How To Size Number Of Downspouts Needed For Roof

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.

How to size number of downspouts needed for roof.

15 m is a practical maximum gutter length to be served by a downspout. Downspout sizes must not exceed the bottom width of the gutter. Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. If a roof s various drainage areas call for different size gutters go for the biggest one k style.

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. Multiply the number of downspouts by square footage of each. Then use the information below to see what size gutter you need. 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.

Downspout sizing in sizing downspouts the following considerations apply. Downspouts should be constructed with conductor. The size of the downspout should be constant through out its length. 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. 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. Also the gutter width in relation to height may also be adjusted.

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. Size downspouts to fit the gutter.