How Much Area Per Roof Drain

Divide total roof area by area found in step 3 to obtain the number of drains required example.

How much area per roof drain.

An additional roof drain should be added for each 10 000 square foot area. 2 500 4 x 3 75 2 344 sq ft. Equals 32 6 or 33 drains required. To a depth of 1 in 1 hour.

To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this. 1 inch of rainfall in an hour will cover 1 sq ft. Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft. Converting this to gallons per minute per square foot gpm ft 2.

Therefore the 100 000 sq. Each drain can handle 4 600 sq. Ft therefore 10 roof drains would be required. This reveals that the minimum size for the leader pipe is 5.

And then determine from the chart below how many roof drains you require. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Take the roof s total square footage and divide by the total square footage handled by one drain. But this isn t the whole story.

Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow. Or 12 drains required. The result is the number of drains needed. It is important to remember that no roof area should ever have less than two roof drains.

Size and placement of rooftop equipment may necessitate additional roof drains. A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet. 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. 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.

Number of roof leaders required is 10 100 000 sq. Leaders s ize m ax mu al owb eh rz n tp jc dr f open squarefeetatvariousrainfallrates pipesize area inches sq in. 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. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.

The drains should be placed at a maximum of 75 feet in each direction away from each other. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage. A minimum 4 inch vertical drain is required.

Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq. Sizing data for conventional drainage. Divided by 10 200 sq. The drains should be equally spaced and located symmetrically about the roof.