Calculate How Many Downspouts Gutters Need

Refer to as nzs 3500 3.

Calculate how many downspouts gutters need.

It is used in 95 of all installations and works for all sloped roofing materials shingles metal slate wood etc. As with gutters a downspout s capacity must match or exceed the expected runoff. The number of downspouts can be determined by the surface square feet of your roof. 5 gutters typically use 2 3 downspouts.

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. There is no limit to downpipe size or eaves gutter size. Find the rainfall intensity for your locale. To limit the effects of thermal expansion in gutters 50 ft.

Once you add up the square footage of your roof you can then determine the number of downspouts. 3 by 4 inches 1 200 square feet. 15 m is a practical maximum gutter length to be served by a downspout. 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. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. Rainfall intensity is measured in a 5 minute interval translated. 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.

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. 2 by 3 inches 600 square feet. Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200 square feet. Hello bb10 and welcome to the community.

Use the chart below to figure out how many extra downspouts you need. 3200 square feet of roof is calculated as 3200 600 5 33 rounding up you would need 6 2x3 downspouts. How to calculate gutter and downspout capacity step 1. Measure the roof to get the watershed area the area from which water will run off.

Multiply length peak to. Use the chart below to figure out how many extra downspouts you need. If we have to sum it up in a single rule gutters need a downspout around every 30 to 40 feet. 6 k gutter is used for higher volume of water runoff to a single point typically on flat roofs or larger commercial buildings.

Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Minimum top opening width max. 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. As with gutters a downspout s capacity must match or exceed the expected runoff.

6 gutters typically use 3 4 downspouts to accommodate higher volume of water. There are many more important factors that can change this broad rule.