Nrcs Gutter And Downspout Sizing

Gutter professionals have experience matching the gutters and the downspouts.

Nrcs gutter and downspout sizing. The size of the downspout should be constant through out its length. However 7 and 8 inches are available although the larger sizes are more suitable for larger buildings or business properties. A 6 inch top width k style gutter can receive a 3 x 4 downspout. The sizes available in this style are 3 4 5 and 6.

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. Some trimming of the flange on the preformed outlet may be required. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. 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.

Also the gutter width in relation to height may also be adjusted. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. Five inch k style gutters or 6 inch half rounds the most common residential sizes are able to handle the rainfall on most houses in most parts of the country. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.

15 m is a practical maximum gutter length to be served by a downspout. Please lower the maximum spacing between downspouts to see this effect. As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter. But houses with big steep roofs or those located in climates prone to heavy downpours may need wider gutters and extra downspouts to keep rainwater from overflowing.

Size downspouts to fit the gutter. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Doubling the number of downspouts halves the required capacity for each.

A 3 x 4 downspout can also fit. Also please adjust the gutter width relation to height as some width height ratios will not be compatible with standard gutter sizes and the calculator will recommend a custom gutter. Typically a 5 inch top width k style gutter can receive a 2 x 3 downspout. To limit the effects of thermal expansion in gutters 50 ft.

Downspout sizes must not exceed the bottom width of the gutter. As with gutters a downspout s capacity must match or exceed the expected runoff. Use the chart below to figure out how many extra downspouts you need. Types of gutter downspouts.

There is a range of downspout styles which are available in the market as listed below.