Use the chart below to figure out how many extra downspouts you need.
Gutter downspout capacity.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Use the helpful charts below and you ll be a near expert in no time.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
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Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200.
The downspout size must suit the bottom width of the gutter.
So what s the trick to designing the perfect gutter system.
The risk of rain gutter overflow from insufficient drainage capacity.
It is possible to use a mix of gutter sizes a mix of downspout sizes and quantities to accommodate the theoretical gallons per minute draining.
A scupper serving a designated roof area ï after the number and location of downspouts have been determined the areas to be drained by each downspout should be figured.
Gutter and downspout water capacity.
Use the chart below to figure out how many extra downspouts you need.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Design of roof drainage systems roof drainage the roof is one of the most essential parts of a building as it protects occupants contents and interior of the structure from the elements.
The capacity of a sloped rectangular gutter may be approximated by using a gutter cross section area not less than that of a semicircular gutter and.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
Size downspouts to fit the gutter.
These are safe numbers meaning designed to work under the strongest rainfall not the average for.
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.
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.
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.
Downspout sizes must not exceed the bottom width of the gutter.
3 by 4 inches 1 200 square.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Doubling the number of downspouts halves the required capacity for each.
How to make sure your gutter is large enough and you have enough downspouts.
