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.
Calculating gutter and downspout needs.
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.
Ratio of depth to width of gutter calculate drainage reset.
Please lower the maximum spacing between downspouts to see this effect.
As a general rule gutter slope is set at 1 4 inch per 10 feet of guttering.
2 by 3 inches 600 square feet.
To limit the effects of thermal expansion in gutters 50 ft.
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.
How to calculate gutter and downspout capacity step 1.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
To figure out what size gutters you need first you ll need to calculate the square footage of the gutter s drainage area.
Minimum top opening width max length to.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used.
Measure the roof to get the watershed area the area from which water will run off.
Max gutter per downspout ft storm requirement.
15 m is a practical maximum gutter length to be served by a downspout.
3 by 4 inches 1 200 square feet.
Find the rainfall intensity for your locale.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
Metal era recommends that you verify all data obtained.
From table 1 3 it is found that a4 in 102 mm downspout is required.
The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts.
For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e.
This calculator serves as an information source only.
For a simple gable end roof you would only need to make two calculations one for each slope.
As with gutters a downspout s capacity must match or exceed the expected runoff.
This calculator uses the equations that are laid out in the smacna handbook.
Use the chart below to figure out how many extra downspouts you need.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
Rainfall intensity is measured in a 5 minute interval translated.
This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end.
