Roof Drain Pipe Size

The first step in sizing a roof drain is to calculate the surface area of the roof that the drains will be covering as well as the average hourly rainfall rate at the building location.

Roof drain pipe size.

Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage. Unfortunately recommendations aren t that straightforward because you also need to account for water pressure material friction and more. Roof drain connected to a 6 in. The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout.

Sizing a roof water drain. Take the roof s total square footage and divide by the total square footage handled by one drain. This reveals that the minimum size for the leader pipe is 5. A minimum 4 inch vertical drain is required.

To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this. 2 500 4 x 3 75 2 344 sq ft. To size the vertical roof drain for the same parameters 5 000 square feet of room area and 6 per hour of rain consult table 1106 2 figure 3. Pipe size in inches vertical drain gpm 1 16 per foot gpm 1 8 per foot gpm per foot gpm per foot gpm 2 34 15 22 31 44 3 87 39 55 79 111 4 180 81 115 163 231 5 311 117 165 234 331 6 538 243 344 487 689 8 1 117 505 714 1 010 1 429 10 2 050 927 1 311 1 855 2 623 12 3 272 1 480 2 093 2 960 4 187 15 5 543 2 508 3 546 5 016 7 093.

Determine the size of leader to be used. But this isn t the whole story. 50 000 4 400 11 36. Or 12 drains required.

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. Roof area is 300 x 500 ft. Or less in diameter the piping will be larger in diameter than the roof drain. 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.

Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq. When sizing roof drains the limiting factor for the amount of water each drain will carry away is the size of leader therefore increasing leader size decreases the number of drains required. Step by step sizing of zurn drains step 1. The result is the number of drains needed.

Calculate total roof area. For larger roof drains the pipe may be smaller such as a 10 in. 300 x 500 150 000 sq. Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft.

Following this logic it is possible that for roof drains 6 in. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall. Roof drain connected to an 8 in. Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.