How To Size Number Of Downspouts Needed For Roof

Also the gutter width in relation to height may also be adjusted.

How to size number of downspouts needed for roof.

If a roof s various drainage areas call for different size gutters go for the biggest one k style. 5 inch 5 520 square feet. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Then use the information below to see what size gutter you need.

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. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. 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. Size downspouts to fit the gutter.

The size of the downspout should be constant through out its length. 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. 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. Downspout sizing in sizing downspouts the following considerations apply.

Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. 15 m is a practical maximum gutter length to be served by a downspout. Doubling the number of downspouts halves the required capacity for each. Multiply the number of downspouts by square footage of each.

To limit the effects of thermal expansion in gutters 50 ft. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.