Sizing Of Roof Downspouts

Downspouts of less than 7 00 sq in 4515 sq mm cross section should not be used except for small areas such as porches and canopies.

Sizing of roof downspouts.

Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Please lower the maximum spacing between downspouts to see this effect. Doubling the number of downspouts halves the required capacity for each.

Size downspouts to fit the gutter. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Downspouts should be constructed with conductor. Then use the information below to see what size gutter you need.

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. 5 inch 5 520 square feet. Now architects engineers designers and contractors can easily and accurately size downspouts and gutters according to the specifications in smacna s architectural sheet metal manual 7th edition 2012.

If a roof s various drainage areas call for different size gutters go for the biggest one k style.