How To Size Number Of Downspouts Needed For Roof

The size of the downspout should be constant through out its length.

How to size number of downspouts needed for roof.

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Downspout sizes must not exceed the bottom width of the gutter. 5 inch 5 520 square feet. Multiply the number of downspouts by square footage of each.

Also the gutter width in relation to height may also be adjusted. 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. 6 inch 7 960 square feet.

Size downspouts to fit the gutter. Downspouts should be constructed with conductor. Doubling the number of downspouts halves the required capacity for each. 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.

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. Then use the information below to see what size gutter you need. 15 m is a practical maximum gutter length to be served by a downspout. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.

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