Roof Drain Pipe Size

Sizing a roof water drain.

Roof drain pipe size.

2 500 4 x 3 75 2 344 sq ft. Determine the size of leader to be used. 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. The result is the number of drains needed.

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. Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft. Step by step sizing of zurn drains step 1. But this isn t the whole story.

For larger roof drains the pipe may be smaller such as a 10 in. Therefore the 100 000 sq. Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq. This reveals that the minimum size for the leader pipe is 5.

Roof drain connected to a 6 in. To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this. Roof area is 300 x 500 ft. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.

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. A minimum 4 inch vertical drain is required. Or less in diameter the piping will be larger in diameter than the roof drain. Unfortunately recommendations aren t that straightforward because you also need to account for water pressure material friction and more.

Calculate total roof area. Roof drain connected to an 8 in. Following this logic it is possible that for roof drains 6 in. The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.

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. Take the roof s total square footage and divide by the total square footage handled by one drain. The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout. Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage.

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. Or 12 drains required. 50 000 4 400 11 36.