Replacing a Roof Drain on a Structurally Sloped Steel Roof Deck

Figure 1. Roof drain detail. Photos: Hutchinson Design Group Ltd.

What is the number one goal of any building owner when it comes to the roof? They don’t want water pouring through their ceilings damaging the interior of the building. How do you keep water out of the building? By keeping the water on the exterior of the building and directing it to the roof drains or other drain locations, such as scupper or gutters. The roof drain is, on a basic level, one of the simplest details on the roof, and yet it is flashed incorrectly time and time again. This paper will walk you through the process of replacing a roof drain on a structurally sloped steel roof deck and installing the new roof system and flashing.

Photo 1. The sump pan and drain body have been installed. Photos: Hutchinson Design Group Ltd.

First off, we are going to assume that the current drainpipe is adequate to handle the existing water volume and drain its portion of the roof, and that the drain pipe is in good condition. Our new roof system will meet the current R-30 requirements for continuous insulation above the roof deck in a roof near Chicago. So, our roof system will be composed of a mechanically fastened substrate board on the steel roof deck, a self-adhering vapor retarder, two layers of 2.6-inch insulation mechanically fastened, a 1/2-inch modified gypsum cover board set in bead foam adhesive, and fully adhered EPDM membrane. (See Figure 1.) We will also assume that the roofing contractor is acting as the general contractor for our scenario.

Now that we have our parameters out of the way, what’s first? I have never met a building owner that likes construction debris inside of their conference room or classroom, so the interior needs to be protected prior to the removal of the existing roof drain. This can be as simple as some Visqueen, but the interior protection needs to be installed prior to the removal of the existing roof drain. The one question that seems to come up is, who is installing this protection? The owner? The plumber? The roofing contractor? I like to put this on the plumber. He knows when he is removing the drain and installing the new one.

Once the interior protection is installed, we need to coordinate the removal of the existing roof system and installation of the vapor retarder with the removal of the existing roof drain, as well as the installation of the new metal sump pan, drain body and lead and oakum joint to the existing drain pipe. (See Photo 1.) This all needs to be done on the same day so that the roof can drain properly and that the vapor retarder can be terminated onto the roof drain flange. This part is critical, as with experience this designer has learned that the vapor retarder can be used as the seal between the extension ring and the roof drain flange and that the O-ring can be eliminated. The sump needs to be fastened to the roof deck around the perimeter at 8 inches on center and be centered on the drainpipe. The drain body then needs to be set over the drainpipe and lead and oakum installed between the drain body and drain pipe.

Installing the New Roof

So, now we have the roof drain body and the vapor retarder installed. Now comes the new roof system. To meet our R-30 requirements, we are going to need a base layer of 2.6-inch polyisocyanurate insulation and 4-foot-wide, 1/2-inch-per-foot tapered insulation sump around the roof drain. This sump will get us to the R-30 requirements of 4 feet from the roof drain as required by the current codes. If my math is correct, that will leave 3.1 inches of insulation at the roof drain. We will need a reversible collar and threaded extension ring to accommodate this height. When setting the reversible collar onto the drain bowl, set it in water cut-off mastic. If the drain ever becomes clogged, this will help to keep water from seeping under the reversible collar and into the roof system. Next the threaded extension ring is installed. First, install some water cut-off mastic onto the treads prior to engagement with the reversible collar. Once again, this will help to prevent water from entering the roof system if the drain becomes clogged and backs up.

Photo 2. The extension ring has been set lower than the cover board (yellow) and water cut off mastic has been installed on the extension ring flange. Photos: Hutchinson Design Group Ltd.

One of the main questions that I receive from the roofing and plumbing contractors is, “How high should I set the extension ring?” Well, it varies per roof system, but for our scenario it needs to be set flush with the top of the tapered insulation. We set it here because we have our cover board that has yet to be installed, and when the clamping ring is installed it will be lower than the cover board. Now back to the insulation; the 2.6-inch insulation should be installed as close to the extension ring as possible, chamfered as required to fit under the flange. Next the tapered insulation sump is installed. This should be installed as close as possible to the extension ring flange and chamfered as required to fit beneath the flange. All voids between the extension ring and the insulation should be filled with spray polyurethane foam insulation.

Once we have our insulation installed, next comes the cover board. The number one thing with the cover board and roof drain is having the cover board cut perpendicularly to the roof drain flange. (See Photo 2.) Do notchamfer the cover board. Chamfering the cover board may ease the transition of the membrane onto the extension ring flange, but it creates an unsuitable substrate surface for the bonding adhesive. And in my experience, water seems to end up ponding around the roof drain and not dropping into the roof drain. This will also allow the roof’s drain clamping ring to sit flat and below the roof surface of the roof.

Photo 3. The membrane has been correctly cut in a cloverleaf pattern. Photos: Hutchinson Design Group Ltd.

Now that our cover board is installed, we have the membrane and its transition into the roof drain. Water cut-off mastic is to be installed on the extension ring flange. How much you ask? One tube. Load that flange up. Make two thick beads with it. I have never heard a contractor say, “Man, using all of that water cut-off mastic on the job really set me back.” It’s a small item, but it is worth it.

After the membrane has been installed and the clamping ring is set, it’s time to cut a hole in the membrane to allow the water to get to the drain and off the roof. How big should the hole be? As small as possible is what some contractors might say. I ask a question to you now: what is the goal of the roof drain? If you answered to get the water off the roof as quickly as possible, you would be correct. Then why would the contractor want to cut a small hole in the roof membrane that would restrict the flow of water into the roof drain piping and off of the roof? I am dumbfounded as well. When we detail the roof drain, we call for the membrane to be cut back to within a 1/2 inch of the extension ring in a cloverleaf pattern around the clamping ring bolts. (See Photo 3.) This way there is no confusion on how far back the membrane is to be cut. Set the drain dome and the roof drain detail is complete.

So, there you have it. Now the roof can drain properly with a brand-new roof drain with no problem (fingers crossed).

Retrofit Roof Drains Feature Integrated Vortex Breaker

OMG Hercules-Plus RetroDrainsOMG Roofing Products introduces a new line of retrofit roof drains called Hercules-Plus. The drains feature integrated vortex breaker technology. Vortex breaker technology helps improve drain performance by improving water removal off the roof.

According to the manufacturer, independent performance testing shows that Hercules-Plus RetroDrains provide up to 2.5 times greater flow capacity than original Hercules Drains without vortex breaker technology. Faster water flow off the roof also means that the drains get excessive weight off the roof faster. In addition, integrated vortex breaker technology greatly reduces the chugging effect that occurs when a vortex collapses, which can overload the plumbing system.

“Ponding water weighs approximately five pounds per inch per square foot. That means one-inch of water covering 20-square feet on the roof weighs 2,000 pounds,” said Dan Genovese, product manager with OMG Roofing. “That’s an additional ton of live load added to the building’s roof, and not entirely uncommon given the number of extreme weather events we’ve seen in the past few years. The new Hercules-Plus RetroDrains can get that water – and excessive weight – off the roof faster.”

Hercules-Plus RetroDrains are available in four sizes: 3 inches, 4 inches, 5 inches and 6 inches, and with an optional TPO or PVC coated flange for direct membrane attachment. Strainer domes are made of heavy-duty cast aluminum which will not rust for long life on the roof. In addition, the safety yellow powder coat makes the Hercules-Plus strainer domes highly visible to help minimize rooftop trip hazards.

For additional information, visit www.OMGRoofing.com.

Vortex Breaker Strainer Dome Improves Drain Performance

OMG Roofing Products introduces the Vortex Breaker Strainer Dome

OMG Roofing Products introduces the Vortex Breaker Strainer Dome for retrofitting OMG Hercules Drains. The new strainer dome with built-in vortex breaker technology is designed to improve water flow from the roof. According to the manufacturer, independent studies demonstrate that when upgraded with the Vortex Breaker Strainer Dome, Hercules Drains offer up to 2.5 times greater flow capacity than Hercules Drains without vortex breaker technology. Faster water flow off the roof also means that the drains get excessive weight off the roof faster. In addition, the integrated vortex breaker technology greatly reduces the chugging effect that occurs when a vortex collapses, which can overload the plumbing system.

Vortex Breaker Strainer Domes are made of heavy-duty cast aluminum for long life on the roof. The safety yellow powder coat makes them easily visible on the roof, so they do not pose a trip hazard. The new domes are compatible with all 3-, 4-, 5- and 6-inch OMG Hercules and OMG Aluminum Classic drains, including thermoplastic coated versions, and are installed using only a screwdriver with a #2 square drive.

For additional information, please call the Customer Service team at OMG Roofing Products at (800) 633-3800.

After Years of Roof Leaks, a Laboratory That Produces Theatrical Equipment and Software Undergoes a Complex Reroofing

Founded in 1910, Rosco Laboratories is a multi-national producer of equipment, software and products for the theatrical, film, and television industries and architectural environment. As with every aging flat roofing system, water leakage was becoming a recurring problem at Rosco’s Stamford, Conn., facility. The severity of the leakage was further exacerbated by the lack of roof drainage (only two roof drains serviced the entire building) and poor deck slope conditions (less than 1/16 inch per foot).

The gypsum decking was cut out within the limits of the entire framing “bay” and infilled with galvanized metal decking. The longitudinal deck panel edge was seated atop the horizontal leg of the bulb-tee section (visible in the center of the photograph) and mechanically fastened using self-tapping screws. The ends were supported by the steel purlins. The underside of the decking was prepainted to match the ceiling finish. Supplemental structural support consisting of strips of 14-gauge galvanized sheet metal were attached to the bottom of each bulb-tee section contiguous to the repair to provide additional support for the adjacent gypsum roof decking segment.

The gypsum decking was cut out within the limits of the entire framing “bay” and infilled with galvanized metal decking. The longitudinal deck panel edge was seated atop the horizontal leg of the bulb-tee section (visible in the center of the photograph) and mechanically fastened using self-tapping screws. The ends were supported by the steel purlins. The underside of the decking was prepainted to match the ceiling finish. Supplemental structural support consisting of strips of 14-gauge galvanized sheet metal were attached to the bottom of each bulb-tee section contiguous to the repair to provide additional support for the adjacent gypsum roof decking segment.


Rosco representatives employed traditional methods to control and/or collect the moisture within the building by use of several water diverters. This technique was effective but Rosco representatives soon recognized this was not a viable long term solution as the physical integrity of the roof structure (deck) became a principal concern to the safety of the building occupants.

The Fisher Group LLC, an Oxford, Conn.-based building envelope consulting firm was retained by Rosco in March 2009 to survey the existing site conditions and determine the need for roofing replacement. The existing roofing construction, which consisted of a conventional two-ply, smooth-surfaced BUR with aluminized coating, exhibited numerous deficiencies (most notably severe alligatoring) and was deemed unserviceable. Construction documents, including drawings and specifications and a project phasing plan were developed by Fisher Group to address the planned roof replacement.

Bid proposals were solicited from prequalified contractors in June 2010, and F.J. Dahill Co. Inc., New Haven, Conn., was awarded the contract on the basis of lowest bid.

Existing Conditions

The building basically consists of a 1-story steel-framed structure constructed in the 1970s. It is a simple “box”-style configuration, which is conducive to manufacturing.

In conjunction with design services, destructive test cuts were made by Fisher Group in several roof sections as necessary to verify the existing roofing composition, insulation substrate, moisture entrapment, and substrate/deck construction. A total of four distinct “layers” of roofing were encountered at each test cut. The existing roofing construction consisted of alternating layers of smooth- and gravel-surfaced, multi-ply felt and bitumen built-up roofing. The bitumen contained throughout the construction was fortunately asphalt-based. Succeeding layers of roofing were spot mopped or fully mopped to the preceding layer (system). The combined weight of the roofing construction was estimated to be upwards of 20 to 22 pounds per square foot when considering the moisture content. This is excessive weight.

The roof insulation panels were set into ribbons of low-rise polyurethane foam insulation adhesive. The adhesive was applied in a continuous serpentine bead, spaced 6 inches on-center throughout the field of the roof.

The roof insulation panels were set into ribbons of low-rise polyurethane foam insulation adhesive. The adhesive was applied in a continuous serpentine bead, spaced 6 inches on-center throughout the field of the roof.


It is interesting to note that a minimal amount of roof insulation was present in the existing construction. Insulation was limited to a single layer of 1/2-inch-thick fiberboard. Additional insulation would need to be provided as part of the replacement roofing construction to increase the roof’s thermal performance and comply with the prescriptive requirements of the Connecticut State Energy Conservation Construction Code.

The structural substrate, or decking, is conventional in nature, comprised of poured gypsum roof decking. The roof decking incorporates 1/2-inch gypsum formboard loose laid between steel bulb-tee supports spaced about 32 inches on-center. The poured gypsum roof decking in this instance was utilized as the structural substrate and for insulating purposes. Poured gypsum roof decking has a minimal insulating value of perhaps R-2 to R-3, which is obviously considered to be minimal by present standards.

A representative number of bulk material samples were obtained by Fisher Group from the existing roofing construction as necessary to determine the material composition. The sampling included field membrane roofing plies, coatings and cements, and associated roof penetration and perimeter flashings. Laboratory analysis revealed that the second, third and, in some instances, fourth roofing “layers” (field membrane plies) contained varying amounts—5 to 10 percent—of asbestos (chrysotile) which would necessitate full abatement of the roofing construction.

PHOTOS: The Fisher Group LLC

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Concise Details and Coordination between Trades Will Lead to a Quality Long-term Solution for Roof Drains

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

The 2015 IECC roof thermal insulation codes have forced roof system designers to actually think through the roof system design rather than rely on generic manufacturers’ details or the old built-up roof detail that has been used in the office. Don’t laugh! I see it all the time. For the purpose of this article, I will deal with new construction so I can address the coordination of the interrelated disciplines: plumbing, steel and roof design. In roofing removal and replacement projects, the process and design elements would be similar but the existing roof deck and structural framing would be in place. The existing roof drain would need to be evaluated as to whether it could remain or needs to be replaced. My firm typically replaces 85 percent of all old roof drains for a variety of reasons.

The new 2015 IECC has made two distinctive changes to the 2012 IECC in regard to the thermal insulation requirements for low-slope roofs with the continuous insulation on the exterior side of the roof deck:

  • 1. It increased the minimum requirement of thermal R-value in each of the ASHRAE regions.
  • 2. It now requires that this minimum R-value be attained within 4 feet of the roof drain.

Item two is the game changer. If you consider that with tapered insulation you now need to meet the minimum near the drain, as opposed to an aver- age, the total insulation thickness can increase substantially.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

THE ROOF DRAIN CHALLENGE

The challenge I see for designers is how to properly achieve a roof system design that will accommodate the new insulation thicknesses (without holding the drain off the roof deck, which I believe is below the designer’s standard of care), transition the roof membrane into the drain and coordinate with the related disciplines.

For the purpose of this tutorial, let’s make the following assumptions:

  • Steel roof deck, level, no slope
  • Internal roof drains
  • Vapor/air retarder required, placed on sheathing
  • Base layer and tapered insulation will be required
  • Cover board
  • Fully adhered 60-mil EPDM
  • ASHRAE Zone 5: Chicago area

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

Once the roof drain locations have been selected (for those new to this, the roof system designer should select the roof drain locations to best suit the tapered insulation layout), one should try to locate the roof drain in linear alignment to reduce tapered insulation offsets. The drain outlets should be of good size, 4-inch minimum, even if the plumbing engineer says they can be smaller. Don’t place them hundreds of feet apart. Once the roof drain location is selected, inform the plumbing and structural engineers.

STRUCTURAL ENGINEER COORDINATION
The first order of business would be to give the structural engineer a call and tell him the plumbing engineer will specify the roof drain sump pan and that the structural engineer should not specify an archaic, out-of-date sump pan for built-up roofs incorporating minimal insulation.

When located in the field of the roof, the roof drains should be at structural mid spans, not at columns. When a structural roof slope is used and sloped to an exterior roof edge, the roof drains should be located as close to walls as possible. Do not locate drains sever- al or more feet off the roof edge; it is just too difficult to back slope to them. Inform the structural engineer that the steel angles used to frame the opening need to be coped to the structure, not laid atop the structure. There’s no need to raise the roof deck right where all the water is to drain.

FIGURE 2: A threaded roof drain extension is required to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

FIGURE 2: A threaded roof drain extension is required
to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

PLUMBING COORDINATION
Now call the plumbing engineer and tell him you need a metal sump receiver (see Photo 1), underdeck clamp (see Photo 2), cast-iron roof drain with reversible collar, threaded extension ring capable of expanding upward 5 inches, and cast-iron roof drain clamping ring and dome.

Send the structural and plumbing engineer your schematic roof drain detail so they know exactly what you are thinking. Then suggest they place your detail on their drawings. Why? Because you cannot believe how much the plumbing roof-related details and architectural roof details often differ! Because details differ, the trade that works on the project first—plumbing— leaves the roofing contractor to deal with any inconsistencies.

Your detail at this point should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck (see Figure 1).

PHOTOS AND ILLUSTRATIONS: HUTCHINSON DESIGN GROUP LLC

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From Green to Blue: Making Roof Systems Sustainable in Urban Environments

Municipal storm-water managers historically have focused on controlling runoff from ground-level impervious surfaces, such as roadways, sidewalks and parking areas. However, the next frontier in storm-water management is rooftops. In urban storm-water management, roofs are part of the problem and potential solution. An exciting new technology to control rooftop runoff is known as blue roofs. Over the next several years, New York City alone will spend several billion dollars on green infrastructure solutions to address its storm-water-control problem, and blue roofs will be a key part of these efforts.

Blue-roof trays are held in place with stone ballast and hold up to 2 inches of water. The tray systems resulted in a 45 percent reduction in roof runoff during rainfall events in a New York pilot project.

Blue-roof trays are held in place with stone ballast and hold up to 2 inches of water. The tray systems resulted in a 45 percent reduction in roof runoff during rainfall events in a New York pilot project.

Blue Roofs

The roofing industry has become very familiar with the use of vegetated, or green, roofs. The vegetative layer grown on a rooftop provides shade and removes heat from the air through evapotranspiration, ultimately reducing temperatures of the roof surface and the surrounding air. By reducing the heat-island effect, these buildings require less energy to cool in the summer and use fewer natural resources (oil or other fuel) in the process.

However, an even newer and less-well-known sustainable technology applicable to roofs is the blue roof. A blue roof temporarily stores rainwater in any of a number of types of detention systems on the roof. They are most applicable and provide the most benefit in highly urbanized cities that are serviced by combined sewers. Combined sewers handle sewage and rainwater runoff from roofs, streets and other impervious surfaces. On dry days, these combined sewers can easily handle the amount of sewage flowing through them to the local treatment plant. However, on days with heavy rain, these combined systems can easily overflow with rainwater and raw, untreated sewage. This combined sewer overflow, or CSO, can flow into local sensitive receptors, like streams, ponds and oceans, contaminating the natural resources and killing fish and other wildlife dependent on them.

The beauty of blue roofs is they can store much of this rainwater during and immediately after a rainstorm, temporarily preventing it from reaching the sewer system. In this way, CSOs are minimized and local natural resources are protected. When the storm is over and the sewer system has the capacity to handle it, the blue-roof retention materials are designed to slowly release the stored rainwater back into the storm-drain system.

This blue roof in New York uses a check dam to retain storm water.

This blue roof in New York uses a check dam to retain storm water.

NYC Pilot Program

Our firm, Geosyntec Consultants, along with environmental engineers Hazen and Sawyer and HydroQual and water-management firm Biohabitats, designed and implemented a groundbreaking blue-roof system in New York. The New York City Department of Environmental Protection (NYCDEP) retained the team to implement a sustainable green infrastructure retrofit pilot program to demonstrate how rooftops can reduce the frequency and volume of CSOs in the city. The objective was to design and install storm-water controls to quantify the benefits of sustainable approaches as a viable solution to reduce storm-water flows to the city’s CSO system. Rainfall of less than 1/2 inch can overload the system and result in untreated discharges. The use of sustainable green infrastructure, like blue roofs, to reduce storm-water inputs to the combined system is one of many approaches New York City is considering to help solve this problem.

Geosyntec’s role on the team was to design several storm-water pilot studies, including blue roofs. Our blue-roof designs included installing risers on rooftop outlets that would result in ponding of water around the outlets, small dams on the roof surface using check dams of angle-iron to create ponding and the most successful technique—blue-roof trays. We developed specially designed trays, held in-place with stone ballast, to hold up to 2 inches of water. The tray systems resulted in a 45 percent reduction in roof runoff during rainfall events. If blue-roof trays were installed on all roofs in an entire drainage area to a CSO, the results would be significant in solving the CSO problem. In addition, trays are more practical because they can be spaced around existing equipment on roofs and moved during repairs and maintenance of other rooftop systems.

Geosyntec Consultants designed a blue roof that included installing risers on rooftop outlets that would result in ponding of water around the outlets.

Geosyntec Consultants designed a blue roof
that included installing risers on rooftop outlets that would result in ponding of water around the outlets.

Roof-system Protection

Protecting the integrity of a roof membrane is an important consideration for roofing and building contractors that are considering installing a blue roof. Blue-roof-tray systems offer the best protection because they rest on top of existing membranes and ballast systems and do not result in any membrane perforations that require additional waterproofing. Other blue-roof systems, like check dams or new drain inserts, may require additional waterproofing. The bottom line is if the roof membrane is old, compromised or currently leaking, any type of blue roof would be problematic until a new membrane is installed.

In addition, during the pilot projects, we took great care to inspect and test the roofs for load-bearing support—a step that should be conducted for all blue and green roof systems.

As we look to the future, roofs in urban areas will most definitely become a major part of the storm-water solution, and blue-roof technologies will evolve to become a common practice.

Learn More

NYCDEP has posted information about blue roofs and other urban green infrastructure for CSO control on its website.
The U.S. Green Building Council offers an online course about blue roofs for storm-water management.

PHOTOS: Geosyntec Consultants