Multiply the number of downspouts by square footage of each.
How many downspouts for roof.
Rectangular downspouts move slightly less water at 600 square feet for 2 by 3 inch or 1 200 square feet for a 3 by 4 inch downspout.
Smacna s new downspout and gutter sizing calculator enables the user to manually enter the design area of the roof or use the design area wizard for the calculation.
The next factor to take into account is the pitch of your roof because the pitch will cause water to flow in a certain direction.
There are 5 easy steps to figure out how many drains your commercial roofing project will need.
Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.
Rain gutters and downspouts provide an efficient first step in controlling roof runoff.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Use the chart below to figure out how many extra downspouts you need.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Calculate the total roof area by multiplying its length by width.
2 by 3 inches 600 square feet.
This wizard makes it easy to calculate the roof design area by providing various shape calculations and the calculation for vertical walls area per international plumbing code ipc.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
Calculate total roof area.
Use the chart below to figure out how many extra downspouts you need.
A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate.
Determine leader or pipe size.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
A high slope moves water more quickly and if gutters have trouble dealing with a lot of water in a short period of time an extra downspout can alleviate that issue.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200.
3 by 4 inches 1 200 square.
Gutters come in many sizes.
The typical recommendation is one downspout for every 20 to 30 feet of gutters.
Size downspouts to fit the gutter.
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