Sizing Of Roof Downspouts

Please lower the maximum spacing between downspouts to see this effect.

Sizing of roof downspouts.

The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. The size of the downspout should be constant through out its length. 5 inch 5 520 square feet. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.

If a roof s various drainage areas call for different size gutters go for the biggest one k style. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Doubling the number of downspouts halves the required capacity for each. Downspout sizing in sizing downspouts the following considerations apply.

Then use the information below to see what size gutter you need. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. 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.

Size downspouts to fit the gutter.