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.
Nrcs gutter and downspout sizing.
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.
Some trimming of the flange on the preformed outlet may be required.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
In sizing downspouts the following considerations apply.
A 6 inch top width k style gutter can receive a 3 x 4 downspout.
Use the chart below to figure out how many extra downspouts you need.
Please lower the maximum spacing between downspouts to see this effect.
15 m is a practical maximum gutter length to be served by a downspout.
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.
The size of the downspout should be constant through out its length.
A 3 x 4 downspout can also fit.
The sizes available in this style are 3 4 5 and 6.
To limit the effects of thermal expansion in gutters 50 ft.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter.
Round downspouts come in various sizes and colors and mostly used with half round gutters.
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.
Types of gutter downspouts.
Adding additional sections of gutter reduces the length of each section and will reduce the gutter size.
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.
Doubling the number of downspouts halves the required capacity for each.
There is a range of downspout styles which are available in the market as listed below.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
Typically a 5 inch top width k style gutter can receive a 2 x 3 downspout.
Size downspouts to fit the gutter.
