To limit the effects of thermal expansion in gutters 50 ft.
Nrcs gutter and downspout sizing.
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 3 x 4 downspout can also fit.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Gutter professionals have experience matching the gutters and the downspouts.
Downspout sizes must not exceed the bottom width of the gutter.
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.
Use the chart below to figure out how many extra downspouts you need.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
Typically a 5 inch top width k style gutter can receive a 2 x 3 downspout.
Some trimming of the flange on the preformed outlet may be required.
Round downspouts come in various sizes and colors and mostly used with half round gutters.
Size downspouts to fit the gutter.
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.
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.
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.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
In sizing downspouts the following considerations apply.
Types of gutter downspouts.
A 6 inch top width k style gutter can receive a 3 x 4 downspout.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
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.
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.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
As with gutters a downspout s capacity must match or exceed the expected runoff.
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 additional sections of gutter reduces the length of each section and will reduce the gutter size.
