This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end.
Calculating gutter and downspout needs.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
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.
15 m is a practical maximum gutter length to be served by a downspout.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e.
Find the rainfall intensity for your locale.
Rainfall intensity is measured in a 5 minute interval translated.
Measure the roof to get the watershed area the area from which water will run off.
As a general rule gutter slope is set at 1 4 inch per 10 feet of guttering.
Downspout sizes must not exceed the bottom width of the gutter.
This calculator uses the equations that are laid out in the smacna handbook.
As with gutters a downspout s capacity must match or exceed the expected runoff.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
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.
Divide 1600 sq ft 149 sq m by 160 sq ft sq in 2 3 sq m 100 sq mm to determine that each downspout should have a minimum area of 10 sq in 6470 sq mm.
Minimum top opening width max length to.
For a simple gable end roof you would only need to make two calculations one for each slope.
2 by 3 inches 600 square feet.
To limit the effects of thermal expansion in gutters 50 ft.
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.
3 by 4 inches 1 200 square feet.
Ratio of depth to width of gutter calculate drainage reset.
From chart 1 2 it is determined that a 9 5 in 241 mm half round gutter should be used.
Use the chart below to figure out how many extra downspouts you need.
Max gutter per downspout ft storm requirement.
To figure out what size gutters you need first you ll need to calculate the square footage of the gutter s drainage area.
How to calculate gutter and downspout capacity step 1.
The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts.
Please lower the maximum spacing between downspouts to see this effect.
This calculator serves as an information source only.
