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.
Calculate rain gutter size.
Measure the height of.
Find the width of the gutters.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.
How to calculate gutter and downspout capacity step 1.
Run the tape measure from 1 corner of the gutter as far as you can go toward.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
Find the rainfall intensity for your locale.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
Box gutter with rain water head at end of box gutter.
Measure the roof to get the watershed area the area from which water will run off.
Measuring existing gutters 1.
How do you calculate gutter size.
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.
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.
Measure the length of each gutter run.
Rainfall intensity is measured in a 5 minute interval translated.
5 inch standard k style gutter shop 5 gutterbrush.
Downspout sizes must not exceed the bottom width of the gutter.
6 inch 7 960 square feet.
To limit the effects of thermal expansion in gutters 50 ft.
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.
15 m is a practical maximum gutter length to be served by a downspout.
Adjusting for pitch and rainfall.
Multiply length peak to.
The steeper a roof s pitch the more windblown rain it can collect.
5m x 4m x 4 2 40 square metres.
If a roof s various drainage areas call for different size gutters go for the biggest one k style.
Then use the chart below to see what size gutter you need.
5 inch 5 520 square feet.
See photos below most residential gutters will measure approximately 5 inches across the top with the actual opening being approximately 4 5 inches.
In response smacna s technical resources department has created a free downspout and gutter sizing calculator.
