1 inch of rainfall in an hour will cover 1 sq ft.
Roof area per roof drain.
Total roof area 500 by 200 100 000 sq.
300 x 500 150 000 sq.
Step by step sizing of zurn drains step 1.
Determine rate of rainfall for this example use 4.
Converting this to gallons per minute per square foot gpm ft 2.
Drainage design specific to location.
The above result is the number of roof drains required for the building.
Roof drainage systems need to be designed to cope with the rainfall intensities for the specific building location.
When sizing roof drains the limiting factor for the amount of water each drain will carry away is the size of leader therefore increasing leader size decreases the number of drains required.
According to the chart for 1 8 slope per 12 of pipe for 5 000 square feet of roof area with a 6 per hour of rainfall the required pipe size is 8.
The roof drain calculator below is based on the maximum amount of rainfall in inches per hour of the hypothetical worst storm in the past 100 years and which has a two percent chance of occurring in any given year.
Divide the total roof area by the area that one leader will handle.
Determine leader or pipe size.
Walls that drain onto a lower storey roof can increase the effective roof area by around 50.
Roof area is 300 x 500 ft.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Doubling the number of downspouts halves the required capacity for each.
The speed at which the rain collects at the drain.
The number of roof drains shown should be verified with local code requirements.
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.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
4 roof drain 3 determine your building s location on the above map to determine the approximate rainfall as measured in inches per hour.
There are 5 easy steps to figure out how many drains your commercial roofing project will need.
Calculate total roof area.
Calculate total roof area.
If the result is a fraction less use the next higher number.
Rainfall intensities vary throughout new zealand and are often very high.
To a depth of 1 in 1 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.
