Calculate Rain Gutter Size

See photos below most residential gutters will measure approximately 5 inches across the top with the actual opening being approximately 4 5 inches.

Calculate rain gutter size.

Then use the chart below to see what size gutter you need. Find the width of the gutters. Run the tape measure from 1 corner of the gutter as far as you can go toward. Measure the roof to get the watershed area the area from which water will run off.

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. 15 m is a practical maximum gutter length to be served by a downspout. Find the rainfall intensity for your locale. To limit the effects of thermal expansion in gutters 50 ft.

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. How to calculate gutter and downspout capacity step 1. 5 inch standard k style gutter shop 5 gutterbrush.

Box gutter with rain water head at end of box gutter. Measure the length of each gutter run. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. The saf perimeter systems gutter downspout capacity table click to enlarge relates downspout size to gutter sizes.

In response smacna s technical resources department has created a free downspout and gutter sizing calculator. How do you calculate gutter size. Adjusting for pitch and rainfall. The steeper a roof s pitch the more windblown rain it can collect.

Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Downspout sizes must not exceed the bottom width of the gutter. Measuring existing gutters 1.

Rainfall intensity is measured in a 5 minute interval translated. Measure your gutter across the top from the back where the gutter meets the home to the outer edge. Measure the height of. 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.

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. 6 inch 7 960 square feet. Place a sturdy 20 ft 6 1 m ladder on 1 side of your house so that you can reach.