18 • IIBEC Interface July 2022 Proper detailing of roof penetrations is a vital part of every completed roofing assembly. Any penetrations through a low-slope roof assembly could represent potential failure points and leaks during the life cycle of the roof. Whether the project is new construction or reroofing, the roof manufacturers and design professionals develop very specific detailing procedures to reduce the possibility of breaches occurring. The roofing professionals who undertake the project must be capable of meeting the expectations of the owner, the manufacturer, and the design team. The roofing installation crew should be well trained and experienced in the roof manufacturer’s recommended installation techniques as well as the architect’s and building enclosure consultant’s design details. As mentioned in the first article of this series, the intent of this series of articles is not to explain design requirements but rather to provide a “roofing 101” narrative on best practices. To that end, this article describes selected issues related to detailing roof penetrations and the technical aspects of flashing related to drainage in the thermoplastic roof system; the article is not intended to provide technical specifications for design issues such as proper sizing, waterflow, head of water, or drain locations. ROOF DRAINS Roof drains and overflow drains are among the most critical components of any internally drained roof assembly because they are responsible for the removal of water from the roof system. As part of that system, the primary and overflow drains perform independently from each other. The primary drain is generally located at a low point of the roof area and is in plane with or set lower than the roof membrane plane so as to collect the vast majority of water. The overflow drains are generally set slightly above the roof plane as required by local rainfall records, building codes, and environmental requirements. Insulation drain sumps involve additional considerations. The tapered sump should have a four-sided, gradual slope (Fig. 1), and the tapered insulation within the drain sump should not reduce the minimum R-value thickness of the roof insulation by more than 1 in. (25 mm). For instance, Section 402.2.1.2 of the 2021 International Energy Conservation Code1 indicates that “the minimum thickness of above-deck roof insulation at its lowest point, gutter edge, roof drain or scupper, shall not be less than 1 in. (25 mm).” Figures 2 and 3 illustrate incorrect tapering and flashing of the drain sump. In these examples of incorrect tapering and flashing, there are several issues: • The slope is greater than 2 in 12. However, there should not be any vertical transitions. Instead, the sump should have gradual slope on all four sides. • There are field membrane splices closer than 9 in. (229 mm) to the drain clamping ring. Field splices are generally not permitted to be within 12 in. (305 mm) of the clamping ring per the roof manufacturer specifications; manufacturers may have slightly different criteria for Figure 1. Diagram of a four-sided tapered drain sump. July 2022 IIBEC Interface • 19 this item. The force exerted on the roof membrane from installing the drain clamping ring can pull tension on adjacent field seams, which could weaken or damage the field splice. The tension could cause wrinkles and voids in adjacent field seams if they are in close proximity to the drain assembly. • The vertical surfaces of the “sump” area are bare/exposed polyisocyanurate (polyiso) insulation, which means there is no insulation facer to adhere to, resulting in loose flashing and, potentially, damage to the polyiso insulation from solvents in the bonding adhesive. • A metal drain pan is installed, which is not required by code and not recommended by the roof manufacturer, above the roof insulation (Fig. 3). The metal drain pan, if specified, should be installed against the structural deck, not on top of the insulation assembly. A sump pan (or sump receiver) is a square, approximately ⅛-in.- (3-mm-) thick, flat piece of steel (unless it is a dual pan). It should fit the roof drain bowl, and its purpose is to assist in securing the drain bowl to the roof deck. Sump pans are manufacturer specific, so they cannot be interchanged with other manufacturers’ roof drains. Metal drain pans are not typically installed in conjunction with single-ply roof systems in many areas of US but can be incorporated by the designer. • The inside corner detailing at the vertical transitions is not installed per the manufacturers’ specifications, and the roof contractor has not installed the manufacturer-required unreinforced thermoplastic flashing detail membrane. • There are no inside or outside corner detail flashings installed in this example. • The primary roof drain and the overflow drain are installed at the same elevation. The completed overflow drain clamping ring did not include an overflow drain collar adapter. The overflow drain will function the same as a primary drain, channeling water into the overflow drain outlets at all times. Overflow drains are intended to actively remove water in the event the primary drain becomes clogged. As the overflow drain begins to remove water from the roof, it generally discharges (also known as daylights) onto the grounds of the facility, thereby providing a visual indication that the primary drain is not functioning properly. The overflow drain lines are generally not connected to the plumbing system. • Additionally, for this particular project, the insulation system is specified to be adhered with foam adhesive and is intended to receive a hail coverage rider with the warranty. The use of insulation fastening plates is generally prohibited by the roof manufacturer on projects where a hail coverage warranty is specified because the metal attachment plates introduce a very hard pinch point for the roof membrane at hail impact points. • The insulation is cupped and loose, and the fasteners and insulation plates that have been installed to compensate for inadequately adhered insulation introduce thermal bridging to the roof assembly. Because the metal fasteners and plates are secured into the metal deck, they will easily transmit temperature differences between the Figure 2. This photo illustrates incorrect flashing of a drain sump with thermoplastic roof membrane. Figure 3. Photo showing an incorrect drain sump configuration, improper installation of a metal drain pan, and foreign material adhered to drain pan. 20 • IIBEC Interface July 2022 interior and exterior, resulting in thermal bridging and thermal loss. • The fasteners are also penetrating the underlying vapor barrier, which was designed in this assembly to not be penetrated by fasteners because it is installed over the mechanically attached substrate board. DRAIN FLASHINGS Drain flashing should be accomplished as shown in Fig. 4. Butyl-based mastic must be present between the drain bowl flange and the underside of the roof membrane (see notation A in Fig. 4). The mastic should be visible, oozing out slightly from under the roof membrane inside the drain bowl and clamping ring. There should also be a discernable hump of mastic under the roof membrane adjacent to the exterior edge of the clamping ring. Lead or metal drain pans are not recommended and should not be used with thermoplastic membrane systems above the insulation board as shown in this case. All bolts with washers (see notation B in Fig. 4), as required by roof manufacturer specifications and The NRCA Roofing Manual: Membrane Roof Systems,2 must be in place and must be tight enough to provide compression of the clamping ring against the butyl mastic, which ensures a long-term water-tight seal. Every fastener location on the clamping ring and threaded hole in the drain bowl must receive a new stainless steel bolt. Stainless steel is recommended because it is less likely to corrode. Much like a wheel on a vehicle, every fastener location must receive a fastener to provide even pressure. A simple test to check the tightness of the drain bolts is to try to spin the washers: if the washer spins, the bolt is not tight. The bolt assembly clamping ring must be secured into the drain bowl. It is important to ensure that there is no damage to the bolts, threads, or washers and no cracks in the clamping ring, bolts, or washers. All bolt holes in the drain clamping ring must receive a bolt. In reroofing scenarios, it is recommended that existing bolts be replaced with new bolts. It is also recommended that the new bolts and washers are stainless steel to provide long-term performance. On any roofing or reroofing project, the roofing team should ensure that the drain ring is not cracked or broken in any way. The clamping ring must be intact to provide constant compression against the butyl mastic. Damaged clamping rings must be replaced. (You may have noticed that I have reiterated this issue a few times. It has been my experience over the years that there will be situations where someone has attempted to reuse a cracked clamping ring on reroofing projects and leaks occur.) The drain basket should also be intact and secured in place into the clamping ring. This is vital to prevent debris from flowing into the drain and creating a backup or clog. Backups and clogged drains could cause structural overloading of the roof structure during heavy or prolonged rain events. The thermoplastic roof membrane must extend at least ½ in. (13 mm) toward the middle of the bowl past the bolt protrusions of the clamping ring (see notation Figure 4. Example of a roof detail sheet. Figure 5. Standard scupper detail with thermoplastic olefin/polyvinyl chloride–coated metal scupper sleeve. C in Fig. 4). In other words, the roof membrane must be visible inside of the clamping ring. It is important to ensure that the drainage hole cut in the membrane is larger than the drainpipe but smaller than the clamping ring bolt protrusions. There should be no cuts or slices into the membrane that extend back toward or under the bolts and clamping ring. Such cuts could expand and create moisture intrusion issues behind the clamping ring. If such cuts are present, the clamping ring should be removed, the roof membrane around the outside of the drain bowl cut away, and a target patch of new roof membrane installed per the roof manufacturers’ specifications. The manufacturers specify that such target patches be of sufficient size to ensure the heat-welded seam edges will be located a minimum of 12 in. (300 mm) from the roof drain and overflow drain clamping rings. Then the butyl mastic and clamping ring should be reinstalled as described previously. Field splices must not run though the drain ring or the drain sump, or within 12 in. (305 mm) of the compression ring because the membrane tension caused by tightening the compression ring can distort or wrinkle the field splices. (See notation D in Fig. 4; also, please note that 12 in. [305 mm] is a typical distance; for the project-specific distance, see the roof manufacturers’ specifications.) If field seams or splices should occur within the tolerance area, cut the membrane back and install a target patch as described previously. The overflow drain collar/dam should be at a higher elevation than the primary roof drain in accordance with local requirements (notation E in Fig. 4). The height of the overflow collar/dam must meet the requirements established by the roof drainage calculations for head of water for the geographic location of the project. During construction, reroofing, or roofing operations, a temporary strainer cover, as indicated by notation F in Fig. 4., should be in place to prevent debris from entering the drainpipes. ROOF SCUPPERS Another very important detail for directing waterflow from the roof is the scupper and overflow scupper. Figure 5 is a typical scupper detail drawing from a roof manufacturer. July 2022 IIBEC Interface • 21 IIBEC half page.indd 1 4/18/2022 4:07:54 PM Figure 6. Incorrect scupper fabrication (no flange attached). 22 • IIBEC Interface July 2022 When using a metal scupper flange insert, whether it is coated metal, bare metal (such as galvanized or stainless steel), or prefinished metal, the following items must be incorporated: • The horizontal metal deck flange of the scupper must be supported by wood blocking to prevent the metal flange from buckling or bowing when fastened. Figure 6 shows a scupper without flanges, which does not meet the roof manufacturers’ detailing and specification requirements. • The wood blocking should be wider than the metal flange to ensure that the blocking fully supports the metal flange. • Most roof manufacturers require a butyl-based mastic sealant installed between the back side of the metal scupper flange and the membrane wall flashing around the scupper opening to provide a sealed gasket—much like the seal achieved at roof drain compression rings. • The fasteners securing the scupper should be installed through the bead of the butyl mastic to provide compression against the butyl mastic and help seal the fastener penetrations. • When using coated metal, the flashing process is simplified because the flashing membrane can be hot-air welded to the scupper. • If using bare or prefinished metal, primed and self-adhered flashings will be required. Roof manufacturers’ requirements can differ slightly: whereas some manufacturers require selfadhered thermoplastic flashing to be used to strip in the scupper flanges, other manufacturers allow the use of a hybrid flashing detail using self-adhered ethylene propylene diene terpolymer (EPDM) flashings to strip in the scupper flanges on a thermoplastic olefin membrane system (Fig. 7). • Inside the scupper opening, once the membrane flashings have been installed, most roof manufacturers will require inside corner detailing. Refer to the individual manufacturer’s requirements pertaining to warranty coverage limits for field-fabricated corner details versus premolded corner details. • Overflow scuppers, much like overflow drains, should be installed at a higher elevation on the wall based on drainage calculation for the specific project so that they only collect and direct water off the roof when the primary scupper has malfunctioned or become clogged. GUTTER AND DOWNSPOUT SYSTEMS Gutter systems and downspouts are another type of high-flow water management system incorporated into some thermoplastic roof systems. Figure 8 shows a typical gutter detail installation. Key considerations for these systems include the following: • The gutter and downspouts must be sized, spaced, and formed to meet the drainage calculations. The gutter should be designed such that it captures the water as it flows over the metal edge flashing without overshooting the exterior edge of the gutter. Figure 8. Typical gutter edge detail. Figure 7. Hybrid scupper flashing with self-adhering ethylene propylene diene terpolymer (EPDM) white flashing over a thermoplastic roof system. July 2022 IIBEC Interface • 23 • There must be wood blocking in place. This blocking must be secured per the requirements of the manufacturer, local code, FM Global,3 and the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA),4 and it must be wide enough to support the entire width of the horizontal deck flange of the metal edge or gutter. • The roof membrane will typically be extended out and over the face of the wood blocking and be fastened into the wood blocking per the roof manufacturer’s requirements. The metal gutter and metal fascia are then secured into the wood blocking in accordance with the manufacturer, local code, FM Global, and SMACNA requirements. • The gutter should be sloped to drain toward the downspouts. • Expansion joints must be installed at the prescribed intervals based on the gutter size and length as well as specific building use and design requirements. • Gutter connections, overlaps, corners, downspout connections, and expansion joints must be sealed to be watertight. • Gutter straps and support brackets must be securely attached, sized, and spaced to be capable of supporting the gutter under load. • Downspouts must be sized, spaced, and secured per design criteria and specifications. REFERENCES 1. International Code Council (ICC). 2021. International Energy Conservation Code. Country Club Hills, IL: ICC. 2. National Roofing Contractors Association (NRCA). 2019. The NRCA Roofing Manual: Membrane Roof Systems. Rosemont, IL: NRCA. 3. FM Global. 2021. Roof Loads and Drainage. FM 1-54. Providence, RI: FM Global. 4. Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA). 2012. Architectural Sheet Metal Manual. Chantily, VA: SMACNA. Please address reader comments to chamaker@iibec.org, including “Letter to Editor” in the subject line, or IIBEC, IIBEC Interface Journal, 434 Fayetteville St., Suite 2400, Raleigh, NC.27601. Gary Gilmore, RRO, REWO, CIT Level I, is director of the roof consultant group Lerch Bates Building Insight, in Texas, where he is responsible for overseeing and executing roofing and building enclosure assessments, infrared scanning, design, contract document review, quality assurance observations, and field performance testing services. Gilmore has extensive experience working with owners, architects, general contractors, and trade contractors, assisting them in selecting and installing roofing and facade systems that are appropriate for their specific project needs with regard to building code and energy code requirements, building type and occupancy, and cost constraints. He has direct experience in field installation of roofing and cladding systems obtained through his early career on the contractor and manufacturer representative side of the industry. Gary Gilmore, RRO, REWO, CIT Level I S P E C I A L I N T E R E S T Photo by Marten Bjork on Unsplash Complete So that You Can Compete Want to win repeat business? Consider three key traits that contractors should exhibit to win additional jobs from clients they have previously served, writes Zulqernain “Zulq” Malik in Construction Executive. • Be on time and on budget. Complete your project on time and use newer technology to review past project information. That can help avoid “unforeseen circumstances” that, with better tools and more attentiveness, are all too predictable. • Quality trumps price. “Project performance includes the quality of the finished product, which includes your compliance record, site tidiness, and flexibility through project changes,” Malik explains. “When it comes to excelling on these metrics, you can’t leave anything up to chance.” • Don’t leave clients in the dark. “Owners are putting a large investment into these projects, which can often last for months or even years,” observes Malik. “Diplomacy and regular communication can go a long way to delivering peace of mind.” Source: constructionexec.com
