Gutter And Downspout Design Calculations

Size downspouts to fit the gutter.

Gutter and downspout design calculations. This spread sheet will help you calculate the gutter width and maximum distance between downspouts based on your maximum rainfall roof area and style of gutter. 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. Roof in the calculation of a drainage system. This wizard makes it easy to calculate the roof design area by providing various shape calculations and the calculation for vertical walls area per international plumbing code ipc.

Table 1 1 design areas for pitched roofs pitch in ft. Experience has taught that use of the true area of a pitched roof often leads to oversizing of gutters downspouts and drains. 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.

Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. Downspout sizes must not exceed the bottom width of the gutter. Plumbing codes typically use the vertically projected roof area for drainage design and they often use a square foot allowance per square inch of downspout for 1 in hr 25 mm hr rainfall that varies with diameter for example 3. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.

Downspouts and gutters are sized in relation to rainfall on this basis. To determine the design area for a pitched roof table 1 1 is used. To limit the effects of thermal expansion in gutters 50 ft. There are two major factors to consider when deciding a gutter design.

The first is to make it wide and deep enough to collect all of the rainwater during the hardest rainfall.