Gutter And Downspout Design Calculations

Roof in the calculation of a drainage system.

Gutter and downspout design calculations.

The first is to make it wide and deep enough to collect all of the rainwater during the hardest rainfall. To determine the design area for a pitched roof table 1 1 is used. 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. 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. 15 m is a practical maximum gutter length to be served by a downspout. There are two major factors to consider when deciding a gutter design. 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.

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. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. To limit the effects of thermal expansion in gutters 50 ft. Table 1 1 design areas for pitched roofs pitch in ft.

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. Experience has taught that use of the true area of a pitched roof often leads to oversizing of gutters downspouts and drains. Doubling the number of downspouts halves the required capacity for each. Downspout sizes must not exceed the bottom width of the gutter.

Adding additional sections of gutter reduces the length of each section and will reduce the gutter size.