Roof Area Per Downpipe

To calculate the minimum number of downpipes divide the roof catchment area by the allowable maximum catchment per downpipe.

Roof area per downpipe.

Downpipe fall fall fall fall fall roof pitch 45 figure 1 an example of a roof with a total plan area of 98 m. Size downspouts to fit the gutter. 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. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Sizing downpipes downpipes are sized for the areas that discharge into them. The 6 in 12 pitch factor 1 1 multiplied by 1 000 yields an effective area of 1 100 square feet. Doubling the number of downspouts halves the required capacity for each. This can be calculated using the following formula.

Using clause e1 table 5 see figure 2 at a roof pitch. Choosing the right style of guttering downpipes. Determine minimum number of downpipes. From figure 3 5 a in as nzs 3500 3 the maximum catchment per downpipe is 47m 2.

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. 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.

The answers for downpipe size are in mm. Working out the size of your roof. Select 100 x 50 rectangular downpipe. Multiplying that number by the local maximum rainfall intensity 6 8 inches per hour yields an adjusted square footage of 7 480 square feet.