How Many Downpipes For Roof Area

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

How many downpipes for roof area.

A house in chicago has a roof whose actual drainage area is 1 000 square feet. The 6 in 12 pitch factor 1 1 multiplied by 1 000 yields an effective area of 1 100 square feet. Sizing downpipes downpipes are sized for the areas that discharge into them. How many downpipes do you need.

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. Downpipe fall fall fall fall fall roof pitch 45 figure 1 an example of a roof with a total plan area of 98 m. Using clause e1 table 5 see figure 2 at a roof pitch.

Min number of downpipes roof catchment area. Doubling the number of downspouts halves the required capacity for each. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Size downspouts to fit the gutter.

To calculate the minimum number of downpipes divide the roof catchment area by the allowable maximum catchment per downpipe. From figure 3 5 a in as nzs 3500 3 the maximum catchment per downpipe is 47m 2. The number of downpipes you need will depend on the size of your roof and your chosen style of guttering. Usually the size for the largest collection area on the roof is used to size downpipes throughout.

This is because larger roofs require bigger volumes of water to be diverted away from them during periods of rainfall.