In response smacna s technical resources department has created a free downspout and gutter sizing calculator.
Calculate rain gutter size.
15 m is a practical maximum gutter length to be served by a downspout.
Measure the roof to get the watershed area the area from which water will run off.
Adjusting for pitch and rainfall.
5 inch 5 520 square feet.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
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.
Box gutter with rain water head at end of box gutter.
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.
How to calculate gutter and downspout capacity step 1.
How do you calculate gutter size.
Run the tape measure from 1 corner of the gutter as far as you can go toward.
The steeper a roof s pitch the more windblown rain it can collect.
Measure your gutter across the top from the back where the gutter meets the home to the outer edge.
5 inch standard k style gutter shop 5 gutterbrush.
Measure the height of.
Multiply length peak to.
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.
Rainfall intensity is measured in a 5 minute interval translated.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
6 inch 7 960 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.
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.
Measuring existing gutters 1.
If a roof s various drainage areas call for different size gutters go for the biggest one k style.
Place a sturdy 20 ft 6 1 m ladder on 1 side of your house so that you can reach.
To limit the effects of thermal expansion in gutters 50 ft.
The saf perimeter systems gutter downspout capacity table click to enlarge relates downspout size to gutter sizes.
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.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted.
5m x 4m x 4 2 40 square metres.
Then use the chart below to see what size gutter you need.
