Calculate How Many Downspouts Gutters Need

There are many more important factors that can change this broad rule.

Calculate how many downspouts gutters need.

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. The number of downspouts can be determined by the surface square feet of your roof. 6 gutters typically use 3 4 downspouts to accommodate higher volume of water. The code limit is 150mm for dp s and 26 800 sq mm for flat eaves gutters the program will calculate the size and number of downpipes downspouts leaders required and the eaves gutter sizes for any roof.

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. Use the chart below to figure out how many extra downspouts you need. 2 by 3 inches 600 square feet.

Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. 3 by 4 inches 1 200 square feet. If we have to sum it up in a single rule gutters need a downspout around every 30 to 40 feet. 5 gutters typically use 2 3 downspouts.

For most homes this means installing spouts at either end of a gutter section. 6 k gutter is used for higher volume of water runoff to a single point typically on flat roofs or larger commercial buildings. To limit the effects of thermal expansion in gutters 50 ft. 15 m is a practical maximum gutter length to be served by a downspout.

Once you add up the square footage of your roof you can then determine the number of downspouts. Hello bb10 and welcome to the community. 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. There is no limit to downpipe size or eaves gutter size.

3200 square feet of roof is calculated as 3200 600 5 33 rounding up you would need 6 2x3 downspouts. As with gutters a downspout s capacity must match or exceed the expected runoff. Refer to as nzs 3500 3. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.

Downspout sizes must not exceed the bottom width of the gutter. Multiply length peak to. 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. As with gutters a downspout s capacity must match or exceed the expected runoff.

Minimum top opening width max. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. 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. Use the chart below to figure out how many extra downspouts you need.

Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. It is used in 95 of all installations and works for all sloped roofing materials shingles metal slate wood etc.