Roof Square Footage Per Downspout

2 3 4 5 6 and 8 in.

Roof square footage per downspout.

Measure your house at ground level then add in the roof s overhang for greater accuracy. You would divide 35 4 by 129 to get the average of 274 inches per event. As with gutters a downspout s capacity must match or exceed the expected runoff. 2 3 4 5 6 and 8 in.

Max area of roof draining to one down. Gutters come in many sizes. Multiply the two figures together to obtain the square footage of your roof. 3 inches 706 square feet.

Size downspouts to fit the gutter. In cases where a roof has a complex shape such as in the image to the right measuring the dimensions and areas of each part of the roof to calculate total area will result in a more accurate measurement of area. The calculator cannot account for complex shapes based on a measurement of square footage alone. Calculate the total roof area by multiplying its length by width.

4 inches 1 255. 2 by 3 inches 600 square feet. 3 by 4 inches 1 200 square feet. So continuing our example if you ve got a two story house with a total square footage of 2 700 square feet with each floor having 1 350 square feet multiply 1 350 by 1 0541 to get 1 423 square.

A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate. Use the chart below to figure out how many extra downspouts you need. Determine leader or pipe size. If i see a gutter that is over 30 or 40 feet long with only one downspout i always want to see the bigger 4 or 5 inch gutters installed with the 3 x 4 downspout in order for it to handle the amount of water it will be discharging.

As an example if your overhang is 12 inches you ll add 2 feet to the overall length and 2 feet to the overall width of the house. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Calculate total roof area. A round downspout is slightly more efficient in draining water than square or rectangular ones.

Roof pitches in degrees. Following are the standard sizes for some of the top manufacturers. Doubling the number of downspouts halves the required capacity for each. This nominal square footage amount is then multiplied by a factor associated with the roof s pitch.

Calculate the area of square footage that each downspout will be collecting from in a rainfall a. A square inch of downspout can drain 1 200 square feet of roof during a rain with an intensity of one inch per hour. The above recommendations assume that you have properly sized downspouts every 40 feet.