Roof drain connected to an 8 in.
Roof drain pipe size.
Roof drain connected to a 6 in.
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.
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.
We regularly get asked about the water flow capacity of different pipe sizes and which is the best roof drain for a specific pipe size.
Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.
To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this.
Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft.
For larger roof drains the pipe may be smaller such as a 10 in.
Unfortunately recommendations aren t that straightforward because you also need to account for water pressure material friction and more.
Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.
Calculate total roof area.
Sizing a roof water drain.
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.
Determine the size of leader to be used.
A minimum 4 inch vertical drain is required.
50 000 4 400 11 36.
But this isn t the whole story.
This reveals that the minimum size for the leader pipe is 5.
Following this logic it is possible that for roof drains 6 in.
Or less in diameter the piping will be larger in diameter than the roof drain.
300 x 500 150 000 sq.
2 500 4 x 3 75 2 344 sq ft.
Roof area is 300 x 500 ft.
Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage.
The result is the number of drains needed.
Take the roof s total square footage and divide by the total square footage handled by one drain.
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.
Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.
For example a 4 in.
Step by step sizing of zurn drains step 1.
The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout.
Or 12 drains required.
