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 square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Use the chart below to figure out how many extra downspouts you need.
A 6 inch top width k style gutter can receive a 3 x 4 downspout.
As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter.
Please lower the maximum spacing between downspouts to see this effect.
Adding additional sections of gutter reduces the length of each section and will reduce the gutter size.
15 m is a practical maximum gutter length to be served by a downspout.
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.
There is a range of downspout styles which are available in the market as listed below.
Round downspouts come in various sizes and colors and mostly used with half round gutters.
Size downspouts to fit the gutter.
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.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters 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.
Gutter professionals have experience matching the gutters and the downspouts.
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.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
However 7 and 8 inches are available although the larger sizes are more suitable for larger buildings or business properties.
Downspout sizes must not exceed the bottom width of the gutter.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
A 3 x 4 downspout can also fit.
The size of the downspout should be constant through out its length.
Types of gutter downspouts.
To limit the effects of thermal expansion in gutters 50 ft.
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.
Also the gutter width in relation to height may also be adjusted.
In sizing downspouts the following considerations apply.
