There are 5 easy steps to figure out how many drains your commercial roofing project will need.
How many downspouts for roof.
But if the rain or melted snow channeled off the roof isn t carried far enough away from the house it will collect against the foundation wall or footing and seep into your basement or crawl space.
Use the chart below to figure out how many extra downspouts you need.
2 by 3 inches 600 square feet.
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.
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Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
The typical recommendation is one downspout for every 20 to 30 feet of gutters.
A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate.
Calculate total roof area.
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.
Gutters come in many sizes.
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.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Size downspouts to fit the gutter.
As with gutters a downspout s capacity must match or exceed the expected runoff.
Rain gutters and downspouts provide an efficient first step in controlling roof runoff.
Multiply the number of downspouts by square footage of each.
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.
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.
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.
Calculate the total roof area by multiplying its length by width.
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.
As with gutters a downspout s capacity must match or exceed the expected runoff.
3 by 4 inches 1 200 square.
