How To Figureout Number Roof Drain For A Flat Roof

Rainfall rate inches per hour.

How to figureout number roof drain for a flat roof.

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. There are 5 easy steps to figure out how many drains your commercial roofing project will need. 2 inch hr. 1 calculate the roof area to be drained.

Size and placement of rooftop equipment may necessitate additional roof drains. Calculate the total roof area by multiplying its length by width. Conversely the larger the drain outlet diameter the fewer you will need. Next the roof area is divided by the area for each leader to determine the number of drains required.

1 inch hr. Determine leader or pipe size. Maximum horizontal projected roof area that can be drained in square feet. Roof pitch is a determining factor for cost of the roof as well as the roof area and the type of materials used.

Size downspouts to fit the gutter. The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. 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. Ipc provides four steps to size the roof drains on a building.

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Doubling the number of downspouts halves the required capacity for each. Select number of roof drains and calculate the roof area sloped to each drain. 5 inch hr.

Using tools from the international plumbing code ipc it s not that hard. 5 19 6 sq in. It is important to remember that no roof area should ever have less than two roof drains. 3 inch hr.

How to calculate the quantity of drains required. This information can be obtained from the pipe or drain manufacturer. 2 estimate the roof drain outlet size you will likely use. Determine 100 year 1 hour rainfall rate used for location of building.

4 roof drain 3. Roof pitch affects the actual area of the roof. Calculate total roof area. The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.

Flat roof drainage capacity of a single drain pipe or leader. Roof area is 200 x 500 100 000 sq. Size horizontal storm drainage piping. 6 inch hr.

Pipe cross section drainage area. 4 inch hr.