Converting this to gallons per minute per square foot gpm ft 2.
How much area per roof drain.
Divided by 10 200 sq.
The result is the number of drains needed.
An additional roof drain should be added for each 10 000 square foot area.
Sizing data for conventional drainage.
Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.
It is important to remember that no roof area should ever have less than two roof drains.
Number of roof leaders required is 10 100 000 sq.
To a depth of 1 in 1 hour.
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.
Ft therefore 10 roof drains would be required.
Each drain can handle 4 600 sq.
Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.
Take the roof s total square footage and divide by the total square footage handled by one drain.
Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage.
Equals 32 6 or 33 drains required.
1 inch of rainfall in an hour will cover 1 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.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
And then determine from the chart below how many roof drains you require.
Size and placement of rooftop equipment may necessitate additional roof drains.
Divided by the 4 600 sq.
Divide total roof area by area found in step 3 to obtain the number of drains required example.
The drains should be equally spaced and located symmetrically about the roof.
Leaders s ize m ax mu al owb eh rz n tp jc dr f open squarefeetatvariousrainfallrates pipesize area inches sq in.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet.
The drains should be placed at a maximum of 75 feet in each direction away from each other.
50 000 4 400 11 36.
But this isn t the whole story.
A minimum 4 inch vertical drain is required.
This reveals that the minimum size for the leader pipe is 5.
Or 12 drains required.
2 500 4 x 3 75 2 344 sq ft.
To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this.
Therefore the 100 000 sq.
Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.
