Rainfall rate inches per hour.
How to figureout number roof drain for a flat roof.
1 calculate the roof area to be drained.
Calculate the total roof area by multiplying its length by width.
Size downspouts to fit the gutter.
5 19 6 sq in.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
2 estimate the roof drain outlet size you will likely use.
Ipc provides four steps to size the roof drains on a building.
It affects walkability as well as drainage and roofs in areas of high rain or snowfall tend to have steeper pitches.
6 inch hr.
3 inch hr.
Flat roof drainage capacity of a single drain pipe or leader.
Pipe cross section drainage area.
4 roof drain 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.
How to calculate the quantity of drains required.
Select number of roof drains and calculate the roof area sloped to each drain.
Calculate total roof area.
Conversely the larger the drain outlet diameter the fewer you will need.
The more drains you will need.
The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.
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.
Roof pitch affects the actual area of the roof.
Size horizontal storm drainage piping.
Using tools from the international plumbing code ipc it s not that hard.
Size and placement of rooftop equipment may necessitate additional roof drains.
It is important to remember that no roof area should ever have less than two roof drains.
Next the roof area is divided by the area for each leader to determine the number of drains required.
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.
Determine 100 year 1 hour rainfall rate used for location of building.
2 inch hr.
1 inch hr.
Determine leader or pipe size.
The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout.
This information can be obtained from the pipe or drain manufacturer.
Roof area is 200 x 500 100 000 sq.
4 inch hr.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.