Nrcs Gutter And Downspout Sizing

Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.

Nrcs gutter and downspout sizing.

A 3 x 4 downspout can also fit. Downspout sizes must not exceed the bottom width of the gutter. Types of gutter downspouts. Doubling the number of downspouts halves the required capacity for each.

Some trimming of the flange on the preformed outlet may be required. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. A 6 inch top width k style gutter can receive a 3 x 4 downspout. 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. As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. 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.

15 m is a practical maximum gutter length to be served by a downspout. The size of the downspout should be constant through out its length. The sizes available in this style are 3 4 5 and 6. In sizing downspouts the following considerations apply.

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. To limit the effects of thermal expansion in gutters 50 ft. 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. There is a range of downspout styles which are available in the market as listed below.

Size downspouts to fit the gutter. Round downspouts come in various sizes and colors and mostly used with half round gutters. 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 additional sections of gutter reduces the length of each section and will reduce the gutter size.

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. 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. Please lower the maximum spacing between downspouts to see this effect. However 7 and 8 inches are available although the larger sizes are more suitable for larger buildings or business properties.

Gutter professionals have experience matching the gutters and the downspouts.