How Much Area Per Roof Drain

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

How much area per roof drain. 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. Divide total roof area by area found in step 3 to obtain the number of drains required example. The drains should be placed at a maximum of 75 feet in each direction away from each other. Sizing data for conventional drainage.

50 000 4 400 11 36. Therefore the 100 000 sq. Doubling the number of downspouts halves the required capacity for each. Ft therefore 10 roof drains would be required.

It is important to remember that no roof area should ever have less than two roof drains. To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall. Size and placement of rooftop equipment may necessitate additional roof drains.

Or 12 drains required. 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. But this isn t the whole story. Number of roof leaders required is 10 100 000 sq.

To a depth of 1 in 1 hour. This reveals that the minimum size for the leader pipe is 5. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. The result is the number of drains needed.

Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft. Leaders s ize m ax mu al owb eh rz n tp jc dr f open squarefeetatvariousrainfallrates pipesize area inches sq in. Divided by 10 200 sq. Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.

A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet. Divided by the 4 600 sq. 2 500 4 x 3 75 2 344 sq ft. An additional roof drain should be added for each 10 000 square foot area.

The drains should be equally spaced and located symmetrically about the roof. 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 minimum 4 inch vertical drain is required.

Equals 32 6 or 33 drains required. Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage. Converting this to gallons per minute per square foot gpm ft 2. Take the roof s total square footage and divide by the total square footage handled by one drain.