Nrcs Gutter And Downspout Sizing

Please lower the maximum spacing between downspouts to see this effect.

Nrcs gutter and downspout sizing.

The sizes available in this style are 3 4 5 and 6. 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. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Use the chart below to figure out how many extra downspouts you need.

To limit the effects of thermal expansion in gutters 50 ft. Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. The size of the downspout should be constant through out its length. As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter.

A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. Some trimming of the flange on the preformed outlet may be required. Types of gutter downspouts. There is a range of downspout styles which are available in the market as listed below.

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. Round downspouts come in various sizes and colors and mostly used with half round gutters. Downspout sizes must not exceed the bottom width of the gutter. A 6 inch top width k style gutter can receive a 3 x 4 downspout.

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Size downspouts to fit the gutter. A 3 x 4 downspout can also fit. 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.

However 7 and 8 inches are available although the larger sizes are more suitable for larger buildings or business properties. 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. Doubling the number of downspouts halves the required capacity for each. Typically a 5 inch top width k style gutter can receive a 2 x 3 downspout.

As with gutters a downspout s capacity must match or exceed the expected runoff. 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. 15 m is a practical maximum gutter length to be served by a downspout. Gutter professionals have experience matching the gutters and the downspouts.

In sizing downspouts the following considerations apply.