Nrcs Gutter And Downspout Sizing

Also the gutter width in relation to height may also be adjusted.

Nrcs gutter and downspout sizing.

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. As with gutters a downspout s capacity must match or exceed the expected runoff. To limit the effects of thermal expansion in gutters 50 ft. Types of gutter downspouts.

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. A 6 inch top width k style gutter can receive a 3 x 4 downspout. Size downspouts to fit the gutter. 15 m is a practical maximum gutter length to be served by a downspout.

Typically a 5 inch top width k style gutter can receive a 2 x 3 downspout. Please lower the maximum spacing between downspouts to see this effect. Gutter professionals have experience matching the gutters and the downspouts. 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.

Use the chart below to figure out how many extra downspouts you need. However 7 and 8 inches are available although the larger sizes are more suitable for larger buildings or business properties. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. The size of the downspout should be constant through out its length.

The sizes available in this style are 3 4 5 and 6. 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. 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. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. Downspout sizes must not exceed the bottom width of the gutter. Round downspouts come in various sizes and colors and mostly used with half round gutters.

As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter. Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. A 3 x 4 downspout can also fit.

Doubling the number of downspouts halves the required capacity for each.