How Much Area Per Roof Drain

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.

How much area per roof drain.

Equals 32 6 or 33 drains required. To a depth of 1 in 1 hour. The result is the number of drains needed. To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this.

Converting this to gallons per minute per square foot gpm ft 2. 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. Number of roof leaders required is 10 100 000 sq.

2 500 4 x 3 75 2 344 sq ft. The drains should be equally spaced and located symmetrically about the roof. The drains should be placed at a maximum of 75 feet in each direction away from each other. 50 000 4 400 11 36.

Divided by the 4 600 sq. Sizing data for conventional drainage. Area roof will require 100 000 3070 32 5 or 33 roof drains for ideal drainage. Size and placement of rooftop equipment may necessitate additional roof drains.

Or 12 drains required. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Leaders s ize m ax mu al owb eh rz n tp jc dr f open squarefeetatvariousrainfallrates pipesize area inches sq in. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.

Divided by 10 200 sq. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. 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.

But this isn t the whole story. This reveals that the minimum size for the leader pipe is 5. Take the roof s total square footage and divide by the total square footage handled by one drain. Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.

An additional roof drain should be added for each 10 000 square foot area. It is important to remember that no roof area should ever have less than two roof drains. Doubling the number of downspouts halves the required capacity for each. A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet.

Ft therefore 10 roof drains would be required. Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft. And then determine from the chart below how many roof drains you require. Divide total roof area by area found in step 3 to obtain the number of drains required example.