Calculate Rain Gutter Size

Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.

Calculate rain gutter size.

Measure the roof to get the watershed area the area from which water will run off. Water capacity values of a gutter downspout system is calculated using the height head of water a gutter can hold the outlet orifice size of the downspout and the quantity of downspouts used. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted. Find the width of the gutters.

The steeper a roof s pitch the more windblown rain it can collect. Measuring existing gutters 1. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. How do you calculate gutter size.

The saf perimeter systems gutter downspout capacity table click to enlarge relates downspout size to gutter sizes. Adjusting for pitch and rainfall. Multiply length peak to. 5m x 4m x 4 2 40 square metres.

The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. If a roof s various drainage areas call for different size gutters go for the biggest one k style. 15 m is a practical maximum gutter length to be served by a downspout. Calculate the area of a roof to work out how much guttering is required so for a roof that is 5 m long with a height of 4 m and the roof width is 8 m which makes the half roof width 4m we can calculate the effective roof area like this.

Measure the height of. 6 inch 7 960 square feet. Rainfall intensity is measured in a 5 minute interval translated. Downspout sizes must not exceed the bottom width of the gutter.

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. See photos below most residential gutters will measure approximately 5 inches across the top with the actual opening being approximately 4 5 inches. 5 inch 5 520 square feet. In response smacna s technical resources department has created a free downspout and gutter sizing calculator.

Place a sturdy 20 ft 6 1 m ladder on 1 side of your house so that you can reach. Find the rainfall intensity for your locale. How to calculate gutter and downspout capacity step 1. Measure the length of each gutter run.

Run the tape measure from 1 corner of the gutter as far as you can go toward. Simplified suitable for flattish roofs with little or no vertical faces or steep roofs draining to one side of box gutter only or any roof if you are in a hurry and make the necessary allowances for all catchments. Then use the chart below to see what size gutter you need. 5 inch standard k style gutter shop 5 gutterbrush.