Gutter And Downspout Design Calculations

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.

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. With 1 gpm 0 063 l s flow rate. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. 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.

Adding additional sections of gutter reduces the length of each section and will reduce the gutter size. Roof in the calculation of a drainage system. Downspout sizes must not exceed the bottom width of the gutter. Table 1 1 design areas for pitched roofs pitch in ft.

Downspouts and gutters are sized in relation to rainfall on this basis. Size downspouts to fit the gutter. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. The first is to make it wide and deep enough to collect all of the rainwater during the hardest rainfall.

To limit the effects of thermal expansion in gutters 50 ft. Doubling the number of downspouts halves the required capacity for each. To determine the design area for a pitched roof table 1 1 is used. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.

Experience has taught that use of the true area of a pitched roof often leads to oversizing of gutters downspouts and drains.