Specifier’s Guide
(You may click on any of the Charts below (A, B, C) and a larger image will appear).
Start by calculating the area of the roof surface to be covered by the drain, including any contributions from vertical surfaces and/or other surfaces discharging indirectly. For example, consider a project at a location where the local building code requires a 4.0 inch per hour rainfall intensity.
1. A roof drain on a single-ply membrane roof covering 9,500 square feet will receive 0.88 cubit feet per second (cfs) as determined using Chart A or by using the Rational Method.
2. With this maximum required flow, enter Chart B along the X-axis at 0.88 cfs. This chart indicates that this flow falls within the range of the Model 1005T03 and the depth of water around the drain when fully primed will be 2.5 inches referenced from the flashing ring surface.
3. Having selected Model 1005T03, enter Chart C at the listed outlet size, in this case 3 inches. Chart C indicates that the 1005T03 has a resistance coefficient of 0.16 to be used in hydraulic calculations. Also, this drain model has a maximum rated capacity of 1.40 cfs (39.6 liters per second).
4. Enter the drain resistance value (0.16) and design flow (0.88 cfs) into your hydraulic calculations and proceed with sizing your system.
5. Repeat these steps for all the included siphonic roof drains to select drain model, resistance coefficient and design flow.
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