Horizontal Roof Drain Pipe Sizing

Roof drain connected to an 8 in.

Horizontal roof drain pipe sizing. Roof drain connected to a 6 in. The maximum number of drainage fixture units connected to a given size of horizontal branch or vertical soil or waste stack shall be determined using table 710 1 2. Take the roof s total square footage and divide by the total square footage handled by one drain. 50 000 4 400 11 36.

Roof drain vertical requirement for horizontal roof areas at various rainfall rates leader size hourly rainfall in inches pipe open 1 1 1 2 2 2 1 2 3 4 5 6 7 8 size area inches sq. The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. For example a 4 in. In total square footage covered per drain 23 14 2 880 1 920 1 440 1 150 960 720 575 480 410 360.

For example in the u k. To convert to an area for use in table 1108 2 do this. The roof drain or gutter or drain piping or downspout leader size diameter other size constraints e g. The minimum size of any building drain serving a water closet shall be 3 inches.

Following this logic it is possible that for roof drains 6 in. A 5 inch diameter pipe with a 1 4 inch per foot slope will carry 4 720 sq ft. Horizontal drain 5 000 sq ft. Or 12 drains required.

For larger roof drains the pipe may be smaller such as a 10 in. The result is the number of drains needed. A minimum 5 inch diameter drain on a 1 4 inch per foot slope is required. Adequate drainage is an important component of a properly installed roof so installing the correct size of drains is essential.

Or less in diameter the piping will be larger in diameter than the roof drain. Enter table 1108 2 until youfind a diameter pipe that will carry 4 688 sq ft. Designers specify compliance with bs en 12056 3 2000 that includes a calculation for the allowable capacity of the rainwater pipes. Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.

This means that because our horizontal pipe from step 3 was 8 our vertical pipe will be also 8. 5 000 4 x 3 75 4 688 sq ft.