Roof Area Per Downpipe

The answers for downpipe size are in mm.

Roof area per downpipe.

Usually the size for the largest collection area on the roof is used to size downpipes throughout. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. The program will calculate the most suitable circular and rectangular downpipe sizes. Doubling the number of downspouts halves the required capacity for each.

The first thing you need to work out is the area of the roof that will collect rainfall which is known as the effective roof area. Roof length x half roof width x roof height 2 roof area. Select 100 x 50 rectangular downpipe. This can be calculated using the following formula.

Divide the main roof into catchments of this size and any left over area can be entered again to find a down pipe size for this smaller area. Sizing downpipes downpipes are sized for the areas that discharge into them. Using clause e1 table 5 see figure 2 at a roof pitch. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Multiplying that number by the local maximum rainfall intensity 6 8 inches per hour yields an adjusted square footage of 7 480 square feet. Determine minimum number of downpipes. Size downspouts to fit the gutter. From figure 3 5 a in as nzs 3500 3 the maximum catchment per downpipe is 47m 2.

To calculate the minimum number of downpipes divide the roof catchment area by the allowable maximum catchment per downpipe. Working out the size of your roof. Min number of downpipes roof catchment area. The 6 in 12 pitch factor 1 1 multiplied by 1 000 yields an effective area of 1 100 square feet.