Gutter Downspout Requirements

Use the chart below to figure out how many extra downspouts you need.

Gutter downspout requirements. Come visit our selection of quality products. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. From table 1 3 it is found that a4 in 102 mm downspout is required. Welcome to gutter supply your online reference for gutters gutter machines gutter guards and accessories.

Size downspouts to fit the gutter. A general rule of thumb is one downspout per 20 feet of guttering but more may be necessary depending on the local weather the size of the drainage area and the design of the gutter system. The above recommendations assume that you have properly sized downspouts every 40 feet. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.

Poorly designed or installed gutters and downspouts can cause rainwater to pool around the base of the home or back up into the gutters. Allow 1 square inch of downspout cross section for every 100 square feet of roof area. As with gutters a downspout s capacity must match or exceed the expected runoff. Divide 1600 sq ft 149 sq m by 160 sq ft sq in 2 3 sq m 100 sq mm to determine that each downspout should have a minimum area of 10 sq in 6470 sq mm.

Doubling the number of downspouts halves the required capacity for each. From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used.