Calculate the total roof area by multiplying its length by width.
How many downspouts for roof.
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.
Use the chart below to figure out how many extra downspouts you need.
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.
First you must consider how many downspouts you will need.
Calculate total roof area.
Determine leader or pipe size.
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.
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.
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.
Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200.
Size downspouts to fit the gutter.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
Doubling the number of downspouts halves the required capacity for each.
Multiply the number of downspouts by square footage of each.
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.
A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate.
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.
2 by 3 inches 600 square feet.
As with gutters a downspout s capacity must match or exceed the expected runoff.
3 by 4 inches 1 200 square.
The typical recommendation is one downspout for every 20 to 30 feet of gutters.
Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area.
As with gutters a downspout s capacity must match or exceed the expected runoff.
A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour.
Buried or underground roof drainage downspout defects clogging overflowing holes corrosion leaks that cause wet basements or crawl areas proper installation of buried downspout extensions proper installation of french drains seepage pits at flat sites gutter downspout defects cause wet basements crawl areas questions answers about installing maintaining repairing buried roof.
