Gutter Downspout Requirements

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.

Gutter downspout requirements.

Size downspouts to fit the gutter. Use the chart below to figure out how many extra downspouts you need. Gutters and downspouts need to be sized to accommodate anticipated water loads. Welcome to gutter supply your online reference for gutters gutter machines gutter guards and accessories.

Come visit our selection of quality products. From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used. From table 1 3 it is found that a4 in 102 mm downspout is required. Place downspouts at least 20 feet apart but no more than 50 feet apart.

Doubling the number of downspouts halves the required capacity for each. 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. Allow 1 square inch of downspout cross section for every 100 square feet of roof area. The above recommendations assume that you have properly sized downspouts every 40 feet.

Poorly designed or installed gutters and downspouts can cause rainwater to pool around the base of the home or back up into the gutters. As with gutters a downspout s capacity must match or exceed the expected runoff.