insulated pitched roofing

DOW CONSTRUCTION PRODUCTS
(a division of the Dow Chemical Company Ltd)
“INSULATED PITCHED ROOFING”
Welcome to this RIBA approved CPD self tutorial.
First some information about the Dow Chemical Company itself:
US origin, 100 years old.
2nd largest chemical company in the world
Produces: chemicals, plastics, agrochemicals.
Annual sales: £18 billion.
Employs: 45,000 globally (Europe 8,000)
Dow in the UK
STYROFOAM* production since 1969 : polystyrene produced at Barry,
Wales; extruded foam insulation produced in Kings Lynn.
Dow Construction Products offers the STYROFOAM range of blue
extruded polystyrene foam insulation:
Floors
- Floormate* 200,350,500 and 700
Cavity Walls
- Wallmate* CW
Walls internally
- Styrofoam* IB
Structures below ground
- Perimate* DI
Pitched Roofs
- Roofmate* PR, RL
Inverted Flat Roofs
- Roofmate* SL, LG
Conventional Flat Roofs
- Deckmate* CM, FF
* Trademarks of the Dow Chemical Company
Dow Construction Products
Insulated Pitched Roofing
This self-tutorial seminar covers all aspects of the so called “ Warm
Roof Concept” at rafter level pitched roof insulation.
You will discover
• The insulation options
• The advantages of the “warm” versus the “cold” roof
• How a “warm” roof is constructed
• The general design considerations, relevant codes of
practice and applicable standards to adhere to
• The role and selection of the various components with
particular emphasis on the insulation, the underlay,
fasteners and methods of securement
• The relevance and importance of the building physics
issues, thermal insulation, condensation and ventilation
• The “ins and outs” of detail design: eaves, ridge, valley,
hip and roof penetrations
• How the warm roof concept has been put to the test in
the field
INSULATED PITCHED ROOFING
INTRODUCTION:
It is estimated that today around 10% of new pitched
roofs are insulated at rafter level and that this
figure is increasing.
Various insulation solutions are available which are
dependent on the type of insulation used and its
location ( ie above, between or below the rafters or a
combination of these ), and the type of underlay
used. Although the insulation of pitched roofs cannot
be considered a new application it is now the subject
of much debate both in the technical press and within
the industry itself - indeed the BRE, NFRC and BSI
are all actively involved.
The aim of this seminar is to review the application
from an insulant manufacturer’s point of view.
CONTENT
•
Insulation options
•
Advantages of an insulated
roof structure
•
The Warm roof concept
•
Design considerations
•
Roof build-up: the components
•
Building Regulations: requirements
•
Case study
•
Detailing
•
Conclusions
Roof structure: uninsulated
attic/loft
space
insulation at
ceiling level
• insulation at ceiling / joist level - mineral / glass
fibre normally used
• attic / loft space ventilated (vents provided at eaves
and at ridge)
Note: Could adequate ventilation be provided by a
water vapour permeable (breather) underlay and
thus do away with providing vents at eaves’ and
ridge level ?
Roof structure: insulated
insulation at
rafter level
room in
the roof
• Insulation
can be a) above,
b) between
c) below the rafters
or a combination of these
• ‘Warm’ roof
insulation above rafters
sometimes referred to as sarking insulation
(see BRE Thermal insulation: avoiding risks BR262
• Hybrid roof : insulation between and/or under rafters.
Note: Focus of this seminar will be on the ‘warm’ pitched roof as this is the
optimum ( and perhaps the most challenging ) of the insulation options.
ADVANTAGES : INSULATED VS
UNINSULATED ROOF STRUCTURE
• Increased living /working space for same
“footprint”
• Additional space at lower cost
• Added value
• Allows room to grow
Cost of providing additional space in the attic can be less than
50% of the standard floor cost.
plus ----with a ‘warm’ roof:
- reduced risk of condensation on structural membranes.
- thermal movement of roof structure reduced.
- roof structure kept dry - no need for timber
preservative treatment.
THE WARM PITCHED ROOF
- roof build up
Counterbatten
Vapour permeable
underlay
Tiling batten
Insulation
Tiles
Rafter
• Insulation shown above and between rafters
• Vapour permeable underlay (breather type) can be laid either in direct
contact with the insulation ( as shown ) or over the counterbattens
• Suitable for new build or where the roof covering is to be replaced (
note increase in roof height ! ) and where it would be difficult to provide
eaves ventilation
Note: Need for a vapour control layer (VCL) ? YES for areas exposed to
high humidity levels e.g swimming pools, kitchens, changing
rooms.
Use plasterboard (13 mm) to cover exposed XPS insulation.
THE WARM PITCHED ROOF CONCEPT
• rigid insulation over (and between) rafters
plus
• a water vapour permeable (breather) underlay
Note: Where proprietary products are to be specified,
manufacturers’ recommendations should be followed.
Designers should satisfy themselves that the performance of
these products and the given recommendations have been
proven by relevant experience in use or by test data based
on the conditions and methods of application in equivalent
and appropriate internal and external climatic conditions.
THE WARM PITCHED ROOF
• First …… thatched roofing !
• Developed from Scottish sarking - early 80’s
• Agrément certification - mid 80’s
• Thousands roofs, millions sq metres installed
• Includes all insulation types
• Minimal condensation problems
• No securement problems
Note:
Thatched roof - really is a “breathing” warm roof
Sarking
- originated in Germany / Scandinavia refers to a sheet or
underskirt of boarding.
- traditionally in Scotland 25mm thick close timber boarding at
underslating level.
- helps reduce effect of wind uplift on slates.
Design considerations
! BS 5268 : Part 7 : 1990 Roof
construction - rafters & purlins
(Approved Document A : 1994 )
! BS 5534 : Part 1 : 1997 Slating & tiling
! BS 6399 : Part 1 : 1984 Dead loading
! BS 6399 : Part 2 : 1995 Wind loading
! BS 6399 : Part 3 : 1988 Imposed &
snow loading
ROOF BUILD-UP - THE COMPONENTS
Rafters
Vapour Control Layer
Insulation
Underlay
Battens
Fasteners
RAFTERS
Consider:
•
Roof slope
•
Cut vs trussed
•
Dimensions (and tolerances)
•
Spacing
•
Bracing
Note:
Must assume that insulation does not contribute to
the racking strength of roof structure.
VAPOUR CONTROL LAYER (VCL)
• Usually a membrane (eg 500 gauge polyethylene
sheet)
• Substantially reduces transfer of water vapour
• Installed on warm side of insulation
A VCL reduces water vapour transfer through any building component in
which it is incorporated.
(BRE document BR 262: ‘Thermal insulation - avoiding risks’ specifies a
minimum water vapour resistance of 200 MNs/g. BS 5250 refers to the use
of 500 gauge polyethylene with a range of 200 to 350 MNs/g, typically 250
MNs/g.)
The VCL should be installed on the warm side of the insulation. ( Note that a
VCL at ceiling level will require increased ventilation below it during the wet
trade phases of construction.)
Performance of a VCL also is dependant on workmanship and build ability see Clause 9.2 of BS 5250.
It is essential that it is adequately lapped and sealed so as to maintain its
integrity.
Particular care should be given to detail design and installation around
penetrations through the VCL (e.g services, compartment walls) and to the
sealing of punctures caused by fasteners.
INSULATION
• Location
- above / between / below
(or any combination)
• Selection
- thermal performance
- water vapour permeability
- water resistance (absorption)
- user friendliness
• Thickness
• Installation
- thermal integrity
- convection tight
Location:
(a) over the rafters
(b) between the rafters
(c) under the rafters
or any combination of these
Note : Option (a) is sometimes referred to as a “warm” roof construction or as
“sarking” insulation.
All options can be used for new roof constructions or where the roof is to be
replaced from rafter level up.
Only options (b) and (c) can be used in situations where the roof covering cannot
be removed or replaced.
Selection:
Rigid, semi-rigid and flexible insulants can be used. Each has its own specific
physical characteristics as regards performance and installation requirements the manufacturers’ recommendations should be followed.
cont ->
Thickness:
The thickness of the insulation will be determined by the required thermal
performance as well as by the roof construction (see Approved Document
L). It is important to ensure the continuity of the thermal insulation. If this
is broken eg by the rafters and /or penetrations through the roof, the
resulting thermal bridges can increase the risk of localised condensation
and pattern staining of ceilings at rafter line.
Note: Building Regulations require the effect of thermal bridging to be
taken into account when calculating the thermal performance (U-value) of
the roof. Refer to BS 5250 Section 9.6 and BRE Document 262: Thermal
insulation - avoiding risks.
Installation:
Thermal integrity is essential.
The roof void should be completely insulated. For example gable end
walls will need to be insulated to their full height.
The designer should take care to ensure that there are no gaps or breaks
in the insulation envelope.
The insulation should be installed to fit tightly at ridges, at eaves and
around penetrations. Seal if necessary with flexible (polyethylene) or PU
foam.
Insulation boards should fit tightly together with no gaps around them.
Rigid board joints should be correctly positioned so as to shed any likely
incoming external water. Some types of board will require their joints to
be sealed with tape - refer to the manufacturers’ instructions.
Special care needs to be taken with rebated boards designed for over and
between rafter installation e.g Roofmate PR to ensure that the rafter
spacing is accurately set out so as to avoid gaps or unnecessary cutting of
boards.
Convection tight/airtight:
A roof system in which the free movement of air through any section of the
construction is prevented by use of airtight joints and seals is said to be
“convection tight” or “airtight”.
INSULATION
- typical physical properties
XPS
Thermal conductivity
Water vapour resistance
(relative to MF)
W/mK
PUR
MF
0.025 0.036 0.024 0.036
140
60
80
1
Water vapour resistivity
MNs/gm 1000
300
600
5
Water absorption
% vol
0.3
6
3
?
Compressive strength
kPa
300+
190
max
175
max
120
max
Density
kg/m3
30
15-30
30
180
• XPS
EPS
PUR
MF
-
EPS
- extruded foamed polystyrene
- expanded foamed polystyrene (bead board)
- polyurethane/polyisocyanurate
- mineral fibre
• Thermal conductivity
XPS, EPS measured at 90 days (after equilibrium reached) - long term value.
PUR measured immediately after production ie before equilibrium
reached - short term value.
• Water vapour resistance
Determined relative to MF(air) for equivalent U-value thicknesses (XPS=50mm)
• Water absorption
Be sure to take into account likely effect on thermal conductivity !
ROOFMATE* RL, PR
- physical characteristics
Density
Thermal conductivity
Compressive strength
Water absorption
Water vapour resistivity
kg/m3
W/mK
kN/m2
% vol
MNs/gm
Board size
Thickness
Edge profile
mm
mm
-
PR
34
0.025
300
0.3
940
RL
34
0.025
300
0.3
940
2500 x 600
80, 90, 120
rebated
2500 x 600
35, 50
tongue &
groove
• Roofmate RL
Tongue and groove on all sides.
Board should be laid so the tongues in horizontal joints face up the slope.
• Roofmate PR
Available with edge flanged to suit 38 and 50mm rafters - type 38 and 50
respectively.
Boards should be laid so that horizontal lap joints (i.e top and bottom of boards)
point down the slope so that boards higher up the roof overlap those further
down (boards are marked so as to facilitate this e.g with an arrow pointing up the
slope of the roof).
UNDERLAYSREQUIREMENTS
- TRADITIONAL
• Keep water (snow, dust) out
• Air tight
• Adequate strength
- WATER VAPOUR PERMEABLE (Breather)
• As Traditional
plus water vapour permeability
• Keep water etc. out - secondary defense against wind driven rain,
snow and dust.
• Air tight
- to reduce wind load on primary roof covering.
• Adequate strength - tensile, tear strength (for nails), extensibility
(reduce movement under wind pressure).
Working temp. range - 20 to + 80 deg C.
• Water vapour permeability
- Traditional underlay
e.g BS747 Type IF felt
These are defined (BS5250) as having a water vapour resistance in
excess of 50MNs/g
- Water vapour permeable (breather) underlay
BS 4016 : 1995 Flexible building membranes (breather type)
- max. water vapour resistance 0.6MNs/g
BRE Thermal Insulation : Avoiding risks - specifies 0.1 - 2.0 MNs/g.
UNDERLAYS
WATER VAPOUR RESISTANCE
Traditional
MNs/g
50 - 270
420
BS 747 Type IF felt
Monarfil* 250
Breather
Permo*
Tyvek* HD - Soft
Tyvek* 2001 - Pro
Roofshield*
Monarperm* 450
0.20
0.24
0.16
0.08
0.11
Insulation
XPS - 90mm
PUR - 80mm
MF - 115 mm
85
46
0.6
* Tradenames
• Monarfil 250
-
reinforced polyethylene (0.25mm)
• Permo
- laminated spunbond polypropylene
• Tyvek Soft
- spunbond polyethylene (0.19mm)
• Tyvek Pro
- spunbond polyethylene / polypropylene
laminate (0.42mm)
• Roofshield
- spunbond polypropylene laminate (0.60mm)
• Monarperm 450 - spunbond polypropylene (0.45mm)
BREATHER UNDERLAYS
Performance criteria should reflect “real life” roof
conditions
• Water vapour permeability + water resistance
•
- working conditions
•
- compatibility
•
- “tenting”
•
- “blinding”
• Installation
• Roof conditions : - 20 to +800C, 0 to 100% RH, seasonal, daily,
hourly changes
• Compatibility
- specifically with timber preservatives - water
( surfactants ) vs solvent based ( swelling )
cause loss of performance.
• “Tenting”
- a problem with the early materials. Underlay
leaks when touching surface below.
• “Blinding”
- by dust, ice (?)
• Installation
- laid direct on insulation (common practice in
North)
- can cause noise (ie wind flutter ) ?
or
- supported on counterbattens(common
practice in South)
- userfriendliness => slipperiness underfoot
for roofer !
BATTENS
●
Tiling, counter
●
Dimensions
●
Location of underlay
●
Securement
• When the insulation is installed over the rafters, counter-battens will
be required to secure the insulation to the rafters and to provide
drainage under the tile battens - refer to BS 5534 Part 1 Section
3.6.3.2.
• Care should be taken to ensure that the construction techniques
employed provide for adequate and accurate location of the fixings
used to secure the battens and counterbattens to the rafters.
• Width determined by diameter of fasteners (10 - 11 x diameter)
• Thickness determined by method of securement
• Underlay can be in direct contact with surface of insulation or
located above the counter battens
• Who installs what ?
Carpenter
Roofer
-
up to and including counterbattens
(rafters, insulation)
- above counterbattens
(underlay, tile battens, tiles)
or from the rafters up
(insulation, battens, underlay,tiles)
SECUREMENT
-
need to secure tiles/slates, underlay and
insulation against dead wind and imposed
loads
•
Insulation
consider: - thickness (over rafters),
physical properties
•
Fasteners
eg BS 1202 nails, Helifix Inskew, Proctor PR nails
consider: - penetration, pull-out strength,
deflection under load
- ease and accuracy of installation
Refer to manufacturers for advice
SECUREMENT cont
When the insulation is installed over the rafters the fasteners securing the
counter battens or battens through to the rafters must be of sufficient strength
and length and correctly spaced so as to resist dead, wind and imposed
loads.
The following should be considered:
• Site locality - the assessment and determination of wind and imposed loads
• Roof Construction - roof pitch, rafter spacing, depth and width, insulation
thickness; batten/counter batten length, width and depth; fastener diameter,
length and spacing.
• Materials and related properties - slate/tile weight; rafter and
battens/.counter battens: timber specification; fasteners: pull-out and pullthrough strengths, shear strength and deformation under load characteristics.
• Consideration should also be given to the deflection and possible
overloading of the fasteners under load down the slope of the roof. It is
recommended that the deflection should not exceed 3mm. A fastener must
be capable of withstanding the dead and imposed loads vectored down the
slope of the roof i.e its maximum allowable bending stress must not be
exceeded - refer to the fastener and insulation manufacturers for advice. It
may be necessary to provide stronger and larger diameter fasteners (with a
corresponding increase in batten and rafter dimensions) or a reduced
spacing and/or stop battens (i.e parallel to the eaves/ridge)
Note : The trend towards increased thickness of insulation with reduced
U values (June 2000 proposals to change Approved Document L).
Securement cont
!
!
!
!
!
!
BS 6399 : Part 1 : 1996 Deadloads
BS 6399 : Part 2 : 1995 Wind uplift
BS 6399 : Part 3 : 1988 Imposed Loads
BS 5268 : Part 2 : 1996
BS 5534 : Part 1 : 1997
BS 1202 : Part 1 : 1994
use above to determine fastener size
and density ( per m2)
Note:
Designers must take into account the two loading conditions for
the fasteners:
• Wind uplift on the roof.
• Resistance to slip (deflection of the fastener) down the slope dependant on the pitch of the roof and the dead and imposed
loading. Insulation should not be considered to be a structural
material.
Refer to manufacturer’s literature for the specialist fasteners.
Fasteners
- method of securement
Tile battens
nailed to counter battens
Tiles
Counter battens nailed to
rafters through insulation
Rafter thickness
• Figure above shows a method of securement for insulation laid
over and between the rafters, in this case Roofmate PR.
• Counterbattens 32 mm thick secured with galvanised slab
nails 100mm long x 3.35 mm dia spaced at 200 and 150 mm
centres for duo and mono pitched roofs respectively - refer to BS
5268 : Part 2 : 1996.
• Tiling battens are secured with galvanised slab nails at the
required gauge - refer to BS 5534 : Part 1: 1997.
BUILDING REGULATIONS
• Building Regulations 1991, amended 1994
- Requirement LI : Conservation of Fuel and Power
“Reasonable provision shall be made
for the conservation of fuel and power
in buildings by limiting the heat loss
through the fabric of the building”
BUILDING REGULATIONS
Approved Document L
Maximum U-values (W/m2K)
DWELLINGS
SAPDocument </=
Approved
L :601995 U->60
Cold roof
0.20
0.25
values Warm roof
0.20
0.35
OTHER BUILDINGS
Cold roof
Warm roof - residential
- others
0.25
0.35
0.45
• If roof slope is greater than 70o then max U = 0.45 W/m2K
• For building classification see Approved Document B
• Building Regulations specify maximum allowable U-values the optimum cost effective U-values are in fact lower eg:
Floors
Roofs
Walls
W/m2K
0.35
0.20 - 0.25
0.30 - 0.35
BUILDING REGULATIONS
CONDENSATION
Approved Document F:1995
“Adequate provision shall be made to prevent excessive
condensation in a roof”
but …. Is based on traditional underlay experience
therefore …..
refer to:
BRE Thermal insulation : avoiding risks 1994
- see Section 2.7 - 2.10 ‘Sarking insulation’
BS 5250 1989
-see Clauses 9.1, 9.2 and 9.3
CONDENSATION - it’s prevention
• Short, long term concerns
• Insulation
- continuity, convection tight, performance
• Underlay
- choice, performance
• Roof covering (tiles/slates)
- air permeability (?)
• Ventilation
YES - between underlay/roof covering
YES - between insulation/traditional underlay
NO - between insulation/breather underlay
Control of condensation is of particular concern for those roof
systems where a breather underlay is used without a ventilated
airspace between it and the insulation. It is recommended that a
condensation risk analysis is undertaken - refer to to BS 5250.
Use of the criteria for condensation build-up within the roof system
as detailed in BS 6229 : 1982 (Section A.2.5.5.) is recommended.
The roof system below a breather underlay should be designed
and installed so as to be convection tight as is possible throughout
its design life.
Consideration should be given to installing a VCL on the warm
side of insulation if the insulation has a low water vapour
resistance - refer to the insulation manufacturer for advice.
cont ->
For buildings with high internal temperatures and humidities it is
recommended that a VCL be installed and for exceptional conditions,
as may be experienced in say swimming pools, laundries, that the
advice of a design specialist be sought.
Ventilation
- defined as “ the controlled movement of air”
There are two air spaces to be considered:
Between the underlay and the insulation
For traditional underlays ventilation should be provided in
accordance with the recommendations given in BS 5250 and
Approved Document F2 (1990). For breather underlays ventilation is
not normally required.
Between the roof covering and underlay
Where a traditional underlay is used it is not normally necessary to
provide ventilation.
Where a breather underlay is used without ventilation between the
underlay and insulation it will be necessary to ensure that there is
adequate ventilation. This may be provided through the slate/tile
assembly. Apertures for ventilation can be provided at the eaves,
ridge or incorporated into the slate/tile assembly - refer to BS 5250 for
ventilation aperture sizes.
NOTE: Ventilation through the slate/tile joints may not be sufficient
due to the close fitting of the slates/tiles. There may also be a risk
that the joints become blocked by vegetation or dust over the lifespan
of the roof. Additional ventilation inlets or outlets may, therefore, be
required. Particular attention should be given to long span roofs to
ensure that adequate ventilation is provided.
BUILDING REGULATIONS
FIRE
APPROVED DOCUMENT B : 1992
EXTERNAL FIRE SPREAD - B4
BS 476 : Part 3 : 1958
AA (best) rating - tile/slate roofs
- unaffected by insulation
INTERNAL FIRE SPREAD - B2
BS476 : Part 7 : 1971
Class O rating - 13mm plasterboard
• BS476 : Part 7 External fire exposure roof tests
• BS476 : Part 1 Surface spread of flame test
- lists Classes 1 (highest) to 4; XPS is unclassifiable
Class O is not identified in BS476. However, it can be
achieved by materials of limited combustibility
e.g plasterboard or a Class 1 material which has a fire
propagation index (I) < 12 and a sub-index (I,) < 6.
•
For useful information on aspects of XPS in building
applications see BS 6203 : 1989
INSULATED PITCHED ROOFING
In summary:
• Warm roof concept
15 + years proven track record
minimal condensation problems
secure
• Design for the total system
• Pay attention to the design of details*
• Take care in installation
The issues:
• Insulation - location, selection, installation
• Underlay
- selection, performance, installation
• Condensation - its prevention
• Securement
* see end of tutorial for typical details
Case study - Hospital
Extension - 2600m2 insulated pitched roof
• Architects:
Watkins, Gray International
• Main contractor:
J Longley & Co.
• Insulation installer:
NH Etheridge Ltd
• Roofer:
Cobsen, Davies
• Location:
Conquest Hospital, Hastings,
East Sussex
BUPA extension - completed 1998
• Project:
Case study - Hospital
! Insulation: Roofmate* PR Type 50 (90mm)
! Roof space for services - heating,
ventilation
Case study - Hospital
! Underlayer:
Tyvek 2001-B Pro
(over counterbattens)
! Securement:
Helifix Inscrew 600
fasteners - 110mm long
! Tiles:
Marley Modern
Case study - Hospital
U-value calculations
Tiles
Vented airspace
Tyvek 2001-B Pro
Unvented airspace
Roofmate PR
Plasterboard
U-value = 0.25 W/m2K
Outside surface resistance
Concrete tiles
Vented airspace
(between tiles and sarking)
Tyvek 2001-BPro
Unvented airspace
Roofmate PR
Unvented airspace
Plasterboard
Inside surface resistance
Thickness
(mm)
8.00
90.00
13.00
-
Thermal Resistance
(m2K/W)
0.020
0.007
0.120
0.180
3.600
0.180
0.081
0.100
Case study - Hospital
Condensation risk
analysis
U-value: 0.25 W/m2K
Condensation build up
winter
0 g/m2
summer
0 g/m2
annual
0 g/m2
Red : Actual temperature profile
0
-10
Blue : dew point temperature
Condensation occurs where red and blue lines touch or
cross
10
Temperature ºC
•Notes:
•Element: Pitched roof, ceiling at rafter line, warm pitched roof
•Exposure: exposed
•Internal surface emissivity: high
•External surface emissivity: high
•Building use: hospital
•Environmental conditions Summer
Winter
•Internal temp ºC
25
25
•External temp ºC
18
5
•Internal humidity %
60
60
•External humidity %
65
95
•Construction
•Outside surface resistance
•Concrete tiles
•Vented airspace
•(between tiles and sarking)
•Tyvek 2001-BPro
•Unvented airspace
•Roofmate PR
•Roofmate PR
•Umvented airspace
•Plasterboard
•Inside surface resistance
Thickness (mm)
8.00
30.00
60.00
13.00
-
Vapour Resistance (MNs/g)
0.91
0.16
28.08
56.16
0.68
-
20
30
Warm pitched roof construction
- detailing
5
4
7
2
3
1
6
Warm pitched roof construction
Type A - insulation over and between
rafters - Roofmate PR
Counter battens
Vapour permeable
membrane
Tiling battens
Roofmate PR Insulation
Tiles
Rafter
A1- Eaves detail
Ensure continuity
of insulation
Set rebated edges of insulation
over rafters
A2 - Hip detail
Cut insulation
to line of hip and set over
support battens
Hip rafter
A3 - Roof window detail
Roof window
Counter batten
Cut insulation to fit tight against roof
window trimmers and seal with gap filler
A4 - Valley detail
Discontinuous edge batten to
allow drainage and ventilation
Cut insulation boards to
line of valley. Form rebate
to set over valley boards
Gutter lining on
separating layer
Set valley boards
between rafters
A5 - Ridge detail
Nail tiles to
battens
Nail tiling battens
to counterbattens
Nail counter
battens to rafters
Cut insulation to fit
tight at ridge and seal
with gap filler
A6 - Abutment detail
Fix batten in
gap between insulation
and wall
Insulation over and
between rafters
Underlay
A7 - Verge detail
Insulation set over and
between rafters
Flying rafter
Bargeboard
Warm pitched roof construction
Type B - insulation over rafters Roofmate RL
Counterbattens
Vapour
permeable
membrane
Tiling battens
Roofmate RL
Insulation
Tiles
Rafter
B1 - Eaves detail
Ensure continuity
of insulation
B2 - Hip detail
Cut insulation
to line of hip and set onto
support battens
Support
battens
Hip rafter
B3 - Roof window detail
Roof window
Counter batten
Cut insulation to fit tight against
roof window trimmers and seal
with gap filler
B4 - Valley detail
Cut insulation
boards to line of
valley and set over
valley boards
Discontinuous edge
batten to allow
drainage and
ventilation
Valley rafter
Gutter lining on
separating layer
Set valley boards
between rafters
B5 - Ridge detail
Nail counterbattens to rafters
Nail tiling battens to
counterbattens
Nail tiles to battens
Cut insulation to fit tight at ridge
and seal with gap filler
B6 - Abutment detail
Nail counter
battens to rafters
Plasterboard
ceiling
Nail battens to counter
battens
Lay insulation boards
over rafters
B7 - Verge detail
Plasterboard ceiling
Bargeboard
Make up piece of insulation set
over gable wall
INSULATED PITCHED ROOFING
Summarising :
• Warm Roof: 15 years proven
experience ! minimal condensation,
securement problems
• Design for total system
• Attention to detail design
• Care in installation
Issues :
• Insulation selection, performance,
installation
• Underlay selection, performance,
installation
• Condensation: it’s prevention
• Securement
If the following questionnaire is successfully completed and sent to Dow Construction
Products, 2 Heathrow Boulevard, 284 Bath Road, West Drayton, Middx UB7 0DQ
Fax Number 0208 917 5413 a CPD certificate will be forwarded to you.
1. In the “warm roof concept” the insulation is placed
above the rafters
between the rafters
above and between the rafters
between the rafters
2. If a pitched roof is insulated at rafter level (and the loft space is to be utilised)
What are the maximum allowable U-values
0.25
0.35
0.45
Domestic Buildings (SAP>60)
Non-Domestic
- Old Peoples Home
- Office
3. What is the difference between a “traditional” and “breather” underlay
Water tight
Air tight
Tear Strength (nails)
Tensile properties
Water Vapour permeable
4. Where would you provide ventilation in a pitched roof construction insulated at rafter
level if a) a traditional or b) a breather underlay is used ?
(a)
Below rafters
Below insulation
Between insulation and underlay
Between underlay and tiles/slates
(b)
5. Which properties are of particular importance for breather underlays ?
Water resistance
Water vapour resistance
Compatibility with timber preservatives
Tear strength
Tearing resistance
Slipperiness
Blinding resistance
Colour
Air tightness
6. In designing a pitched roof which standards should you refer to for
1
General design - slating/tiling
Wind loads
Design - timber structure
Dead loads
Imposed loads
1 = BS 6399 : Part 1
2 = BS 6399 : Part 2
3 = BS 6399 : Part 3
4 = BS 5534 : Part 1
5 = BS 5268 : Part 2
2
3
4
5
7. Where would you go for advice on how to avoid condensation in a pitched roof ?
BS 5250
Approved Document L
Approved Document F
BRE 262 Thermal Insulation : avoiding risks
BS 5534
Insulation manufacturers
8. In a “warm roof construction” what issues did you need to consider to avoid/reduce
the risk of condensation. ?
Use of a vapour control layer
Water vapour permeability of insulation
Convection tightness of insulation layer
Type of underlay
Location of underlay
Where to ventilate
Air permeability of primary roof covering
Drying our of building structure
Attention to details e.g. at eaves
Securement of underlay
9. What factors must be considered when selecting and specifying fasteners ?
Length
Diameter
Pull-out strength (from timber)
Bending stress
Ease and accuracy of installation
Deflection under load
Width of battens, rafters
10. Which of these should be considered when selection of insulation for
installation or rafter level ?
Location
Compressive strength
Rigidity
Water vapour permeability
Water resistance
Thermal conductivity
Ease of installation
Fire resistance
Nail ability
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