Drain Land Defense Keeping Roof Drains Free and Clear

May 15, 2004

July 2004 Interface • 39
The old saying, “an ounce of prevention is
worth a pound of cure” can hardly be
argued when it comes to good roofing
practices. In this case, the problem to prevent
is a clogged roof drain due to build-up of
debris, leaves, and/or snow and ice around
the strainer. A rarely used yet low-cost cure is
to have a simple “drain guard” surrounding
the drain to help keep it free and clear from
The problems – degradation
and excessive weight
Many types of membranes will either
degrade or become damaged from ponding
water and vegetation growth and will weaken
the roof system’s integrity. All efforts should
be made to include positive drainage. This is
clearly stated by such nationally recognized
organizations such as the National Roofing
Contractors Association (NRCA), the Asphalt Roofing Manufacturers
Association (ARMA) and the EPDM Roofing Association (ERA).
Not only does ponded water damage waterproofing membranes, but the
added weight of the water stopped by a drain loaded with debris such as
leaves, trash, roofing material such as ballast and melted asphalt, and
snow and ice can dramatically increase load on the roof deck and possibly
induce collapse.
Maintenance program a nice idea, but…
A regular roof inspection and maintenance program to extend the life of
the roof system and to avoid catastrophe is a great idea and one of the best
preventive measures available. According to SPRI (Sheet Membrane and
Component Suppliers to the Commercial Roofing Industry), “Periodic preventive
maintenance can prevent small, easily-handled problems from
becoming disruptive, big budget nightmares.” At the top of the list for a roof
maintenance checklist, it recommends owners “keep roof clean and free of
debris” and “keep drainage systems clear and functional.” This type of a
preventive measure is talked about but often sidestepped. An added pre-
This photo shows a partial roof collapse from excessive weight of ponded water due to a
clogged drain strainer.
The roof drain shown here is dangerously clogged with
debris, an all-too-common condition.
ventive measure, however, can help to
keep the drain from clogging with or without
a maintenance program.
Send in the guards
According to the NRCA’s Roofing and
Waterproofing Manual – Fifth Edition,
“Because every roof has its own set of
drainage criteria, either the
architect/designer or the structural engineer
is responsible for including proper
drainage provisions in the roof system
design.” The Roofing Industry Educational
Institute states, “Coal tar bitumen roofs
must have special design care to avoid letting
the bitumen get into the drain pipes.”
Beyond these statements, the design community
is left with the question, “What can
be done to improve drainage on a roof?”
The answer – send in the guards – is a simple
and low-cost way to improve drainage
by blocking rooftop debris from clogging
the strainer.
Whether the debris is roof ballast,
gravel, leaves, or snow and ice, solutions
are available. Depending on the situation,
a roof’s needs can be addressed with various
metal forms that surround the drain –
typically in 4′ x 4′ or 3′ x 3′ square designs
with either perforated or slotted holes to
allow drainage but hold back debris.
(EDITOR’S NOTE: Specification of an
overflow drain or scupper to handle any
potential backup or clog of the roof guard is
also recommended.)
Minimal cost/ maximum payoff
Recommendations are made with good intentions. But the
design community has little control over whether or not building
owners institute a maintenance program. In the design of the roof
system, at least some control can be made by putting simple and
efficient safeguards in place. An ounce of prevention really can be
worth a pound of cure and more. ■
Asphalt Roofing Manufacturers Association, “The Effects of
Ponding Water,” Technical Bulletin, Calverton, MD, May
EPDM Roofing Association, “Frequently Asked Questions About
EPDM,” www.epdmroofs.org/faq/faq_installation.html,
Alexandria, VA.
Above: This roof drain detail, courtesy of the NRCA’s Roofing and
Waterproofing Manual – Fifth Edition, clearly shows a gravel stop
within a modified bitumen roof membrane system.
Right: This photo shows a “guard” with drainage slots in action,
keeping ballast and debris away from the drain strainer.
40 • Interface July 2004
July 2004 Interface • 41
Hogan, Lyle D.,
“Elements of
a Collapse,”
I n t e r f a c e ,
pg. 32-34,
March 1996.
Lewis, H.Z.,
P.E., “Build
To Maintain
– Proper
Design And
Care Can
Help Roofing Systems Meet
Your Expectations,” The Roofing
Industry Educational Institute,
National Roofing Contractors
Association, Roofing and
Waterproofing Manual – Fifth Edition, Rosemont, IL, 2001.
SPRI, “How To Implement A Roof Maintenance Program,”
www.spri.org/news_5.html, Waltham, MA.
Left: The precision-formed, 4′ x 4′
aluminum gravel stop shown here is
designed to prevent the flow of coal tar
pitch and gravel from clogging the drain
strainer during times of high temperature.
Dan Genovese is the OlyFlow Product Manager for Olympic Fasteners. The OlyFlow product line incorporates both the U-Flow and
RAC drains and accessories, both acquisitions of Olympic. Genovese has worked with the Retrofit Drain Task Force at SPRI, which
has recently completed the U.S.’s first national standard for retrofit roof drains. Dan has worked for Olympic for seventeen years.
Right: This photo shows
a gravel stop in action
keeping gravel and coal
tar pitch away from the
drain strainer.
America’s first national standard for retrofit roof drains, developed
by SPRI, was approved in early April as a national standard in
accordance with protocol established by the American National
Standards Institute (ANSI). This new standard is designated
ANSI/SPRI RD-1, 2003, “Standard for Retrofit Roof Drains.”
SPRI, the association representing sheet membrane and component
suppliers to the commercial roofing industry, developed this
roof drain standard to fill the information void regarding retrofit
John Hickman, chairman of SPRI’s Standards Task Force,
explains, “While the national plumbing codes have established
standards for new roof drains, there have been no guidelines for
what to do with an existing roof upon which retrofit drains are to
be installed.”
The main differences between retrofit drains and new ones,
Hickman notes, stem from the need to place them where existing
drains already are installed. This means that capacities must be
checked and the connection to existing plumbing must be leak-free.
Retrofit drains, by their very nature, have smaller drainage
diameter than the original drains, Hickman adds, because they
must fit inside the existing plumbing. Assuring sufficient capacity
depends upon the retrofit drain diameter, the number of drain sites,
and the rainfall expectations for the building location
Therefore, this new retrofit roof standard features a test protocol
designed to assure a leak-free connection to existing piping.
Also included are methods intended to calculate sufficient
drainage. An Isopluvial map (Rainfall Rate Map) of the continental
U.S. shows maximum one-hour rainfall values with a 100-year
return rate (“100-year rain”).
ANSI/RD-1 was officially canvassed in accordance with protocol
established by the American National Standards Institute
(ANSI). SPRI earned its certification as an official ANSI canvasser in
1994. For more information, visit SPRI’s web site at www.spri.org.