A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Roof area per roof drain.
If the result is a fraction less use the next higher number.
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.
Rainfall intensities vary throughout new zealand and are often very high.
The above result is the number of roof drains required for the building.
Divide the total roof area by the area that one leader will handle.
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.
Converting this to gallons per minute per square foot gpm ft 2.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Drainage design specific to location.
Step by step sizing of zurn drains step 1.
Calculate total roof area.
Walls that drain onto a lower storey roof can increase the effective roof area by around 50.
300 x 500 150 000 sq.
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.
Total roof area 500 by 200 100 000 sq.
Doubling the number of downspouts halves the required capacity for each.
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.
The speed at which the rain collects at the drain.
Calculate total roof area.
There are 5 easy steps to figure out how many drains your commercial roofing project will need.
Roof drainage systems need to be designed to cope with the rainfall intensities for the specific building location.
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.
To a depth of 1 in 1 hour.
Roof area is 300 x 500 ft.
Determine leader or pipe size.
4 roof drain 3 determine your building s location on the above map to determine the approximate rainfall as measured in inches per hour.
1 inch of rainfall in an hour will cover 1 sq ft.
Size downspouts to fit the gutter.
