Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft.
How much area per roof drain.
2 500 4 x 3 75 2 344 sq ft.
An additional roof drain should be added for each 10 000 square foot area.
Take the roof s total square footage and divide by the total square footage handled by one drain.
Sizing data for conventional drainage.
Leaders s ize m ax mu al owb eh rz n tp jc dr f open squarefeetatvariousrainfallrates pipesize area inches sq in.
It is important to remember that no roof area should ever have less than two roof drains.
The drains should be equally spaced and located symmetrically about the roof.
Ft therefore 10 roof drains would be required.
Divided by 10 200 sq.
This reveals that the minimum size for the leader pipe is 5.
Divided by the 4 600 sq.
Therefore the 100 000 sq.
The result is the number of drains needed.
Doubling the number of downspouts halves the required capacity for each.
Converting this to gallons per minute per square foot gpm ft 2.
And then determine from the chart below how many roof drains you require.
Required roof drainage flow rate in gallons per minute 0 0104 x rainfall rate x roof area where rainfall rate is expressed in inches per hour and roof area is given in square feet.
1 inch of rainfall in an hour will cover 1 sq ft.
Each drain can handle 4 600 sq.
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.
To a depth of 1 in 1 hour.
Number of roof leaders required is 10 100 000 sq.
But this isn t the whole story.
Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Or 12 drains required.
Size and placement of rooftop equipment may necessitate additional roof drains.
Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.
When placing roof drains it is good design practice to locate the drains no more than 50 feet from the roof perimeter nor more than 100feet apart.
The drains should be placed at a maximum of 75 feet in each direction away from each other.
Divide total roof area by area found in step 3 to obtain the number of drains required example.
50 000 4 400 11 36.
Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.
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.
