and to determine the best methods for testing.
In the commissioning test, the back of the sheathing was open to the lab. It was suspected that
this had an impact on the drying capability of the wall, especially since the gap was small,
allowing for little ventilation drying and the permeance of the cladding was low. Foil faced
70
polyisocyanurate (polyiso) was taped to the steel studs with aluminum tape against the back of
the sheathing providing both an air and vapour barrier to limit drying to the front of the wall
systems. The results of comparison tests with and without the polyiso are shown below in Figure
8-7.
250
200
Drying with polyiso
Drying without polyiso
Mass of Water (g)
150
100
50
0
-50
0
24
48
72
96
120
Time (hours)
Figure 8-7 : Comparison of Drying With and Without Polyisocyanurate Sealing the Studspace
The polyiso greatly slowed the drying of the wall system. Using polyiso in the studspaces
gave a better indication of cladding and drainage gap performance, so all subsequent drying tests
were conducted with polyiso sealed with aluminum tape to prevent vapour diffusion and air
leakage through the back of the wall.
To closer simulate real world results, a fan was used to simulate average wind pressures as
found in laboratory studies previously conducted by the Building Engineering Group (Straube
and Burnett 1998). The pressure was measured across the surface of the cladding between the
bottom and the top of the drainage gap. A pressure difference between top and bottom of one
pascal was induced using a fan and measured with a DG700 digital low pressure manometer
71
from the Energy Conservatory. This was done with the averaging capability built in to the
manometer to smooth out the dynamic variations in the pressure. The fan was adjusted and
measurements were taken until a ten second average of approximately 1 Pa was achieved.
A pressure of 1 Pa was found to have a noticeable affect on the drying of test walls even with a
small gap. Figure 8-8 shows the difference in drying potential with a fan on a wall system with
an equivalent gap size of less than 2 mm, and a very low permeance cladding material. The
equivalent gap size was determined by airflow testing. Airflow testing is beyond the scope of
this thesis but the test procedure is summarized in the appendix.
250
200
Drying with fan
Drying without fan
Mass of water (g)
150
100
50
0
-50
0
24
48
72
96
120
Time (hours)
Figure 8-8 : Comparison of Drying With and Without Simulated Wind Pressure
As can be seen in the previous figures, the drying curves for the wall systems are not perfectly
smooth. They can vary up to five grams while still maintaining a drying trend, or as they reach
equilibrium (ie. “dry”) the measured water content may still fluctuate. At first it was thought this
was some error in reading or measuring, but then the laboratory RH was compared to the drying
72
curves and it was found that there was a correlation between the laboratory RH and the
fluctuations in the drying curves (Figure 8-9).
200
70
Stored Water
BEGhut RH
60
50
100
40
RH (%)
Mass of Water (g)
150
50
30
0
20
-50
10
0
24
48
72
96
120
Time (hours)
Figure 8-9 : Effects on Testing from Changes in Laboratory RH
These results show the sensitivity of the balance and measurement system to the change in
mass of water stored in hygroscopic materials in the wall system. Ideally, the volume of
hygroscopic materials should be limited by methods such as using steel studs instead of wood
where possible.
After conducting several drainage tests, it was unclear how much moisture was absorbed into
the building materials, and how much moisture was stored on the surfaces of materials by surface
tension. To gain a better understanding of moisture storage, three tests were done testing the
storage capacity of nonabsorptive materials.
8.3.1
Plexiglas and Polyethylene Sheet Testing
A sheet of polyethylene approximately 7’ by 4’ was suspended on the front of a wall system.
The plastic sheet was sprayed with water until the maximum surface storage was reached. Three
tests all showed that the approximate total storage was 100g, equivalent to 35 g/m2. The poly
73
was not perfectly smooth, and it was attached at several points such that the surface was
irregular. All of the excess water from the spraying drained into a storage container on the floor.
Tests were also conducted on a wall system constructed of plexiglas as explained previously.
The drainage test in the plexiglas wall was performed twice, and the repeatable storage amounts
in the drainage gap are shown in Table 8-2.
Table 8-2 : Results of Drainage and Storage Testing on a Plexiglas Wall System
Plexi-1
Plexi-2
Drainage Plane
Cladding
Estimated
Drain Gap
(g/m2)
primary
(g/m2)
secondary
plexiglas sheet
plexiglas sheet
plexiglas sheet
plexiglas sheet
1 mm
1 mm
24
21
25
23
Another fan comparison was conducted on a drainage gap constructed of two sheets of
plexiglas, completely eliminating absorption and diffusion through the front and back of the gap.
The gap width was difficult to maintain across the width since plexiglas is flexible, but washers
were used as spacers at 21 locations between the two sheets of plexiglas, estimating an
equivalent gap width of 1 mm. Figure 8-10 shows that even in such a small gap, with zero
diffusion inward or outward, drying with a fan (ie. ventilation drying) is still effective.
74
40
35
Mass of Water (g)
30
25
20
Test B - no fan
15
10
Test C - fan
5
0
0
10
20
30
40
50
60
70
80
Time (hours)
Figure 8-10 : Effect of Fan on Drying of Plexiglas Wall System
Another test done was conducted on a sheet of plexiglas similar to the polyethylene sheet test
to help understand why less water was stored in the gap than on the surface of the polyethylene
sheet. It was found using a similar procedure that the plexiglas single sheet stored approximately
65 g/m2 of water. The plexiglas stored close to twice the amount of the polyethylene sheet. This
was likely caused by differences in surface characteristics, and hydrophobicity.
The single sheet of plexiglas stored considerably more water than the plexiglas drainage gap.
It was easier to uniformly wet the single sheet and the beads of water formed on the surface of
the plexiglas were larger (approximately 3-4 mm) than the gap in the plexiglas wall. This means
that the plexiglas drainage gap was not capable of storing as much water since the gap was too
narrow for the beads of water to form.
Comparing the storage amounts of hydrophobic nonabsorptive materials to the tentative
CCMC values, the poly storage was greater, and the plexiglas wall was only slightly lower. This
shows that even in completely nonabsorptive, hydrophobic materials, it’s difficult to achieve the
current performance standard set by the CCMC in 2004.
75
8.4
Conclusions
The amount of drainage in the commissioning test wall was surprising since the gap was
barely visible and calculated to be equivalent to approximately 2 mm in width by airflow testing.
Tests were done to determine the effects of a sealing the back of the sheathing, and using a fan
to help with ventilation drying. It was found that sealing the sheathing with polyiso slowed the
drying rate considerably in the commissioning test wall. Drying with a fan increased the rate of
initial drying in both comparison tests conducted during test development.
During testing of non absorptive materials, a suspended polyethylene sheet consistently stored
35 g/m2 and a single sheet of plexiglas stored 65 g/m2. The drainage tests in the plexiglas wall
resulted in storage amounts of approximately 24 g/m2.
A test method was developed and can be found on page 69.
76
9.0 Drainage and Drying Test Program
9.1
Test program
The goal of the test program is to determine drainage and storage capabilities of different wall
systems using the repeatable test procedure developed in the previous chapter.
Two main categories of walls were chosen for testing. The first category includes walls with a
continuous drainage gap over the entire height of the wall. This means that water that enters the
top and drainage can only occur at the bottom (Table 9-1). The second category includes walls
constructed with siding having a discontinuous drainage gap. Such gaps are designed to drain
over the entire surface area of the wall so drainage will not only occur at the bottom (Table 9-2).
The three main variables examined during testing are the drainage gap width, the drainage
plane material, and the cladding material. The drainage plane material and cladding generally
form the surfaces of the drainage gap. The drainage gap materials are shown in the test matrices
and the drainage gap width is shown if the equivalent gap was determined with airflow testing.
In some cases, the wall sizes for the drainage testing were 3’ x 7’ frames (instead of 4’x8’)
with a 3’ x 6’ test area so they would be easier to handle in the lab. The water application was
changed to 1 L per test for these walls. Storage amounts were always reported in g/m2, so the
test areas are normalized. All other aspects of the previously reported test procedure were kept
the same.
77
Table 9-1 : Test Matrix for Continuous Drainage Gap Assemblies
System
Test
Drainage Plane
Cladding
Gap
(mm)
Gap
EIFS-1
Test 3
Test 4
Test 5
Test 6
DensGlas Gold
DensGlas Gold
DensGlas Gold
DensGlas Gold
EPS with ext. finish
EPS with ext. finish
EPS with ext. finish
EPS with ext. finish
>1
>1
>1
>1
formed by adhesive
formed by adhesive
formed by adhesive
formed by adhesive
EIFS-2
Test 1
trowel applied
EPS with ext. finish
1.5
formed by adhesive
EIFS-3
Test 1
Test 2
trowel applied
trowel applied
EPS with ext. finish
EPS with ext. finish
<1
<1
1/4" by 1" grooves
1/4" by 1" grooves
EIFS-4
Test 2
Test 3
trowel applied
trowel applied
EPS with ext. finish
EPS with ext. finish
3
3
formed by adhesive
formed by adhesive
EIFS-5
Test 1
Test 2
Test 3
Test 4
trowel applied
trowel applied
trowel applied
trowel applied
EPS with ext. finish
EPS with ext. finish
EPS with ext. finish
EPS with ext. finish
2
2
2
2
formed by adhesive
formed by adhesive
formed by adhesive
formed by adhesive
EIFS-6
Test 3
Test 4
Test 5
Tyvek
Tyvek
Tyvek
EPS with cement coating
EPS with cement coating
EPS with cement coating
Stucco-1
Test 2
Test 3
2 layers #15 felt
2 layers #15 felt
3/4" Cement Stucco
3/4" Cement Stucco
<1
<1
2 layers #15 felt
2 layers #15 felt
Stucco-2
Test 1
Test 2
2 layers #15 felt
2 layers #15 felt
3/4" Cement Stucco
3/4" Cement Stucco
9
9
19 mm strapping
19 mm strapping
AGM-1
AGM-1
Test 1
Test 2
Air Gap Membrane
Air Gap Membrane
Vinyl siding
Vinyl siding
3
3
Felt-1
Felt-1
Test 1
Test 2
#15 paper
#15 Paper
Vinyl siding
Vinyl siding
Towel-1
Towel-2
Test 1
Test 1
Air Gap Membrane
#15 Paper
fiber cement (paper towels)
fiber cement (paper towels)
polyethylene sheet
none
Poly-1
Plexi-1
Plexi-1
Plexi-2
Test 1
Test 2
Test 1
plexiglas sheet
plexiglas sheet
plexiglas sheet
plexiglas sheet
plexiglas sheet
none
FCSheet-1
FCSheet-1
FCSheet-1
FCSheet-2
FCSheet-2
FCSheet-2
Test 1
Test 2
Test 3
Test 1
Test 2
Test 3
Tyvek
Tyvek
Tyvek
Tyvek
Tyvek
Tyvek
Fiber cement Sheet
Fiber cement Sheet
Fiber cement Sheet
Fiber cement Sheet
Fiber cement Sheet
Fiber cement Sheet
FCSheet-3
FCSheet-4
Test 1
Test 1
Tyvek
Tyvek
Fiber cement Sheet
Fiber cement Sheet
FCSheet-5
Test 1
Tyvek
Fiber cement Sheet
78
horiz and vert grooves
horiz and vert grooves
horiz and vert grooves
3
<1
∞
approx 1 mm
approx 1 mm
∞
Table 9-2 : Test Matrix for Discontinuous Drainage Gap Assemblies
System
Test
Drainage Plane
Cladding
Vinyl Siding
Vinyl-1
Vinyl-1
Vinyl-1
Test 4
Test 2
Test 5
Tyvek
Tyvek
Tyvek
Vinyl siding
Vinyl siding
Vinyl siding
Vinyl-2
Vinyl-2
Vinyl-2
Test 11
Test 9
Test 7
#15 Felt Paper
#15 Felt Paper
#15 Felt Paper
Vinyl siding
Vinyl siding
Vinyl siding
Tyvek
Tyvek
Tyvek
Back primed fiber cement
Back primed fiber cement
Back primed fiber cement
Fiber Cement Siding
FCSiding-1
Test 10
FCSiding-1
Test 8
FCSiding-1
Test 6
9.2
9.2.1
FCSiding-2
FCSiding-2
Test 16
Test 14
#15 Felt Paper
#15 Felt Paper
Back primed fiber cement
Back primed fiber cement
Cedar Siding
Cedar-1
Cedar-1
Test 13
Test 12
Tyvek
Tyvek
Cedar Siding Untreated
Cedar Siding Untreated
LP Smartside
LP-1
Test 17
LP-1
Test 15
Tyvek
Tyvek
LP Smartside
LP Smartside
Drainage and Drying Results – Continuous Drainage Gap
EIFS Testing
Table 9-3 shows the storage amounts for the EIFS test walls 1-5. The tests that did not follow
the exact protocol were given different amounts of time to finish drainage. Less than fifteen
minutes was used to equilibrate between pours or before starting the drying test. Construction
details of all the EFS test walls are shown in Figure 9-1. EIFS-1, EIFS-2, EIFS-4 and EIFS-5
were all constructed similarly, and had the lowest storage amounts of the five EIFS walls.
79
Table 9-3 : Results from EIFS Drainage Testing
Wall
EIFS-1
EIFS-1
EIFS-2
EIFS-3
EIFS-3
EIFS-4
EIFS-4
EIFS-5
EIFS-5
EIFS-5
EIFS-5
Initial Storage Final Storage
Test Number
(g/m2)
(g/m2)
1*
88
77
2*
85
81
1
133
160
1
186
200
2
194
208
1*
108
119
2
111
135
1
48
75
2
45
69
3
50
80
4
43
68
* does not follow the exact experimental protocol
Percentage
Increase
-13%
-5%
20%
8%
7%
11%
21%
56%
53%
61%
58%
EIFS-1 and EIFS-5 had the lowest storage values of the four similarly constructed test walls.
EIFS-1 was the only wall constructed without a trowel applied drainage plane, indicating that the
air and vapour barrier used in EIFS-2 and EIFS-4 may absorb significant amounts of water.
EIFS-5 used a different formulation of trowel applied drainage plane showing that the type of
drainage plane used will affect water storage. The drainage plane for EIFS-5 absorbed a similar
amount as the untreated OSB drainage plane of EIFS-1.
EIFS-3 and EIFS-4 contain one and two starter strips respectively. A starter strip is simply a
piece of corrugated plastic 3 mm thick installed at the top and/or the bottom of the cladding.
This is designed to allow more drainage, but no significant difference in drainage was observed.
EIFS-3 stored more moisture than EIFS-1, EIFS-2, EIFS-4, and EIFS-5 because of the
increased surface area of the grooved drainage plane, as well as the drainage track and granular
vent assembly. The drainage track, if not properly installed could trap water.
It is interesting to note that when the storage amount of EIFS 1-5 are compared with the
tentative CCMC standards discussed previously, all of the walls, are considerably higher than the
30 g/m2 limit.
80
Figure 9-1 : EIFS Wall Drawings
81
The reason EIFS 1 stored more water in the first pour than the second pour is likely because
fifteen minutes were not left between pours and after the second pour. In the original test
method, as soon as the drainage appeared to have stopped, the measurements were taken. In this
case drainage may not have been complete.
It was found that all EIFS test walls drained very quickly and that the amount of water retained
was very repeatable in all cases.
In the drying phase of the testing the interpretation of results was more difficult.
The
temperature and RH in the lab were kept fairly constant at 50% RH and 20ºC. Any changes in
lab conditions could potentially affect the drying rates of the wall systems. Wall one was tested
twice with identical drying conditions to confirm repeatability and was found to have repeatable
drying performance (Figure 9-2). There were some problems with the data logger and resolution
of the data being recorded which is the reason for the difference in the appearance of the EIFS-1
Test 5 curve.
250
200
Mass of Water (g)
EIFS-1 Test 6
EIFS-1 Test 5
150
100
50
0
0
20
40
60
80
Time (hours)
Figure 9-2 : Repeatability of Drying Results
82
100
120
Figure 9-2 shows two distinct drying rates associated with the drying of the drainage cavity.
There was a preliminary drying rate which has a steeper slope, and a secondary drying rate
which is shown by a much more gradual slope. The high preliminary drying rate may be caused
by water that evaporates from wall surfaces stored by surface tension. Drying of surface water
will happen relatively quickly (even more quickly with fan-forced ventilation). The second
drying rate is assumed to be dependant on moisture redistribution inside the wall materials, the
permeability of the cladding material, and the rate and quality of ventilation.
One of the factors controlling the moisture storage in EIFS systems is the construction
technique, specifically adhesive application. This means it is possible to test the same wall
configuration in two different wall panels and observe different storage and drying performance.
This may have been the reason for the large variation in readings from the Forintek testing
results. If the adhesive is applied in horizontal lines instead of vertical for example, much more
water would be stored and drainage would be eliminated.
It appears from the percentage increases in the mass of the stored water that EIFS-5 may have
been able to store more water had it undergone more wetting. This may have been caused by
changes in the physical characteristics of the trowel applied layer after wetting, since it is
unlikely that the EPS foam was absorbing significantly more moisture with subsequent wettings.
After the testing had concluded the wall was disassembled to observe the drainage path. It can
be seen from Figure 9-3, that the entire surface of the wall was not wetted during the last
drainage test when dye was added to the water. The increasing mass of water between tests
could have been due to an increased area of wetting, but it would be difficult to achieve such
repeatable results if the increases were based solely on wetting area since the locations of the
wetted areas is not predictable.
83
Figure 9-3 : Drainage Patterns in EIFS-5 Wall
Comparing the drainage pattern to the flow visualization drainage patterns from Figures 9-14 and 9-15,
it appears that in some channels the drainage plane is hydrophobic, causing narrow defined drainage
paths, but in other areas, the entire surface seems uniformly wetted similar to an absorbent surface. This
could be caused by differential distribution of drained water, but it can not be determined conclusively
from the tests that were conducted.
84
The drying curves for EIFS wall 5 were very similar in shape to the drying curves for walls 14, with a higher preliminary drying rate, and a lower secondary drying rate. Half of all stored
water was lost in the first 50 hours.
9.2.2
Grooved EIFS Testing
Testing was also conducted for a unique cladding system (EIFS-6), similar to an EIFS
cladding but with grooves in the back of the EPS foam specifically designed to allow for
drainage and drying (Figure 9-4).
Figure 9-4 : Drainage Gap of Grooved EIFS Wall Panel
The system drained very well and the storage values are shown below which are similar to
storage values for the EIFS 1-5. Flow visualization testing on EIFS-6 showed that water was
trapped between the foam and sheathing as well as in the grooves on the back of the EPS foam.
85
Table 9-4 : Drainage Test Results of Grooved EIFS Panel
Wall
EIFS-6
EIFS-6
EIFS-6
Test Number
3
4
5
Initial Storage
(g/m2)
96
90
102
Final Storage
(g/m2)
132
118
144
Percentage
Increase
38%
30%
40%
For EIFS-6, Test 5 used fan-forced ventilation drying and Test 4 was natural drying. In the
first 20 hours with ventilation drying, Test 5 lost 130 g of water. Test 4, with natural drying,
only lost 50 grams of water in the first 20 hours. This shows that ventilation drying is an
effective method of moving moisture out of the wall system for EIFS-6.
9.2.3
Stucco Wall Testing
Stucco-1 and Stucco-2 were constructed with #15 felt drainage layers and ¾” cement stucco
(Figure 9-5). Stucco-2 was built with 19 mm strapping but the space was almost closed off
between the strapping resulting in an equivalent cavity, found by air testing, of only 9 mm.
Figure 9-5 : Stucco Wall System Construction
In Stucco-1, the stucco installation pinched the felt paper so tight that drainage did not occur.
A metal strip was inserted between the layers of felt to open a drainage gap. This only restricted
drainage at the trim and did not affect drainage in the field of the panel. The percentage
increases in the stucco walls were likely caused by the changes in physical characteristics of the
86
felt after wetting. Also, there was an increase in storage quantities from Test 1 to Test 2 for both
Stucco walls, which could have been influenced by the previous wetting of the building paper.
Table 9-5 : Drainage Test Results of Stucco Wall System
Wall
Test Number
Stucco-1
1
Stucco-1
2
Stucco-2
1
Stucco-2
2
Initial Storage
(g/m2)
212
262
189
242
Final Storage
(g/m2)
300
375
245
371
Percentage
Increase
42%
43%
29%
53%
The permeability of the cladding is more critical in walls that are unvented or have very small
gaps, since ventilation drying has a greater influence on drying than diffusion through the
cladding material. This influence was seen in Stucco-2, the only wall with a ventilation cavity
on strapping, which had the highest preliminary drying rate of all tested walls (Figure 9-6).
1200
1000
Mass of Water (g)
Stucco-2
Stucco-1
800
600
400
200
0
0
24
48
72
96
120
Time (hours)
Figure 9-6 : Comparison of Drying for Stucco-1 and Stucco-2
Figure 9-6 compares the drying rates with fan-forced ventilation for Stucco-1 and Stucco-2.
Stucco-2 dried to approximately 650 grams in the first 24 hours and Stucco-1 required 72 hours
to reach the same level of drying illustrating the effect of ventilation on the initial drying with a
drainage (ventilation) gap. The slopes of the drying curves appear very similar between 72 hours
87
and 120 hours indicating that the rate of drying is similar once the preliminary drying is finished
and the remaining moisture is distributed in the wall materials.
9.2.4
Fiber Cement Sheet Testing
Some drainage testing was conducted in conjunction with another testing lab in Fontana,
California to attempt to duplicate drainage and storage results using a different test apparatus.
The balance in Fontana was built identically to the balance at the University of Waterloo, but
unfortunately the laboratory conditions could not be controlled, so only drainage tests were
conducted, since laboratory RH and temperature can have significant effects on the drying rate.
Drainage tests were conducted with fiber cement sheets of three different sizes in an attempt to
find a correlation between the size of wall and the amount of water stored. Test walls were
constructed with New Zealand construction techniques meaning a housewrap was directly
applied to the studs, without the use of sheathing. Blocking is used in New Zealand walls as
lateral bracing instead of sheathing (Figure 9-7).
Figure 9-7 : New Zealand Style Construction with no Sheathing
88
All of the test results are shown below in Table 9-6 with the primary and secondary storage
values from testing in both Waterloo and Fontana. There are large differences between the
primary and secondary storage amounts indicating that the walls had not reached their maximum
storage.
Table 9-6 : Fiber Cement Sheet Testing at Different Locations
Wall
FCSheet-1
FCSheet-1
FCSheet-1
FCSheet-2
FCSheet-2
FCSheet-2
Test Number
Test 1
Test 2
Test 3
Test 1
Test 2
Test 3
Test Location
Waterloo
Waterloo
Waterloo
Fontana
Fontana
Fontana
Initial Storage
(g/m2)
223
232
245
201
228
229
Final Storage
(g/m2)
378
393
411
344
382
400
Percentage
Increase
70%
69%
68%
71%
68%
74%
FCSheet-3
FCSheet-4
Test 1
Test 1
Waterloo
Fontana
218
204
353
364
62%
79%
FCSheet-5
Test 1
Fontana
199
335
68%
Figure 9-8 shows that the test results at both locations are repeatable. The first drainage test
conducted in Fontana was on a 4’x8’ wall (grey line) and while it is similar, it does not appear to
match the other test data perfectly. This was likely due to problems with the balance that were
corrected shortly following the test. Except for that first test, all of the results from tests on the
4’x8’ wall and on the 4’x4’ wall were nearly identical in both locations.
The data in Table 9-6 shows slightly decreasing storage amounts per unit surface area as the
test wall size decreases making it difficult to determine a constant storage amount per area for
this material. However, these results also show that by decreasing the test specimen size slightly
(from 4’x7’ to 3’x6’) the storage values are unlikely to change significantly. No correlation
could be found between moisture stored and surface area, width or height of the test wall.
89
1600
1400
4'x8' Test Walls
Mass of Water (g)
1200
1000
800
600
4'x4' Test Walls
400
200
0
0
5
10
15
Time (min)
20
25
30
Figure 9-8 : Drainage Test Results for Various Size Test Walls in Waterloo and Fontana
One of the concerns with testing the New Zealand style wall was the difficulty of correlating
the amount stored to the surface area because of the non uniformity of the drainage gap. It is
suspected that the blocking may block drainage causing a build up head in the drainage gap
leading to increased storage per width of wall. Figure 9-9 shows an example of the head formed
above the lateral blocking in the wall system. In this case the head formed was enough to
produce a failure in the housewrap. Every 10 mm of water is equivalent to 100 Pa which can
drive water through small holes.
90
Figure 9-9 : Leaking Housewrap
Drainage tests were conducted with dye to determine whether the New Zealand style wall
resulted in higher storage amounts at the blocking. This testing was conducted on two 2’x4’
walls with different types of fiber cement sheet. One of the sheets was designed to be less
absorbent, and the other sheet was more absorbent. On the left in Figure 9-10 is the more
absorbent cladding and on the right is the less absorbent cladding. The less absorbent cladding
clearly shoes the accumulation of dye above the blocking in the wall system. It is much more
difficult to see the accumulation caused by blocking in the more absorbent cladding because of
the uniform distribution of moisture. Non uniform storage caused by blocking is only slightly
visible in the cladding on the left.
91
Figure 9-10 : Comparison of Cladding
The angled pattern of dye exposure in the less absorbent sheet was caused by slight wrinkles in
the Tyvek. It was not expected that the slight wrinkles would have such a significant effect on
drainage. In this case the wrinkles direct almost all the water to the right side of the wall. This
could be critical in wall systems if the housewrap directs water towards a design deficiency.
9.2.5
Air Gap Membrane Testing
Testing was also conducted on a unique dimpled air gap membrane (AGM) intended to replace
current products such as housewrap and building paper. The product is much more durable than
current products and is completely capillary inactive and vapour impermeable (Straube and
Smegal 2005). A concern with the product is that because it is vapour impermeable, it must
allow airflow behind the AGM to allow wall drying. AGM-1 was compared to a typical vinyl
clad wall (Felt-1) with #15 felt as the drainage plane. The wall construction for AGM-1 and
Felt-1 is shown in Figure 9-11.
92
Figure 9-11 : Air Gap Membrane Test Drawings
The air gap membrane tests used two different drying mechanisms: a fan simulating wind
pressure, and two 500 Watt halogen lights simulating solar energy. The goal of the testing was
to compare the performance results of the air gap membrane to commonly used #15 felt paper.
Table 9-7 : Drainage Results for Air Gap Membrane Testing
Wall
AGM-1
AGM-1
Test Number
Test 1
Test 2
Drainage Plane
AGM
AGM
Cladding
Vinyl siding
Vinyl siding
Initial Storage
(g/m2)
141
142
Final Storage
(g/m2)
173
167
Percentage
Increase
23%
18%
Felt-1
Felt-1
Test 1
Test 2
#15 Felt Paper
#15 Felt Paper
Vinyl siding
Vinyl siding
153
161
182
203
20%
26%
Towel-1
Towel-2
Test 1
Test 1
Fiber cement (paper towels
AGM
#15 Felt Paper Fiber cement (paper towels
574
583
1005
984
75%
69%
For AGM-1 and Felt-1, water was poured between the OSB and drainage plane (ie. The AGM
or building paper) to simulate a leak or poor flashing. Walls were clad with vinyl siding as per
93
standard installation practice. Based on airflow testing, Straube and Smegal (2005) found that
the AGM system exhibited an equivalent cavity of 3mm. Drainage tests were conducted with
vinyl siding and fiber cement sheet cladding. In both cases the AGM drained as quickly and
retained slightly less water than walls with #15 felt. Walls constructed with the AGM also dried
more quickly under the influence of simulated wind and sun than similar walls with #15 felt.
AGM-1, tests 1 and 2 compared the drying performance of AGM, over untreated OSB and
clad with vinyl siding. The difference between tests 1 and 2 was the drying mechanism. AGM-1
test 1 used a 1 Pa wind pressure difference, and AGM-1 test 2 used simulated solar energy. As
expected, because of the relatively large size of the gap, drying due to ventilation was very
efficient (see Figure 9-12). The test walls equilibrated at approximately 100 g because the water
poured between the OSB and the AGM caused the moisture content of the OSB to increase to a
new equilibrium moisture content. AGM-1 test 2 took considerably longer to reach equilibrium
because it was dried by diffusion and simulated solar energy with no forced ventilation.
350
300
Mass of Water (g)
AGM-1 Test 1
AGM-1 Test 2
250
200
150
100
50
0
0
24
48
72
Time (hours)
Figure 9-12 : Results for AGM-1 Drying Tests
94
96
120
Felt 1, test 1 and 2 compared the performance of vinyl siding over #15 felt instead of AGM.
The water was again poured between the sheathing membrane and the OSB but because of
shingle style installation, the majority of the water drained to the front of the building paper after
the first piece, and consequently drained out the front of the vinyl siding. Felt-1 tests stored
slightly more water than AGM-1 tests, in part because of the greater storage capacity of the #15
felt, than the AGM.
350
300
Felt-1 Test 1
Felt-1 Test 2
Mass of Water (g)
250
200
150
100
50
0
0
20
40
60
80
100
120
Time (hours)
Figure 9-13 : Results of Felt Drying Tests (Felt 3 and 4)
The differences in drying rate for Felt-1 tests was not great because there was no intentional
gap for airflow even in the ventilated test. Felt-1 test 1 did start to dry initially quicker because
of ventilation, but Felt-2 drying reached a similar condition after one cycle of the solar lamps,
and eventually dried to a lower mass of water after five days. One reason for the slower drying
in this test method is because the water was trapped between the #15 felt and OSB in the upper
portion of the test wall with only diffusion and capillarity to move moisture out of the wall
95
system. Obviously, the air gap formed by the dimple sheet pattern in AGM 1 and 2 helped dry
the wall considerably faster.
9.2.6
Flow visualization
To help understand the different drainage patterns caused by physical characteristics in small
cavities, some flow visualization was conducted using a fiber cement sheet and lexan wall
system. The lexan was attached to the fiber cement with a 4mm gap formed by spacers at both
sides. The wall system was a scale model of a large wall system measuring 16” in height, with a
width of 11”. Flow visualization tests were conducted with two different cement fibreboard
sheets, similar to the previous section. One cladding sheet was designed to be more absorptive,
and one was designed to be less absorptive. The flow visualization helps explain how drainage
is affected by the physical characteristics such as absorptivity.
Point source water and
distributed water tests were conducted on the small scale wall system. Figure 9-14 shows the
drainage test results of the point source loading.
The more absorptive panel is on the left. As the board is wetted, the pattern becomes wider,
wetting more of the surface area. At the bottom of the drainage gap, there is considerably more
spreading, and a higher volume of water (darker dying) stored by capillarity between the
surfaces.
96
Figure 9-14 : Comparison of Flow Pattern for Point Source Load
For the distributed load test, a volume of water was poured into the gap continuously as the
container was moved back and forth across the wall system twice. The less absorptive panel is
on the left in Figure 9-15 and similar to the point source loading, the drainage paths are all very
narrow and well defined. On the absorptive sample, the drainage was much more evenly
distributed and constant across the width. The absorptive sample, also allowed moisture to get
under the spacers along the sides in places that were pressed very tightly between the faces. The
moisture was drawn underneath the spaces by the capillary forces of the cladding. Again, more
water was stored at the bottom of the drainage cavity of the more absorptive cladding than the
non absorptive cladding made obvious by the darker staining.
97
Figure 9-15 : Comparison of Flow Pattern for a Distributed Load
9.3
Drainage and Drying Results – Discontinuous Drainage Gaps
Another set of tests were designed to gain a better understanding of drainage and drying of
siding systems. The four siding systems tested were vinyl siding, fiber cement siding, cedar
siding, and Lousiana Pacific Smartside. These siding products were only characterized as to
their ability to drain and store water. There are many other aspects of related to siding durability
and overall quality that should be considered before deciding on which siding to use. Drainage
and drying tests were done to characterize and rate each siding products performance with
respect to drainage and drying. All of the siding drainage tests were conducted on a 3’x7’ frame
with a 3’x6’ test area. The sides of the test panel for all but the vinyl used fiber cement trim that
was treated to be nonabsorptive, and the trim was sealed to the weather resistant barrier, so that
water could not get underneath.
98
9.3.1
Vinyl Siding
The vinyl siding walls were constructed as per normal construction practice. The j-trim was
installed along both sides six feet in length. The j-trim was sealed to the sides of the wall panel
with aluminum tape so that water was unable to exit the sides of the wall under the j-trim. The
vinyl siding was installed loosely, as this is how it is installed in practice to allow for
contraction/expansion.
This may allow more water to get behind the siding, since it will not be
pressed tightly against the sheathing membrane. Vertical joints were installed in the vinyl to
more closely simulate realistic performance. Vinyl siding was tested on both Tyvek and #15 felt
building paper. A photograph of the vinyl wall testing is shown in Figure 9-16.
Figure 9-16 : Vinyl Siding Wall Test
99
During drainage, water exited the drainage holes in the bottom of the vinyl siding, joints in the
siding between horizontal pieces, and also out the j-trim as water was directed along the
individual pieces of siding. Previously, some undocumented testing was conducted, with vinyl
siding installed on plexiglas surface, eight feet wide, and six feet tall. During this testing water
poured into the top could be seen running along the channel in the siding to either side, and out
the j-trim. No water was observed exiting the bottom behind the vinyl as it all came out through
the drainage holes or through the j-trim. This finding was duplicated in this research as well as
in the field studies presented earlier by Straube et al. (2000).
During the disassembly of the cladding, two weeks after pouring water into the wall, water
was found trapped in the horizontal joints between siding pieces in the top four rows. After row
four, there was no evidence of wetting in the horizontal siding channels.
Following numerous drainage and drying tests of the vinyl siding, it was noted that as the wall
was removed from the test apparatus there was sufficient water still stored in the siding elements,
that free water ran out of the horizontal channels to the j-trim and onto the floor. There was an
estimated 25 mL of liquid water in the horizontal channels even after a week of drying.
Table 9-8 : Drainage Testing Results of Vinyl Siding Wall System
Wall
Test Number
Drainage Plane
Cladding
Initial Storage
(g/m2)
Final Storage
(g/m2)
Percentage
Increase
Vinyl-1
Vinyl-1
Vinyl-1
Test 4
Test 2
Test 5
Tyvek
Tyvek
Tyvek
Vinyl siding
Vinyl siding
Vinyl siding
74
78
81
92
93
100
25%
20%
24%
Vinyl-2
Vinyl-2
Vinyl-2
Test 11
Test 9
Test 7
#15 Felt Paper
#15 Felt Paper
#15 Felt Paper
Vinyl siding
Vinyl siding
Vinyl siding
88
93
91
103
109
113
17%
17%
24%
The storage amounts in all the vinyl siding tests are very repeatable. Figure 9-17 shows the
repeatability in drainage tests on Tyvek. The walls with #15 felt are consistently higher storage
amounts but not significantly higher. The drainage plane plays only a small role in the storage
values because the majority of the area of the drainage plane was not wetted.
100
The percentage increases are a little greater then negligible but are among the smallest changes
in any wall system tested. Since the material surfaces are largely nonabsorbent, it is assumed
that very little excess water will be stored in subsequent wettings.
400
350
Test 2
Test 4
Test 5
Mass of Water (g)
300
250
200
150
100
50
0
0
5
10
15
20
25
30
35
Time (min)
Figure 9-17 : Drainage Test Results for Vinyl Siding on Tyvek
The drying curves for the siding tests were very similar in shape for the Vinyl-1 tests and
Vinyl-2 tests. For the vinyl siding test, drying was done by wind, sun, and naturally. After five
days of drying, the mass of water in the Vinyl-1 (Tyvek) tests were lower than similar drying
methods in the Vinyl-2 (#15 felt) tests. This is likely because of the absorbed moisture in the
#15 felt compared to the nonabsorptivity of the Tyvek. Figure 9-18 shows the drying curves for
the Vinyl-1 tests (with Tyvek), and Figure 9-19 shows the drying curves for the Vinyl-2 tests
(with #15 felt).
101
180
160
Mass of Water (g)
140
120
100
80
60
40
20
0
-20
0
24
48
72
96
Test 5 - fan
Lights On
120
Time (hours)
Test 4 - unaided
Test 2 - heat
Lights Off
Figure 9-18 : Drying Curves for Vinyl Siding over Tyvek Using Different Drying Techniques
200
180
Mass of Water (g)
160
140
120
100
80
60
40
20
0
0
24
48
72
96
120
Time (hours)
Test 7 - fan
Test 9 - heat
Test 5 -unaided
Lights On
Lights Off
Figure 9-19 : Drying Curves for Vinyl over #15 felt Using Different Drying Techniques
102
Vinyl-1 walls dried exactly as anticipated. The intial drying was fastest by ventilation drying,
and slower by solar heating and natural drying. Vinyl-1 Test 4 dried the least after five days, and
Vinyl-1 test 2 dried the most due to the amount of added energy. In Vinyl-2 walls with #15 felt,
the results were unexpected for unknown reasons. The solar wall still dried the most after five
days, but the naturally drying wall dried more than the fan ventilated wall although not
significantly (<10g).
The drying results for Vinyl-1 and Vinyl-2 show similarities to the AGM-1 and Felt-1 drying
tests where the nonabsorptive drainage materials of Vinyl-1 and AGM-1 behaved more
predictably during drying than Vinyl-2 and Felt-2 with the absorptive #15 felt. These differences
could be caused by stored drainage water, but also may be more sensitive to small changes in the
laboratory RH.
9.3.2
Fiber Cement Plank
The fiber cement plank was installed as per the installation instructions included in the
appendix. The plank has been back primed but inspection of the plank shows different amounts
of priming on each plank indicated by different colours on the back side.
The butt joints were backflashed with Tyvek as per the instructions and all the cut edges were
sealed with primer. Tests were done with Tyvek and #15 felt paper as drainage planes. The
different combinations are shown in Table 9-9.
Table 9-9 : Test Matrix for Fiber Cement Testing
Wall
FCSiding-1
FCSiding-1
FCSiding-1
Test Number
Test 10
Test 8
Test 6
Drainage Plane
Tyvek
Tyvek
Tyvek
Cladding
Back primed fiber cement
Back primed fiber cement
Back primed fiber cement
Initial Storage
(g/m2)
63
64
62
Final Storage
(g/m2)
87
85
91
Percentage
Increase
39%
32%
47%
FCSiding-2
FCSiding-2
Test 16
Test 14
#15 Felt Paper
#15 Felt Paper
Back primed fiber cement
Back primed fiber cement
67
60
93
95
40%
57%
Water was poured in behind the first plank and started coming out between the first two
planks.
It was unclear during the original testing, how much water was getting behind
103
subsequent planks since it was difficult to differentiate between water running over the front of
the wall, and water coming between the planks.
The importance of making sure test materials are at equilibrium with lab conditions was made
obvious in the first test with fiber cement plank. It had been received from California via courier
less than a week before constructing the first test wall. The siding had been stored in the lab for
a week, but during the drying test (Figure 9-20), it became obvious that the materials were not at
equilibrium with the lab. After less than 40 hours of drying, the wall had dried to its starting
weight, and after 140 hours, the wall had dried a further 300g. An individual plank was dried
and weighed and it was found that there was a total of approximately 2kg of extra moisture
adsorbed into the cladding material on the test wall.
The drying curve for the cement fiber board is much different than the drying curves for the
vinyl siding testing. The preliminary drying curve that is quite steep for the vinyl siding as well
as the EIFS testing, is barely noticeable, and the secondary drying, typical of moisture
redistribution inside the wall materials, predominates.
104
200
100
Mass of Water (g)
0
-100
-200
-300
-400
0
20
40
60
80
100
120
140
160
Time (hours)
Figure 9-20 : Drying Test for Fiber Cement Board Not at Equilibrium with Laboratory
One complication with the fiber cement was that it gained a significant amount of weight after
two pours. This was more of an afterthought to most testing, so was not always checked. One
drainage test was conducted with the fiber cement and Tyvek wall to find the maximum storage
amount.
The data is shown below with the increases of weight every time water was added.
Large increases in added weight were also seen previously in the fiber cement sheet testing.
105
500
450
Mass of Water (g)
400
350
300
250
200
150
100
50
0
0
15
30
45
60
75
90
105
Time (min)
Figure 9-21 : Attempting to Reach Maximum Storage in Fiber Cement plank
Table 9-10 : Drainage Test Data for Fiber Cement Maximum Storage Test
Pour #
first
second
third
fourth
fifth
sixth
Water Stored
2
(g/m )
62
91
119
146
164
186
Percentage
Increase
47%
30%
23%
12%
14%
To better understand the drainage of the fiber cement plank wall, during FCSiding-1 test 10,
purple dye was added to the water to help determine water paths. It was still difficult during
drainage to differentiate between water flowing over the surface and water flowing between
planks, and there was considerable staining of the front surface (Figure 9-21). The dye was only
used on the fiber cement wall because of the abundance of test material, but it is assumed based
on similar geometry, that similar results would be found for both the cedar siding and the LP
Smartside.
106
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Figure 9-22 : Analysis of Drainage Patterns on Clapboard Siding
Most of the drained water was shed to the front of the siding after the first plank. There was
evidence of a small amount of water behind plank number two and even less behind plank
number three (Figure 9-23). There was also evidence in every plank that water had been wicked
by capillarity up from the bottom into the drainage gap. It is unknown how much water was
stored by capillarity but knowing that the outside surface is relatively nonabsorbent, and only
one plank was heavily wetted on the back, it would appear that capillarity caused a significant
107
amount of water to be stored. Also, on subsequent pours, the amount of capillary action was
likely the greatest increase in storage since the front surface was already completely wetted with
surface droplets, and it is unlikely even after subsequent wettings, that water got behind
subsequent planks. This could be a significant method of storage in any clapboard siding such as
fiber cement, LP Smartside, or cedar siding.
Figure 9-23 : Visual Inspection of the Back of Fiber Cement
For the drying in the fiber cement, the initial drying curve was much shorter than the vinyl
drying curve. This is because there is a much larger quantity of water absorbed into the material,
than held on the surface of nonabsorbent materials (Figure 9-24). Drying with the fan resulted in
slightly more drying, but not significantly.
108
160
140
Test 16 - no fan
Test 14 - fan
Mass of Water (g)
120
100
80
60
40
20
0
0
20
40
60
Time (hours)
80
100
120
Figure 9-24 : Drying Curves for Fiber Cement Cladding Walls With #15 Felt Paper
9.3.3
Louisiana Pacific Smartside
According to marketing, LP SmartSide products offer the natural look of cedar, plus the added
durability and weather resistance that comes with using a highly engineered wood product.
There have been issues and concerns in the past with subjecting an engineered wood such as
oriented strand board (OSB) to the elements. This testing did not deal with the long term
durability issues that may or may not exist with OSB siding, but only the drainage and drying
capability of the siding product. The test wall was constructed as per the installation instructions
from Louisiana Pacific. Instead of backflashing the butt joints between planks, similar to the
Hardiplank and cedar siding installation instructions, it was recommended to caulk the joints. It
has been found that sealants do not span cracks well, do not withstand movement, and will
degrade from sunlight, temperature, and oxidation (Lstiburek 2003) so this might be a longterm
durability issue, as well as an aesthetic issue.
109
In the two drainage tests conducted on Smartside it was found that it stored the least water of
any siding combination, but only slightly less than the fiber cement construction. This may have
been due to a slightly more impermeable treatment on the back of the Smartside which would
resist storage caused by capillarity between the planks. The difference between fiber cement and
Smartside with respect to drainage is insignificant.
Table 9-11 : Test Matrix for LP Smartside Testing
Wall
LP-1
LP-1
9.3.4
Test Number
Test 17
Test 15
Drainage Plane
Tyvek
Tyvek
Cladding
LP Smartside
LP Smartside
Initial Storage
(g/m2)
59
57
Final Storage
(g/m2)
82
75
Percentage
Increase
40%
31%
Cedar Siding
The cedar siding stored the most moisture of any siding product (Table 9-12). This is likely
because the cedar siding was tested untreated. It was tested untreated so storage values could be
determined for untreated cedar and future tests can be conducted for painted cedar siding. It is
known that painting or treating the front surface of the cedar siding will help it last longer, look
better, and resist moisture penetration. However, from the dye test, it is unclear how important
backpriming clapboard siding is because the water is immediately drained to the front. Speaking
with local house builders, cedar siding is generally installed without backpriming and then
painted after installation.
The percentage increases between water applications were quite large which was expected
because of the lack of surface treatment. Painting or treating the front of the siding will greatly
reduce the amount stored in the first and subsequent wettings. Given the capillary suction
between siding pieces and subsequent storage noted in testing, it may be beneficial to paint the
siding before installation so that the overlapping area can also be treated. It is unknown how
significant capillary storage is and whether prepainting the siding before installation provides
significant benefits. Testing of painted and primed cedar is recommended.
110
Table 9-12 : Test Matrix for Cedar Siding Testing
Wall
Cedar-1
Cedar-1
Test Number
Test 13
Test 12
Drainage Plane
Tyvek
Tyvek
Cladding
Cedar Siding Untreated
Cedar Siding Untreated
Initial Storage
(g/m2)
137
129
Final Storage
(g/m2)
222
224
Percentage
Increase
62%
73%
The drying curve for the cedar siding started as expected with the fan drying the wall quicker
than natural drying, but at approximately the thirty hour mark, the unaided drying passed the fan
drying, and was dryer after 120 hours. As usual with the absorbent cladding, the outcome did
not perform quite as expected. Because of a drop in RH of almost 10% shown in Figure 9-25
during Test 13, the drying curve for Test 13 fell below Test 12, which may or may not have
occurred otherwise.
400
60
Test 12 - Fan
Test 13 - no fan
RH Test 13
50
Mass of water (g)
300
40
250
200
30
150
20
100
10
Relative Humidity Test 13 (%)
350
50
0
0
0
24
48
72
96
120
Time (hour)
Figure 9-25 : Drying Comparison of Cedar Siding Testing
The initial drying in the cedar was very fast, drying over half of the stored moisture in both
tests in under 12 hours which is surprising since there was a large amount of water absorbed into
the materials and not held on the surface in tension.
111
From the drying results of the absorbent
fiber cement, it was thought the drying might have a shorter or more gradual preliminary drying
curve. The water must not be held in the cedar siding as tightly as fiber cement.
9.4
Analysis of Results
It was found that the test method and results for drainage were very repeatable between
numerous tests of the same wall. The method also generated repeatable results on similarly
constructed walls in Fontana, California on a different experimental apparatus. One drying test
was conducted to test repeatability using identical drying conditions, and the results were nearly
identical.
All of the test walls drained the testing water quickly with the exception of Stucco-1. This is
thought to be a problem with the test wall construction and was rectified.
Six different EIFS walls were tested for drainage and drying. It was shown that the trowel
applied water proof barrier may have absorbed a significant amount of water in EIFS walls 2, 4
and 6. EIFS-3 had the highest storage of any EIFS wall because of the increased surface area in
the drainage space caused by the grooved EPS and granular vent assembly. None of the EIFS
walls tested met the CCMC standards of less than 30 g/m2 retained water.
All of the drying curves show an initial drying section lasting up to two days during which it is
assumed liquid water droplets are evaporated from the surfaces of nonabsorptive materials. The
initial drying always has a much higher rate of drying. The secondary drying is slower and is
dependant on moisture distribution inside the materials. Walls with low permeance claddings
and small ventilation gaps have the slowest drying.
It was shown that drying with the fan increased the initial drying rate in nearly every case. This
was more evident in walls with a larger drainage cavity such as Stucco-2 and AGM-1 when
compared to similar walls with a smaller drainage cavity such as Stucco-1 and Felt-1.
New Zealand style walls use blocking between studs rather than structural sheathing. It was
shown that the blocking causes nonuniform moisture distribution and head pressures that may
cause failure to resist water penetration for some housewraps.
112
The Air Gap Membrane (AGM) was tested with both vinyl siding and fiber cement sheet, and
compared to similar tests with building paper. Both times, the AGM drained as quickly, retained
slightly less water, and dried more quickly that building paper.
Flow visualization was conducted on two different mixtures of fiber cement sheet. The more
absorbent sheet, had a considerably wider distribution across the width in both the point source
and distributed load. The water was able to get under the edges of the wall that were squeezed
tightly together by moving through the sheet. The less absorptive sheet produced much more
defined and thinner flow patterns in both the point source load and distributed load.
For the siding testing, water drained over the front of the wall, and very little was known about
the drainage gap. Dye was used to determine the paths of water, and it was found using the fiber
cement siding, that almost all the water exited the wall after the very first plank, and there was no
evidence of water in the gap by the fourth plank. This was assumed to be the same based on
similar installation and geometry for both the LP Smartside and the cedar siding. This meant
that water was stored on the front of the planks, and there was evidence of moisture being
wicked back up into the joints between planks from the bottom.
Since the cedar siding was untreated, it stored the highest amount of water. The exterior
surfaces of the Smartside and fiber cement arrived from the factory pretreated. The vinyl siding
stored the second highest amount of water because of all the grooves and channels in the design.
Vinyl siding is incapable of absorption so all the water was stored as liquid. The least amount of
storage occurred in the fiber cement and the Smartside, because the water was mostly on the
front of the siding. It was shown however with the fiber cement that subsequent wettings kept
increasing the amount of storage. This was not checked on the Smartside, but would probably
have similar results.
The quickest initial drying was expected to be in the vinyl siding, since no water is actually
absorbed, but it was actually in the cedar siding. This may have been due to the relatively high
amount of water that was stored in the cedar siding. The shortest initial drying rate was in the
fiber cement plank. This is because of the physical characteristics of the fiber cement, since
similar amounts of water on other sidings dried faster.
113
10.0
Conclusions
From an analysis of a previous driving rain study of Canadian cities it was found that the
intensity of an average driving rain event was 0.7 mm/hr (0.012 L/m2-min). The 1% rain event
(a level exceeded 1% of the driving rain hours) was chosen as the extreme rain event as no
precedent could be found. For the 40 cities investigated, the 1% driving rain event intensity was
found to range from a low of 3.0 mm/hr (0.05 L/m2-min) to a high of 10.2 mm/hr (0.17 L/m2min).
The Moisture in Exterior Walls (MEWS) water ingress study conducted by the Institute for
Research in Construction (IRC) employed water application rates (1.7 L/m2-min and more) and
air pressure differences (100 Pa to 500 Pa) orders of magnitude higher than those calculated for
extreme rain events.
These large application rates were reportedly necessary to achieve
measurable amounts of leakage. The MEWS research did show that gravity alone can cause a
significant amount of leakage.
Based on the range of cladding leakage rates found in the MEWS study and the range of
driving rain intensities that can be experienced, it can be concluded that the rate of water
penetration of the cladding can vary by several orders of magnitude.
However, even small gaps
allow drainage rates that are significantly higher than the highest predicted leak rates. For
example, a 0.5 mm gap was calculated to drain at a rate of 1530 mL/min per meter of wall width
when the highest leakage rate calculated was 560 mL/min per meter of wall width.
A test method and apparatus were developed to investigate the drainage, storage, and drying
characteristics of a range of typical North American framed wall systems. This method and
apparatus were able to generate repeatable results in the lab under the same conditions. They also
generated repeatable results on similar walls when tested at another facility with a different
apparatus.
Test walls included samples with cladding of stucco, EIFS, fiber cement sheet, fiber cement
plank siding, vinyl siding, cedar plank siding, and prefinished OSB siding. Both testing and
114
analysis found that even a small gap (less than 1 mm) will drain water at a rate considerably
greater than it is expected to penetrate most walls. For example, the measured drainage rate of a
gap of about 1.0 mm wide was found to be in excess of 1.5 litre/minute-meter width. Walls with
lap siding tended to drain water out onto the face of the plank immediately below the plank at
which the water was injected.
In all of the full-scale wall drainage tests some of the water was stored and did not drain.
During testing of non absorptive materials (with no cladding), a suspended polyethylene sheet
consistently stored 35 g/m2 and a single sheet of plexiglas stored 65 g/m2. Drainage tests of a
plexiglas wall with a 1 mm gap resulted in storage amounts of approximately 24 g/m2. The
reason for the reduced storage in the small gap versus the exposed material was not determined.
Six different EIFS walls were tested for drainage and drying. It was shown that the trowelapplied water resistant barrier may have absorbed a significant amount of water in three of the
EIFS test walls. An EIFS test wall with a grooved EPS drainage gap and granular vent assembly
exhibited the highest storage because of the increased surface area in the drainage space. None
of the EIFS walls tested met the proposed CCMC standard of less than 30 g/m2 retained water
after drainage.
A wall that used an Air Gap Membrane (AGM) was tested with vinyl siding and fiber cement
sheet cladding and compared to similar tests with #15 felt. In both cases, the AGM drained as
quickly, retained slightly less water, and dried more quickly than the wall with #15 felt.
The cedar siding in the cedar plank test wall was untreated. Hence, it absorbed and stored the
greatest amount of water of all the siding products tested. Surprisingly, the wall with vinyl
siding stored the second highest amount of water because of liquid water retention in the grooves
and channels provided by the siding. The least amount of storage occurred in the fiber cement
and the prefinished OSB siding (Smartside), because the water was mostly on the front of the
siding and the exterior surfaces of the Smartside and fiber cement arrived from the factory
pretreated.
All of the drying curves show an initial drying stage lasting up to two days during which it is
assumed liquid water droplets were evaporated from the surfaces of non-absorptive materials.
115
This initial drying always has a higher rate of drying than the second stage. The secondary
drying stage is slower and is dependant on the rate of moisture distribution and storage in the
materials lining the drainage space (i.e., the drainage plane and the cladding). Walls with low
vapor permeance claddings and small ventilation gaps exhibited the slowest drying.
It was shown that drying with a small simulated wind pressure (provided by a fan) increased
the initial drying rate in nearly every case. In the hygroscopic claddings the fan did not always
accelerate drying. This was more evident in walls with a larger ventilation cavity (such as
strapped stucco and AGM wall) than similar walls with a smaller ventilation cavity (such as
stucco directed applied to paper and vinyl on felt). Ventilation drying was shown to be effective
even in small gaps (1mm). Ventilation drying is expected to increase as the gap width increases
but it is unclear above which gap width no improvements in drying are achieved.
The fastest initial drying was expected to be in the vinyl siding over Tyvek, since no water can
be absorbed by any of the materials. However, the fastest drying was actually observed in the
wall with cedar siding. This is likely due to the relatively high amount of water that was stored
in the cedar siding. The slowest initial drying rate was observed in the wall clad with fiber
cement plank. This is because of the physical characteristics (low moisture diffusivity) of the
fiber cement, since similar amounts of water on other sidings dried faster.
To build on knowledge gained in this thesis more investigation is needed to analyze the role of
surface contact angles and moisture stored on non absorptive surfaces. This recommendation is
based in part on the surprisingly high storage amount on the surface of the plexiglas compared to
the polyethylene sheet. Although it was shown that ventilation is important for drying in air
spaces, even small air spaces, a more detailed study of ventilation drying should be conducted to
determine the optimum gap width for ventilation drying.
Non-absorptive enclosure materials behaved much more predictably during storage and drying
than similar walls with absorptive (hygroscopic) materials. Further analysis may reveal methods
to more accurately predict the performance of absorptive wall system materials. Other future
work that may be useful in predicting wall performance is the correlation of hygrothermal
modeling with the storage and drying results.
116
Finally, it was shown that some test standards and performance design criteria currently being
used for testing impose very unrealistic loads and set unrealistic performance thresholds. These
test standards and performance specifications should be re-visited to more realistically reflect
actual loadings and performance. Other test standards are in the process of being developed (eg.
ASHRAE 160P) to help in wall design using a percentage of wind driven rain as leakage
amounts.
117
11.0 References
Allen, E., How Buildings Work, 3rd Ed. Oxford Press 2005.
Blocken, B., Wind-driven Rain on Buildings: Measurements, Numerical Modeling and
Applications, Ph.D. thesis, Laboratory of Building Physics, Department of Civil Engineering,
Katholieke Universiteit Leuven, 2004.
Blocken, B., Carmeliet, J., “A Simplified Approach for Quantifying Driving Rain on Buildings.
Buildings IX, ASHRAE 2004.
Blocken, B., Carmeliet, J., “A review of wind-driven rain research in building science”,
Journal of Wind Engineering and Industrial Aerodynamics 92(13): 1079-1130. Elsevier 2004b.
CCMC Technical Guide for External Insulation and Finish Systems, Masterformat No. 07240,
Appendix A4 “Exterior Insulation and Finish Systems (EIFS), Class PB on Wood Substrates”,
January 2004.
Choi, E.C. Numerical Simulation of Wind-Driven Rain Falling onto a 2-D Building. Asia Pacific
Conference on Computational Mechanics, Hong Kong, pp. 1721-1728, 1991
City of Vancouver Building By-law, 1999 IRC/NRCC
CMHC, Survey of Building Envelope Failures in the Coastal Climate of BC. Report by
Morrison–Hershfield for CMHC, Ottawa, Nov. 1997
Garden, G.K., Rain Penetration and Its Control. Canadian Building Digest 40, Division of
Building Research, National Research Council of Canada, Ottawa, 1963.
Gatley, D.P., “Psychrometric Chart Celebrates 100th Anniversary”, ASHRAE Journal November
2004, pp 16-20.
Handegord, G., Hutcheon, N. Building Science for a Cold Climate, Canadian Institute for
Research in Construction, Ottawa 1995
Hazleden, D.G., Morris, P.I., “Designing for Durable Wood Construction: the 4 Ds”, Eighth
International Conference on Durability of Building Materials and Components, Vancouver,
Canada, 1999, pp 734-745.
Herbert M.R., Open-Jointed Rain Screen Claddings. Building Research Establishment Current
Paper 89/74, HMSO Garston, U.K., 1974.
118
Hoppestad, S. Slagregn i Norge (in Norwegian). Norwegian Building Research Institute, rapport
Nr. 13, Oslo, 1955
Hutcheon, N.B., Requirements for Exterior Walls. Canadian Building Digest 48. Division of
Building Research, National Research Council, Ottawa, 1963.
Hutcheon, N.B., Principles Applied to an Insulated Masonry Wall. Canadian Building Digest 50,
Division of Building Research, National Research Council, 1964.
Johansson, C.H., “The Influence of Moisture on the Heat Conductance of Bricks.”
Byggmastaren, Nr. 7, 1946, pp. 117-124
Karagiozis, A.N., “Development of Wall Assembly System Properties Used to Model
Performance of Various Wall Claddings”, Buildings IX Proceedings. ASHRAE 2004.
Kerr, D., Keeping Walls Dry. Continuing Education Articles for Architects, CHMC. November
2004
Lstiburek, J., “Water-Managed Wall Systems”, JLC, March 2003
Knowles, R., Energy and Form. MIT Press, Cambridge, Massachusetts, 1974.
Kumaran, Marinkal, et al., “Fundamentals of Transport and Storage of Moisture in Building
Materials and Components”, Moisture Control in Buildings, ASTM Manual Series 18, chapter 1,
editor H.R. Trechsel, 1994.
Lacasse, M.A. et al., Report from Task 6 of MEWS Project : Experimental Assessment of Water
Penetration and Entry into Wood-Frame Wall Specimens - Final Report, Institute for Research
in Construction, Feb. 2003
Lacasse, M.A., Recent Studies on the Control of Rain Penetration in Exterior Wood-Frame
Walls, Institute for Research in Construction, 2003
Makepeace, C. B., “Wrap it up: building houses with the skin on the outside”, Home Energy,
November/December, pp. 13-17, 1999.
Middleton, W.K. “Invention of the meteorological instruments”. The John Hopkins Press,
Baltimore, Maryland, 1969
Ritchie, T. Rain Penetration of Walls of Unit Masonry. Canadian Building Digest 6, National
Research Council of Canada, Ottawa, 1960.
Ritchie, T. Cavity Walls. Canadian Building Digest 21, National Research Council of Canada,
Ottawa, 1961.
119
Schumacher, C. et al., Ventilation Drying in Wall Systems, International Building Physics
Conference, Belgium. 2003.
Sereda, P.J., Feldman, R.F., Wetting and Drying of Porous Materials. Canadian Building Digest
130, National Research Council of Canada, Ottawa, 1970
Straube, J., The Performance of Wall Systems Screened With Brick Veneer, MASc dissertation,
University of Waterloo, 1993.
Straube, J. et al., Drainage Behind Stucco and Vinyl Cladding, 2000.
Straube, J. et al., “Field Studies of Ventilation Drying”, ASHRAE 2004.
Straube J., and Burnett E., Building Science for Building Enclosures, Building Science Press,
Westford, Massachusetts, 2005.
Van Straaten, R., Measurement of Ventilation and Drying of Vinyl Siding and Brick Clad Wall
Assemblies, MASc dissertation, University of Waterloo, 2003.
120
Appendix A
Airflow Testing
121
Air Flow Tests
Intent
The air flow testing procedure was designed to determine the amount of airflow under a
range of relatively low air pressure differences. Pressures over the height of a wall tend to be
in the range of 1 to 10Pa most of the time under natural exposure conditions.
Set up
The test wall was opened if required and all joints and seams in the drainage gap were sealed.
The exact procedure for sealing the panels different because of different wall construction. In
som cases, Peel-and-stick was placed along the entire length of the panel covering all the
seams along the sides as seen in Figure 1. Next, a four foot length of PVC pipe with a t-joint
in the middle was cut in half lengthwise and sealed against the top edge of the wall panel as
shown in Figure 2.
Test EIFS Assembly
Silicone sealant
Edge details as in practice, flush with studs
Peel and Stick covers vertical edges
Figure 1: Sealing Wall Section with Silicone and Peel and Stick
The air test was conducted using a calibrated air flow device that controls the amount of air
being passed through the wall section. Negative pressures were applied to the test walls
since negative pressure tends to pull all the seals tighter to the wall section rather than
opening them up. This tends to result in slightly lower system leakages than with positive
pressure, but these differences are expected to be insignificant for a full-scale wall in service.
A schematic of the test apparatus can be seen in Figure 3. The first air test was conducted
while leaving the opposite end of the wall section open thereby allowing the maximum
amount of air to flow through the drainage gap. A digital manometer was connected to the
122
PVC pipe at the top edge of the wall to measure the pressure difference across the wall
section. All of the equipment used for testing is shown in a photo in Figure 4.
Figure 2: Schematic of Air Testing Manifold
Pressure Transducer
Rotometer
Fan
Control Valve
Figure 3: Schematic of Test Apparatus
123
Figure 4: Air flow test setup
The wall was also air tested with the bottom of the drainage gap sealed to determine the
quantity of all airflow paths other that the intended one. This approach accounts for small
leaks (in the wall or the apparatus) that may not be perfectly sealed. This quantity is termed
system leakage. The results from both tests are plotted and a power law equation is derived
to best fit each set of data points. The equation for the sealed wall can then subtracted from
the equation for the open wall, and the resulting line can be plotted.
For ventilation flow through an enclosed cavity, it can be assumed that the flow will be
laminar. Using a simplified Darcy-Weisbach equation for laminar flow, different gap sizes
and air flows were used to calculate corresponding pressure differences across the wall. Lines
were plotted showing gap sizes for the corresponding pressure and flow rates. The flow and
pressure relationships that were found for the experimental walls are plotted along with the
theoretical gap sizes for comparison.
124
EIFS 6 Wall Airflow versus Ideal Gap Widths 3' x 6' Cladding Area
Cavity Depth (mm)
40 mm
100
30 mm
25 mm
20 mm
15 mm
10 mm
9 mm
8 mm
7 mm
6 mm
5 mm
Air Flow (L/s)
4 mm
10
3 mm
2 mm
1
1 mm
0.1
0.1
1
10
100
Pressure (Pa)
Comparison of the Different Wall Sections
to Ideal Cavity Flow (4ft)
Cavity Depth (mm)
40 mm
100
30 mm
25 mm
20 mm
10 mm 9 mm 8 mm
15 mm
7 mm
6 mm
5 mm
4 mm
Air Flow (L/s)
3 mm
10
2 mm
1
1 mm
0.1
0.1
1
10
100
Pressure (Pa)
Stucco - 19mm Strapping
Stucco - Direct Applied
125
Air Gap Membrane
Comparison of the Different Wall Sections
to Ideal Cavity Flow
Cavity Depth (mm)
40 mm
100
30 mm
25 mm
20 mm
15 mm
10 mm
9 mm
8 mm
7 mm
6 mm
5 mm
Air Flow (L/s)
4 mm
10
3 mm
2 mm
1
1 mm
0.1
0.1
1
10
100
Pressure (Pa)
Stucco 2
EIFS 4
EIFS 1
126
EIFS 2
Stucco 1
EIFS 3
Appendix B
Wall Construction Specifications
127
128
129
130
131
132
133
134
http://www.cedar-siding.org/installing_siding/bevel-siding.htm
135