How To Size Number Of Downspouts Needed For Roof

Downspout sizing in sizing downspouts the following considerations apply.

How to size number of downspouts needed for roof.

The capacity of a sloped rectangular gutter may be approximated by using a gutter cross section area not less than that of a semicircular gutter and a depth to width ratio of at least 0 75. Downspouts should be constructed with conductor. Also the gutter width in relation to height may also be adjusted. If a roof s various drainage areas call for different size gutters go for the biggest one k style.

The gutter and downspout size requirement depends upon the number of sections and length of the gutter sections as well as the number of downspouts. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Multiply the number of downspouts by square footage of each. Size downspouts to fit the gutter.

Rectangular downspouts move slightly less water at 600 square feet for 2 by 3 inch or 1 200 square feet for a 3 by 4 inch downspout. Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. Downspout sizes must not exceed the bottom width of the gutter. 6 inch 7 960 square feet.

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. To limit the effects of thermal expansion in gutters 50 ft. 15 m is a practical maximum gutter length to be served by a downspout. 5 inch 5 520 square feet.

Doubling the number of downspouts halves the required capacity for each. Then use the information below to see what size gutter you need.