Calculate How Many Downspouts Gutters Need

If we have to sum it up in a single rule gutters need a downspout around every 30 to 40 feet.

Calculate how many downspouts gutters need.

Remember two gutter lengths can share the same downspout so if you calculate the max gutter to be 40 feet you could put a downspout halfway in an 80 foot length. Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. 5 gutters typically use 2 3 downspouts. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.

For most homes this means installing spouts at either end of a gutter section. For hipped roofs with eaves gutters a simplified formula can be used to calculate catchment area but the slope of the roof must be known. Refer to as nzs 3500 3. 6 k gutter is used for higher volume of water runoff to a single point typically on flat roofs or larger commercial buildings.

The catchment area of a roof and any vertical walls is greatly influenced by the direction of wind driven rain therefore the combined catchment area must be used for sizing purposes. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. As with gutters a downspout s capacity must match or exceed the expected runoff. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.

How to calculate gutter and downspout capacity step 1. Once you add up the square footage of your roof you can then determine the number of downspouts. 6 gutters typically use 3 4 downspouts to accommodate higher volume of water. It is used in 95 of all installations and works for all sloped roofing materials shingles metal slate wood etc.

Use the chart below to figure out how many extra downspouts you need. 2 by 3 inches 600 square feet. Use the chart below to figure out how many extra downspouts you need. How many downspout installations should your gutters have.

Hello bb10 and welcome to the community. Enter larger gutter widths in the yellow boxes to find out how wide your gutters need to be given the length that you want to go between downspouts. 15 m is a practical maximum gutter length to be served by a downspout. To limit the effects of thermal expansion in gutters 50 ft.

Find the rainfall intensity for your locale. 3 by 4 inches 1 200 square feet. Multiply length peak to. Measure the roof to get the watershed area the area from which water will run off.

Rainfall intensity is measured in a 5 minute interval translated. As with gutters a downspout s capacity must match or exceed the expected runoff. Minimum top opening width max. The number of downspouts can be determined by the surface square feet of your roof.

3200 square feet of roof is calculated as 3200 600 5 33 rounding up you would need 6 2x3 downspouts. There is no limit to downpipe size or eaves gutter size.