Calculating Gutter And Downspout Needs

3 by 4 inches 1 200 square feet.

Calculating gutter and downspout needs. Ratio of depth to width of gutter calculate drainage reset. Rainfall intensity is measured in a 5 minute interval translated. Please lower the maximum spacing between downspouts to see this effect. This calculator uses the equations that are laid out in the smacna handbook.

Measure the roof to get the watershed area the area from which water will run off. To figure out what size gutters you need first you ll need to calculate the square footage of the gutter s drainage area. From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used. Metal era recommends that you verify all data obtained.

Now architects engineers designers and contractors can easily and accurately size downspouts and gutters according to the specifications in smacna s architectural sheet metal manual 7th edition 2012. Multiply length peak to. 15 m is a practical maximum gutter length to be served by a downspout. To limit the effects of thermal expansion in gutters 50 ft.

For a simple gable end roof you would only need to make two calculations one for each slope. This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end. As a general rule gutter slope is set at 1 4 inch per 10 feet of guttering. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. Divide 1600 sq ft 149 sq m by 160 sq ft sq in 2 3 sq m 100 sq mm to determine that each downspout should have a minimum area of 10 sq in 6470 sq mm. Downspout sizes must not exceed the bottom width of the gutter.

For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. 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. Minimum top opening width max length to.

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. Use the chart below to figure out how many extra downspouts you need. Max gutter per downspout ft storm requirement. Find the rainfall intensity for your locale.

The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. How to calculate gutter and downspout capacity step 1. From table 1 3 it is found that a4 in 102 mm downspout is required.