The Fundamentals of Siphonic Roof Drainage System Design

The Fundamentals of Siphonic
Roof Drainage System Design
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Learning
g Objectives
j
At the conclusion of this course,, the design
g professional
p
will be able to :
 Describe the basic principles of a siphonic roof drainage systems
 List the benefits of siphonic roof drainage and how the system selfselfprimes
 Compare and contrast the differences between traditional drainage
and engineered
g
siphonic
p
roof drainage
g
 Explain several myths and misconceptions as related to
roofing/drainage
 Reference the codes and standards relating
g to siphonic
p
systems
y
 Explain the role of the Licensure as it relates to health, safety, and
welfare
 Name and understand the components
p
of a siphonic
p
roof drain
Learning
g Objectives
j
At the conclusion of this course,, the design
g professional
p
will be able to :
 Illustrate how a siphonic system works with different roof designs and
as a controlled flow system
 Site case studies and installation examples where a siphonic system
benefited the owner
 Describe
D
ib h
how a siphonic
i h i system
t
can help
h l reduce
d
costs
t d
during
i hi
historic
t i
renovation projects
 Incorporate a siphonic design into a building to help acquire LEED
points:: (1) for the use of recycled material (cast iron), (2) by reducing
points
site preparation (less buried pipe), (3) by using a siphonic system in
conjunction with rainwater harvesting to reduce water use and
iimprove stormwater
t
t managementt on site,
it and
d (4) under
d th
the
“Innovation and Design” concepts by combining the concepts of
several LEED categories
Introduction
Siphonic
p
roof drainage
g is one of the newest technologies
g
to be
introduced into the American design field. Siphonic roof drainage
requires a certain level of technical analysis similar to engineered
automatic sprinkler systems and other mechanical systems. This
course provides training to the experienced design professional
f
to
impart the necessary knowledge for the understanding of siphonic
roof drainage operation and application.
Horizontal
H
i
t l Piping
Pi i saves
space within the building
The Concept
p



In a siphonic
p
roof drainage
g system,
y
siphonic
p
roof drains engage
g g a
specially engineered and tested roof drain baffle. This baffle allows
and sustains negative atmospheric pressure in the connected
piping and inhibits the admission of air into the piping system hence
sustaining full
full--bore flow and higher flow volumes and velocities.
The hydraulic balance in a siphonic roof drainage system is
achieved by a design professional employing hydraulic calculations
to ensure that the piping system fills up automatically in cases of
moderate to heavy precipitation. The resulting fullfull-bore or siphonic
action allows for
f the installation off horizontal, i.e. level, drainage
manifold piping serving multiple roof drains.
Siphonic
S
p o c roof
oo drainage
d a age systems
sys e s a
are
e po
powered
e ed by a
and
dd
discharged
sc a ged to
o
grade by means of a vertical stack into the point of discharge
through the influence of gravity making them true gravity systems.
Outline

This continuing education course is intended to provide
information on the background, operation and design of
siphonic roof drainage systems.
 The course covers the underlying hydraulic theory and
discusses the design advantages of a siphonic roof drain
system
t
such
h as in
i achieving
hi i LEED credit
dit and
d reducing
d i
installation costs.
 The course reviews various practical issues such as
authority approvals, product specification and existing
standards.
A Brief Overview
A Brief Overview

Siphonic Roof Drainage Systems
 The Siphonic Principle
 The
Th Benefits
B
fit
The Siphonic
p
Principle
p


The p
principle
p of the siphon
p
has been recognized
g
for ages.
g
A siphon
p
is
created by a tube or other type of conduit filled with the fluid to be
siphoned, thereby creating a continuous and closed path.
In any siphon, the discharge end of the conduit must be lower than
th llevell off th
the
the flfluid
id iin th
the source reservoir.
i At
Atmospheric
h i pressure att
the reservoir surface becomes the driving force pushing the fluid
through the tube to the lower point of discharge.
Siphonic Action
The Siphonic
p
Principle
p

Most examples
p
of siphons
p
include an inverted “U” shape,
p , this
configuration is necessary to lift the fluid out of the source reservoir
that cannot be tipped, much like a car’s gas tank. However, the actual
path of the siphon tube is irrelevant to the fluid’s ability to flow.

In the practical case of siphonic roof drainage, the drainage piping is
installed in the simplest way possible: flat and level
level. This allows the
piping to drain when it is not raining and then to prime full into a
continuous and closed path on its own during a rain event.
Overview of Siphonic
p
Drainage
g




“Closed” Outlets.

The roof drain has an air baffle that
promotes “full
“full--bore” flow.
Horizontal p
piping
p g is not p
pitched.

Flow is induced by natural hydraulic
action of siphoning.
When system
y
primes,
p
the p
piping
p g
depressurizes.

Atmospheric pressure pushes the
water into the drains with a force of
14 7 pounds
14.7
d per square ffoot.
t
Capacity is determined by the piping
system and the height of the roof above
the point of discharge.
discharge

Makes full use of gravity (i.e. potential
energy).
Siphonic Roof Drain
Overview of Siphonic
p
Drainage
g




Piping
p gp
primes and operates
p
100%
% full ((i.e. fullfull-bore flow).
)
Water is drawn through the outlets and piping faster than gravity
“channel flow” alone due to negative pressure.
Lower material expenditures due to smaller pipe diameters
diameters.
Pipe inverts leaving the building are at a minimum, making deep
trenching on the site beyond the building unnecessary.

Thi is
This
i an advantage
d
t
when
h developing
d
l i LEED certified
tifi d projects.
j t
Siphonic Roof Drain and Horizontal Piping
Benefits of Siphonic
p
Design
g


The major
j benefit of siphonic
p
roof drainage
g is the reduction in p
pipe
p
diameter to achieve the same volumetric flow of water off of a roof.
This is achieved by exploiting the kinds of flow patterns and behaviors
of the flow of water through
g p
pipes
p that result in p
pressure fluctuations
and priming to a full bore condition. These behaviors are systematically
avoided and prevented in the design of traditional sanitary drainage
and roof drainage systems.
Ideal siphonic drainage applications include factories, warehouses,
airports, convention centers, stadiums and “big“big-box” retail.
Horizontal Piping Saves Space in Ceiling
Warehouse application
A Siphonic
p
System
y
A Siphonic System

The Self-Priming Process
 How it Differs from a Traditional
Drainage System
 Myths and Misconceptions
The Self
Self--Priming
g Process in a Siphonic
p
System
y
Priming
g first occurs at the smaller diameter branch sections that
connect each roof drain to the main horizontal carrier pipe or manifold.
At this point, each siphonic roof drain acts independently as a miniminisiphonic system. As water accumulates in the manifold, air is purged
out off the
h point
i off discharge
di h
until
il the
h manifold
if ld and
d stack
k is
i 95%
9 % to 100%
full of water. The system is then completely siphonic and under
predominantly negative pressure.
Showing
Sho ing the flow
flo as pipe primes
How the SelfSelf-Priming
g Process is Achieved

Wavy flow (Pattern 1) is seen during rainfall events far below the
piping system’s ability to prime. Light showers will typically produce
this flow condition until rainfall intensity increases to a point where
branch pipes can fully prime.

The pulsating flow (Pattern 2) ordinarily happens at the junctions of
the branch pipes with the main collection piping. This is due to the
sudden decrease in pipe velocity as the water transitions from the
smaller diameter branch pipes to the larger main collection pipe.
pipe

At this juncture, a hydraulic jump occurs as the fluid transitions from
super--critical to subsuper
sub-critical flow. Eventually the peaks of these
hydraulic jumps come in contact with the crown of the pipe. This is
where the plug flow intensity pattern (Pattern 3) become prominent.
How the SelfSelf-Priming
g Process is Achieved

As the pipe continues to prime, the higher flow velocity of the water
captures and emulsifies the remaining air and a frothy “bubble” flow
forms (Pattern 4).

The frothy flow condition becomes gradually clearer until all of the
remaining air is purged out of the point of discharge. This is the fullfull-bore
flow (Pattern 5) created by siphonic action.
action

It is rare that a rainfall event will occur at the exact design intensity (Id)
for any
an sustained
s stained period
period. Therefore,
Therefore a system
s stem will
ill typically
t picall experience
e perience
flow Patterns 3 to 5 during heavy rainfall. During light rainfall events,
Patterns 1 and 2 may develop.
The Differences Between Traditional Drainage
and Engineered Siphonic Roof Drainage

A Traditional System
As seen in illustration 1, a traditional gravity drainage system
consists
i
off a networkk off rooff drains
d i connected
db
by open outlet
l to a
vertical downpipe. The pitch in the piping allows rainwater to flow to
a discharge point. This configuration necessitates relatively large
diameter stacks which connect into an even larger underground
drainage network.
The Differences Between Traditional Drainage
and Engineered Siphonic Roof Drainage

A traditional rainwater p
piping
p g system
y
is sized and p
pitched to be at
atmospheric pressure throughout. Since pressure is constant from inlet to
outlet, the only thing inducing flow is the pipe pitch.

In a horizontal pipe segment, illustration below, water cascades along the
invert of the pipe. About ½ of the pipe cross section is used to convey water
and the remaining ½ is air at the maximum expected rainfall rate. Since
conveyed water contains air
air, it works at only a fraction of its design
capacity.
The Differences Between Traditional Drainage
and Engineered Siphonic Roof Drainage

A Siphonic
p
System
y


Siphonic systems induce flow by creating a fullfull-bore continuous path of
water making pitch unnecessary, as seen in the illustration below. The
full--bore flow is achieved through natural hydraulic action and is not
full
produced by any sort of moving part
part, special fitting or control in the
piping network.
Si h i systems
Siphonic
t
d
do nott require
i any special
i l iinstallation
t ll ti kit or
procedure. The pipe materials and fittings used with siphonic roof drains
are the same as those required for traditional drainage systems.
The Differences Between Traditional Drainage
and Engineered Siphonic Roof Drainage


With a flat
flat, level design
design, long horizontal runs above overhead
ceilings are possible, as shown in illustration 4.
This reduces the amount of buried pipe and the associated costs
with
ith ttrenching,
hi
bedding,
b ddi
and
d backfilling
b kfilli within
ithi th
the b
building’s
ildi ’ ffootprint.
t i t
The Differences Between Traditional Drainage
and Engineered Siphonic Roof Drainage

Siphonic systems are designed to operate under subsubatmospheric pressure when primed full. The horizontal piping
in the system can have higher velocities. This means
rainwater is moved off
ff off the rooff faster
f
during the heavy
storms. During light rainfall events, the piping still drains but in
the traditional open channel flow mode.
 Siphonic roof drainage systems are more efficient in the use
of materials since smaller pipe diameters can be specified to
handle a wide range of rainfall events.
Myths
y
and Misconceptions
p






Myth 1: Siphonic systems drain water off of the roof “faster” than traditional
piping.
Reality: Although higher operating velocities are achieved, the drainage
capacity is a function of pipe size. They can drain as quickly or as slowly as
desired. Siphonic roof drainage is very good for controlled flow
requirements.
Myth 2: Siphonic systems have to be engineered by the manufacturer or
supplier
li off th
the pipe
i and
dd
drains.
i
Reality: A majority of the siphonic systems installed in the U.S. to date have
been engineered by independent consulting engineers.
Myth 3: The pipe and fittings are available only from foreign proprietary
sources.
Reality:
y Pipe
p and fittings
g used for siphonic
p
roof drainage
g systems
y
in the
United States are the same as those used for traditional plumbing systems.
There are no special manufacturers, materials or installers needed for
siphonic roof drainage systems.
Myths
y
and Misconceptions
p






Myth 4: There is standing water on the roof at all times in order to maintain
a siphonic operation, even while not raining (i.e.,
(
the pipe is always full).
f )
Reality: When it is not raining, the roof and piping are dry. When it rains, a
layer of water develops on the roof, but in the same way as with traditional
atmospheric systems. Actually, this layer of water is typically less for
siphonic systems.
Myth 5: Water builds up on the roof until a critical level is reached and then
th drains
the
d i ““open up”” tto siphon
i h th
the water
t off.
ff
Reality: Water build
build--up on a flat roof or in gutters is not any different than
traditional systems. Transition from partly full to full bore is a smooth
transition. This property is a tested parameter for siphonic drains (15
second rule). Also, the drains are fixed and without moveable parts.
Myth 6: There must be valves, utility connections or mechanical controls to
make
k the
th siphon
i h work.
k
Reality: There are no valves, controls, regulators or moving parts of any
kind. The system consists only of drains and piping. Siphonic systems prime
y
action.
due to natural hydraulic
Codes,, Standards & Licensure
Codes Standards & Licensure
Codes,
When designing a Siphonic Roof
Drainage Systems consideration should
be giving to the governing codes and
standards, and licensure agreement.

The two main governing codes and standards are:
 ANSI/ASME A112.6.9 “Siphonic Roof Drains”
 ASPE Technical Standard 100 “Siphonic
Siphonic Roof
Drainage”
 Other pertinent codes and standards should
be considered and reviewed
Codes and Standards

ANSI/ASME A112.6.9 “Siphonic
p
Roof Drains” – Siphonic
p
roof drain
performance testing is governed by ANSI/ASME A112.6.9.
 This standard establishes the testing procedures for siphonic roof
drains used to determine the product resistance coefficient, flow
range and
d response tto varying
i flflow rates.
t
Note: To be fully compliant with this standard, the drain must be marked with the
manufacturer’s name or trademark. Also the baffle plate and drain body must be
marked with the baffle plate model number, resistance coefficient and the words
“Replace Missing Baffle with Model XXX.”
The marking of the resistance coefficient makes it possible for an engineer to
determine the value of the siphonic roof drainage system and to identify the drain
manufacturer and proper replacement part number if a baffle is damaged or
missing

ASPE Technical Standard 45 “Siphonic Roof Drainage”
 This standard establishes the calculation procedures for siphonic
piping
p
p g systems,
y
, acceptable
p
p
pipe
p materials,, p
performance
requirements, and a set of “do’s” and “dont’s” necessary to avoid
pitfalls.
State Regulations
g
for Licensure

Background:
g
 Licensure of engineers and professionals at design firms is
regulated at the State level. Originally, past engineering disasters
prompted a few States to adopt laws regulating the practice of
engineering.
i
i
Th
The purpose off such
h llaws iis tto protect
t t th
the h
health,
lth
safety and welfare of the public. Licensed design professionals are
required to abide by a strict code of ethics to ensure adherence to
public safety.

Professional Firms:
 Most professional design firms have a Certificate of Authorization or
equivalent permit that demonstrates they are qualified to perform
engineering designs.
 If your company wishes to engage in a contract with a firm offering
to design siphonic roof drainage systems it is recommended that
you obtain that company’s Certificate of Authorization or permit.
This is particularly important if a roof drain product manufacturer or
sales representative offers to design siphonic systems as they may
not be able to certify the design.
Siphonic
p
Roof Drains
Siphonic Roof Drains





Drain Body
Flashing Ring
Ai B
Air
Baffle
ffl
Dome Strainer (Leaf Guard)
Governing Standard
Components
p
of a Siphonic
p
Roof Drain

Siphonic
p
roof drains are actually
y very
y simple
p devices. They
y include all
of the familiar components common to traditional roof drains. This
figure shows a cutcut-away of a typical siphonic roof drain with all its
required components.

The distinguishing feature of a siphonic roof drain is the air baffle.
baffle. This
air baffle is engineered and tested to prevent air from entering the
piping
g system
y
at peak flows. Other than the baffle, a siphonic roof drain
has the same features as a traditional roof drain including a drain
body, flashing ring, dome strainer, and fastening hardware.
hardware.
Components
p
and Function


The air baffle consists of a disc shape
shape. Most designs include fins or
blades that protrude from the bottom of the disc. They function as
straightening vanes similar in form and purpose as those used in antiantivortex plates used in pump suctions and other similar applications
applications.
The leaf guard, or dome strainer,
strainer, functions as a strainer or sieve to
trap foreign objects and prevent their ingestion into the drainage pipe
system.
Baffle
Plate
Fins
Plate
l
Ring
Components
p
and Function


The drain body provides a means of mounting the fixture to a roof deck
system. It also provides a spigot outlet connection for the attachment of
drainage pipe below the roof deck surface.
Th llower surface
The
f
off the
th flashing
fl hi ring
i has
h ab
beveled
l d surface
f
tto mate
t
with the outer top surface of the drain body. The inner rim has a
depression on the upper surface that receives the base of the air baffle.
Roof Drain Selection, Placement
and
dD
Design
i
R fD
i S
l ti
Roof
Drain
Selection,
Placement and Design

Flat Roofs
 Gutters
 Design Flexibility
 Recommended Discharge Designs
Flat Roofs


A Siphonic roof drain system and drain are ideal for “flat”
flat roof
construction.
The placement of the roof drains on “flat” roofs is normally dictated by
structural
t t l and
d rooff design
d i criteria.
it i Th
The pitch
it h off th
the steel
t ld
deck
k or th
the
maximum thickness of tapered insulation usually establishes the
maximum spacing between roof drains. These conditions are normally
determined by the structural engineer, architect and/or plumbing
engineer prior to the plumbing and drainage design being started.
Flat Roofs
Siphonic roof drainage systems do not present any other special needs
for roof drain placement, so the architect or engineer may locate the
roof drains per traditional standard practice.
Gutters


Gutters are not common in roof drainage
g design
g in the United
States. However, some buildings with certain architectural designs
may incorporate them.
Continuous gutters provide a good way to reduce the number of
drains and stacks that is otherwise not possible for flat, cricketed
roofs.
Design
g Flexibility
y

The flexibility in siphonic roof drainage system design exists on several
facets. Independence
p
of p
pitch allows for the design
g of horizontal runs
above ceilings and other spaces with overhead limitations. The
placement of stacks within a building is much more flexible as a result.

The physical properties of siphonic pipe design enable the design
professional to achieve innovative and effective designs. Changes can
be made to a siphonic system during construction but only under the
direction of the deign engineer who shall recalculate and approve the
proposed changes.
Recommended Discharge
g Design
g

In a siphonic designed system
system, the siphonic condition needs to
terminate before connecting to the storm sewer system.

The siphonic action can be terminated at any time simply by
increasing the lower horizontal piping out to the equivalent “gravity”
pipe
p
p size. When this p
pipe
p is tied into a manhole or catch basin, the
storm sewer sees no difference.

Th connecting
The
ti manhole
h l should
h ld b
be ventilated
til t d b
by some means.
This can be accomplished by installing an open grate instead of a
sealed manhole, or use a perforated manhole cover. When this is
not possible, a vent pipe can be extended from the manhole and
terminated above grade. This ventilation will prevent the possibility
of pressure fluctuations in the storm sewer system.
y
Case Studies, Savings and
I t ll ti
Installations
Case Studies, Savings and Installations





Installations
Case Study – 1, IKEA Store in
Paramus,, NJ
Case Study – 2, IKEA store in
Atlanta, Georgia
Savings Example – Vertical Stack
Savings Example – Horizontal
Piping
Single Point of Discharge
You’re Not The First –
Siphonic Installations
More than 650 million
square feet worldwide.
Nearly
y 7 million square
q
feet
in the U.S.
Case Study
y-1

Paramus,, New Jersey
y

The IKEA Store in Paramus, NJ

The first siphonic system installed in the United States.

In a value engineering exercise, it was determined that
• siphonic roof drainage would be less expensive
• plumbing engineer’s traditional design was replaced with an
engineered siphonic design.


Traditional design consisted of twelve stacks each ten to twelve
inches in diameter.
Siphonic
p
system
y
consisted of only
y six stacks ranging
g g from six to
eight inches in size resulting in a substantial savings in pipe and
fittings.
Case Study
y – 1 cont...

Demographics of IKEA Paramus








Roof Area (square feet) 250,000
Height
g ((feet)) 50
Design Rainfall Intensity (in/hr) 5.0
Number of Discharge Points 5
Total Discharge (cfs) 28.9
Number of Drains 23
Pipe Material ASTM A53 Schedule
10 Galvanized Steel with rollroll-groove mechanical couplings.
Case Study
y-2
Atlanta, Georgia



Located in the 138 acre Atlantic Station redevelopment site
Site was once the home to the Atlantic Steel Hoop Company.
This site posed two challenges
1. 230,000 square feet of roof surface on the site would have increased
th site
the
it runoff
ff rate
t and
d quantity
tit to
t the
th culvert,
l t which
hi h by
b currentt
standards is aged and nonnon-compliant with environmental regulations.
2. The connection to the culvert was difficult from a civil engineering
perspective.
p
p
•
The engineering solution
•
•
•
Underground detention tanks and pumps
Reportedly estimated at almost one million dollars in excess of initial
construction estimates
estimates.
The configuration of the site and position of the building made
access to this storm drainage system impossible by traditional
gravity methods.
Horizontal manifold of a siphonic roof drain system in a
warehouse. The roof drain branch ties into the manifold with a
lateral. This system runs level and parallel to the structure. The
overhead insullation eliminates roof drainage leaders at columns
and under slab trenching.
Case Study
y – 2 cont...
Atlanta, Georgia
 The implementation
p
of siphonic
p
roof drainage
g


Made it possible to drain the roof to the rear of the building where storm
drainage piping could be installed below the delivery access road and
off the site towards the retention pond.
IKEA realized savings with
•
•
•
•

The use of siphonic roof drainage inside the building
Saved significantly in site infrastructure costs
Avoided a lengthy permitting process
Contributed to the overall environmental revitalization of the area
Demographics of IKEA Atlanta

Roof Area (square feet) 226,000 roof, 61,270 parking deck

Height (feet) 35

Design Rainfall Intensity (in/hr) 3
3.7
7

Number of Discharge Points 5 from roof, 1 from parking deck

Total Discharge (cfs
(cfs)) 19.4 from roof, 5.25 from parking deck

Number of Drains 33 on roof,
roof 10 on parking deck

Pipe Material ASTM A888 NoNo-Hub Cast Iron with MG Couplings
Savings
g Example
p -1
Example 1:
 A vertical stack of a traditional roof drain system
y
is
designed to drain 63,940 square feet of roof surface at a
rainfall intensity of 3.25 inches per hour. According to IPC
2000, the required pipe diameter is 12 inches. At this
flow the pipe would be about 25 percent full and would
flow,
achieve a terminal velocity of 24 feet per second. Cast
iron pipe for this stack size would cost about $1,488.00
per 10 foot section.
p
 An existing siphonic system design covering the same
roof area and rainfall intensity has a calculated stack
diameter of 8 inches. The design velocity is 14 feet per
second
d and
d th
the pipe
i iis 100 percentt full.
f ll C
Castt iiron pipe
i ffor
this stack size costs about $627.00 per 10 foot section.

That’s a sa
savings
ings of $861
$861.00
00 per ten foot section for
this part of the system or almost 58 percent less than
a traditional design.

Based on R.
R S.
S Means Construction Cost Data 2005
2005. These cost
calculations are examples from real world applications; your cost
may be different. These costs are given for illustration only.
Savings
g Example
p -2
Example 2:
 A horizontal segment
g
of a traditional roof drain system
y
is designed
g
to drain
15,685 square feet of roof surface at a rainfall intensity of 3.25 inches per hour.
At a pitch of 1/8” per foot (about 1 percent), the required pipe diameter is 10
inches (IPC 2000, Table 1106.3). At this design flow, the pipe would be 52
percent full and have a velocity of 4.0 feet per second. Cast iron pipe with
hangers every 5 feet on center and a 1 inch fiberglass insulation cover and
couplings every 10 feet would cost about $1,057.00 per ten foot section. If
installed below grade, the cost is about the same if insulation cover is replaced
with the cost of trenching and backfill
backfill.
 An existing siphonic system design covering the same roof area and rainfall
intensity has a calculated pipe manifold of 6 inches. Even without pitch, the
design velocity is 6.1 feet per second and 100 percent full. Cast iron pipe this
size with hangers every 5 feet on center and a 1 inch fiberglass insulation cover
and couplings every 10 feet would cost about $515.00 per ten foot section.

That’s
at s a sa
savings
gs o
of $5
$542.00
00 pe
per te
ten foot
oot
section in this part of the system or about
51% less than a traditional design.
Controlled Flow System
y
Controlled Flow Systems

Function
F
ti off Pipe
Pi Sizing
Si i
 Roof Deck
 Allowance by Code
Controlled Flow Systems
y



Siphonic roof drainage systems are by their very nature
“controlled flow” systems. Therefore, the designer can set the
maximum flow capacity of the system through selection of the
design rainfall
f intensity.
The lower the discharge capacity, generally the smaller the
pipe diameters and drain sizes
sizes.
Any controlled flow roof drainage system is intended to detain a
quantity
y of water temporarily
p
y on the roof,, therefore,, the
certain q
roof deck should be designed to hold the intended distributed
load of water before the overflow point is reached.
Allowance by
y Code

Controlled flow systems
y
are becoming
g much more common as cities
and towns seek methods of reducing the impact of storm water runoff.

New York Cityy is an example
p of an area that commonly
y requires
q
controlled flow off of roofs because space for ground detention is not
available and storm sewer capacities are more and more maxed out.
Therefore, these systems are becoming incorporated into local and
model codes as engineered systems.
systems

Siphonic roof drainage tends to fall under this category. Since it can
essentially guarantee a limited discharge through pipe sizing
sizing, it poses
a more attractive solution to systems with flow control weirs at the roof
drains.
Historic Renovation and LEED
Historic Renovation and LEED

Disney C
Di
Case St
Study
d
 What is LEED
 How can siphonic drainage
systems help in achieving a LEED
certified project
 Rainwater Harvesting
Historic Renovation

Renovations to historic structures sometimes present
challenges to handling roof drainage.
 Typically, the roof drainage installed in an old building
does not meet current code requirements in terms of
rainfall capacity. It is often necessary to replace the piping
with a new system
system.
 Of course, there may be ceilings, walls and other
ornamental elements in the building that are best not
disturbed or very expensive to replace.
 The pipe size reduction and nono-pitch configuration of a
siphonic roof drainage system can be useful in minimizing
the impact on the building while providing for the higher
rainfall intensity.
Historic Renovation
Siphonic Roof Drain
Historical Building Retrofit Application
Problem

A historical Disney building in Pasadena, California was being
refurbished and needed a roof drainage system that allowed the
exterior to remain unchanged.

Th Architects
The
A hit t contacted
t t d a local
l
l manufacturing
f t i representative
t ti for
f
insight on using siphonic roof drains on the job.

The local ordinance required that the exterior of the 100 year old
building not be changed and that all overflow drainage be piped into
the city storm drainage system. Additionally, the job required a quick
and viable roof drainage solution.
Historic Renovation
Solution




The Siphonic Roof Drain was selected and used because the
overflow can be controlled to a specific point on the building. In the
original design there were no overflows in place so the siphonic
drains were the perfect solution to their problem.
The manufacturing representative showed the architect how the
siphonic action of the roof drains allow the piping system to be run
horizontal. This piping design enabled the overflows to be
evacuated on the side of the building.
The vertical
ertical stack
stack, once it reached the gro
ground,
nd was
as piped to a
vented manhole where water was discharged into the storm system.
This solution satisfied both the architect and the city of Pasadena.
Th Disney
The
Di
Pasadena
P
d
project
j t was a success with
ith th
the client,
li t th
the
architect, and the city officials; all were pleased that the siphonic
roof drain was able to solve their design problems.
LEED

LEED

In the context of the LEED rating system, siphonic roof
drainage contributes to the reduction in materials used by
allowing for smaller piping. And it facilitates the
achievement of LEED credits for the reuse of the existing
building.

Siphonic roof drainage is useful for the replacement of
exterior downspouts particularly along facades that must be
preserved due to historic value.

Siphonic roof drainage is environmentally friendly,
friendly enables
historic preservation, is easier to install, and saves money
that can be used on other renovation efforts.
U.S. Green Building Council (USGBC)/ Leadership
in Energy and Environmental Design (LEED®)

The LEED Green Building Rating System was devised as a
voluntary, consensusconsensus-based national standard for developing
high--performance, sustainable buildings.
high

LEED was initially created by the U.S. Green Building Council
(USGBC) to establish a common measurement to define “green
b ildi ” It has
building.”
h since
i
grown into
i t a program aimed
i d att raising
i i
awareness of and promoting integrated “green” building
projects.

To become LEED certified, a building is rated by six categories.
Within each category,
g y p
points are awarded based on the LEED
Green Building Rating System.
U.S. Green Building Council (USGBC)/ Leadership
in Energy and Environmental Design (LEED)

LEED p
points are not given
g
to individual products,
p
, but to an aggregate
gg g
of the building system that saves water, energy, and contributes to a
healthy indoor environment.

An example of this is WalWal-Mart’s use of green building designs on
a prototype
t t
store
t
i Dallas,
in
D ll
Texas.
T

One feature of the design is the capture of rainwater for use
throughout the building and grounds; i.e. rainwater harvesting.

By using Siphonic Roof Drains in a siphonic design, LEED points can
be awarded if the system is used for rainwater harvesting under the
Water Use Reduction and Innovation and Design credits
credits.
Possible Points in Using a Siphonic System with
Rainwater Harvesting
Stormwater Design, Quantity Control –
1 point. 50%
% postpost-development managing storm water runoff.
ff
Stormwater Design, Quality Control –
1 point. Storm water treatment systems designed to remove 80% of the
average annuall postpostt-development
d
l
t total
t t l suspended
d d solids.
lid
Water Efficient Landscaping, Reduce by 50% 1 point. Limit or eliminate the use of potable water for landscape irrigation.
Water Efficient Landscaping, No Potable Water Use or No Irrigation –
1 point. Use only captured rain or recycled site water use for site irrigation.
Innovative Wastewater TechnologiesTechnologies1 point. Reduce generation of wastewater & potable water demand, while
increasing the local aquifer recharge.
Water Use Reduction,
Reduction 20% Reduction –
1 point. 20% reduction in water use for building.
Water Use Reduction, 30% Reduction –
1 point
point. Maximize water efficiency within building to reduce the burden on
municipal water supply & wastewater systems.
Rainwater Harvesting
g
A siphonic
p
roof drainage
g system
y
is one of the most effective
technologies offered for capturing rainwater from a building roof top
to aid in implementing rainwater harvesting.
R i
Rainwater
t H
Harvesting
ti
Rainwater Harvesting
g
In a siphonic system, several roof
drain outlets can be connected to a
single vertical discharge pipe.
Fewer discharge points and no
requirement
q
for pitch
p
in the piping
pp g
means the rainwater can be easily
routed horizontally below the roof
t a storage
to
t
tank
t k or cistern.
i t
Rainwater Harvesting
g
The stored rainwater is now available for use in non
non--potable applications
such as toilets and urinal flushing, mechanical systems, custodial uses, and
for site irrigation.
One of the major benefits of designing a building with siphonic roof
drainage and rainwater harvesting systems is reduced overall construction
and facility operation costs.
Additional benefits include reduced discharge of rainwater to lakes,
streams, rivers and sanitary systems, and decreased dependence on
municipal water supplies.
Summary
y
Summary

Conclusion
C
l i
 Objectives Review
Conclusion

Siphonic roof drainage technology aids in eliminating a number of
factors associate with building design such as reduced site work
and a reduction in material costs.

The technology works well with rainwater harvesting as the piping
can be delivered to a single
g location and it enables the design
g
professional to include these attributes toward a project earnign
LEED certification.

Siphonic roof drainage systems offer a much more efficient roof
drainage solution.
Conclusion
Learning siphonic roof drainage design tends to “open our eyes”
t issues
to
i
nott commonly
l considered
id
d in
i rooff drainage
d i
design
d i in
i
general.
Course Summary
y
The design professional will now be able to:
 Describe the basic principles of a siphonic roof drainage systems
 List the benefits of siphonic roof drainage and how the system self
self--primes
 Compare and contrast the differences between traditional drainage and
engineered siphonic roof drainage
 Explain several myths and misconceptions as related to roofing/drainage
 Reference the codes and standards relating to siphonic systems
 Explain
p
the role of the Licensure as it relates to health, safety,
y and welfare
 Name and understand the components of a siphonic roof drain
Course Summary
y
The design
g professional
p
will now be able to:
 Illustrate how a siphonic system works with different roof designs and
as a controlled flow systems
 Site case studies and installation examples where a siphonic system
benefited the owner
 Describe how a siphonic system can help reduce costs during historic
renovation projects
 Incorporate a siphonic design into a building to help acquire LEED
points:: (1) for the use of recycled material (cast iron), (2) by reducing
points
site
it preparation
ti (l
(less b
buried
i d pipe),
i ) (3) b
by using
i a siphonic
i h i system
t
in
i
conjunction with rainwater harvesting to reduce water use and
improve stormwater management on site, and (4) under the
“Innovation
Innovation and Design
Design” concepts by combining the concepts of
several LEED categories.
categories.
The Fundamentals of Siphonic
Roof Drainage System Design
Course Sponsor
Jay R. Smith Mfg.
2781 G
Gunter
t P
Park
kD
Drive
i E
Montgomery, AL 36109
Phone: 334-277-8520
Fax: 334-272-7396
E-mail
salesengineering@jrsmith.com
Web
www.jrsmith.com
Course Number
JRS22A
Pl
Please
note:
t you will
ill need
d to
t complete
l t the
th conclusion
l i
quiz
i online
li
att
ronblank.com to receive credit
An AIA Continuing Education Program
Credit for this course is 1 AIA/CES HSW Learning Unit
This Program is also registered through ASPE
(American Society of Plumbing Engineers)