PLUMBING DESIGN by the NUMBERSBy James E. Stenqvist, CPD Storm Drainage Components A building’s storm drainage components consist of numerous styles of roof drains, overflow drains, roof receptors, promenade drains, parking area drains, planter drains, siphonic drains, downspout nozzles, downspout boots, and scupper drains. Knowing the architectural intent of the roof design and type of roof ensures that the correct components are specified. Typical types of roof installations are concrete roof decks without insulation, thick concrete roof decks with insulation, steel deck with insulated built-up roof, precast concrete deck, and above-grade concrete deck (see Figure 1). Working with the structural engineer to tackle the secondary drainage requirements helps determine if scuppers, overflow drains, or spilling over the roof edge to provide a second means of roof drainage in the event of the primary system being clogged is necessary. A roof drain consists of three basic parts: the strainer, the flashing ring with gravel stop, and the drain body. The strainer materials vary. Personally, I dislike the use of PVC as a strainer material because I’ve surveyed too many roofs where PVC strainers are missing, cracked, or damaged. Once the strainer is gone, the storm piping is susceptible to clogging, which can lead to roof failure. Figure 2 Typical main roof drain Figure 3 Flow control roof drain Storm Drainage Components A typical main roof drain (see Figure 2) is usually 3–6 inches outlet diameter, and high-capacity drains are typically 8–12 inches outlet diameter. The large open area dome permits an unobstructed flow. The outlet type can be caulk, threaded, or no-hub. Specify a drain sump to prevent the intrusion of debris, adjustable extension, and a locking mechanism to secure the dome. When using a flow control roof drain (see Figure 3), specify a minimum of two drains. Limit the roof area to 25,000 square feet per weir opening. There should be a 50-foot maximum distance from the edge of the roof to the drain, a 50-foot maximum distance from the end of the valley to the drain (for sloped roofs), and a 200foot maximum distance between drains. Factor in wind effect when locating the drains and determining the number. A gutter or cornice roof drain (see Figure 4) is a roof drain for installation in gutters, cornices, balconies, and other overhanging construction to prevent overflow to areas below. Its flat strainer does not obstruct traffic. It can have a low dome to intercept debris in gutters and valleys or a high dome when high levels of debris are present. These drains are available with bottom, side, or 45-degree outlets. An overflow drain (see Figure 5) should be specified to prevent the overloading of roofs where the building code calls for a specific maximum water buildup depth. Overflow drains should drain separately from the primary system. Discharge shall Figure 4 Gutter or cornice roof drain Figure 1 Types of roof installation Any Insulated Deck Promenade Finished Deck Figure 5 Overflow drain Poured Concrete Precast Deck 40 Plumbing Systems & Design NOVEMBER/DECEMBER 2006 PSDMAGAZINE.ORG or nickel bronze grates for pedestrian. Typically. This article is meant to provide some basic guidelines. The body and flange are cast bronze. and roofs with decks for recreational purposes. A siphonic roof drain (see Figure 8) should be tested and certified in accordance with ANSI/ASTM A112. The clamping arrangement ensures watertight assembly. The nozzle design diverts water away from the building. Outlet configurations are side and bottom outlet. roof receptors are cast iron. Specify a roof receptor (see Figure 6) for indirect waste. A downspout boot (see Figure 12) is used as a transition piece for connecting a sheet metal. eliminating wall stains. Smith Manufacturing Company. 5 by 4 inches. NOVEMBER/DECEMBER 2006 Plumbing Systems & Design 41 . e-mail articles@psdmagazine. Always check all relevant codes and resources for a particular project. For more information or to comment on this article. An area drain (see Figure 7) is used for flat parking areas. Its sturdy cast iron construction protects the lower part of the exposed downspout from damage. Conn. available in 4-inch diameter outlets.6. A parapet roof drain (see Figure 9) serves as a scupper drain allowing drainage through parapet walls. The piping system is designed to operate with the piping completely filled during a rainstorm. Figure 9 Parapet roof drain Figure 11 Downspout nozzle be above grade.org. The wall flange covers the rough opening and serves as an anchor. The 2½-inch-high solid water dam prevents normal rainwater from entering the waste line.Figure 6 Roof receptor Siphonic Roof Drains. The body material can be galvanized or cast iron. Area drains are available with cast iron bodies with cast iron.9: Figure 7 Area drain Figure 12 Downspout boot The body material can be galvanized or cast iron. and the discharge location shall be where normally observed. cooling towers. available in 2-inch through 6-inch diameter outlets. Scupper drains (see Figure 10) are used at specific angles at the junction of the roof and parapet with connection to an outside conductor. An air baffle prevents air from entering the piping system at peak flow. CPD. …continued on page 43 Figure 8 Siphonic roof drain A downspout nozzle (see Figure 11) is used as a parapet overflow or at the base of a wall where a concealed leader discharges rainwater to the ground. vehicular. and other mechanical devices (check with local codes as these wastes may need to discharge to sanitary). is a project engineer with Diversified Technology Consultants in North Haven. Typical sizes are 4 by 3 inches. Figure 10 Scupper drain to underground cast iron soil piping. ductile iron. exposed downspout James Stenqvist. A convex grate allows ample drainage area if the sides become clogged with debris. and 4 inches square. or heavy vehicular traffic. Ackowledgement All photos in this article were supplied by Jay R. Roof receptors are used to receive wastewater from air conditioning units. exterior courtyards. with bottom outlets in 2-inch to 6-inch diameters. The sleeve may be flashed at the parapet wall and is held firmly in place by the adjustable wall flange.