Calculating Gutter And Downspout Needs

I have seen several downspouts dented or bent due to mechanical damage.

Calculating gutter and downspout needs.

2 4 gutter and downspout sizing and location calculations. Doubling the number of downspouts halves the required capacity for each. The size of the downspout should be constant through out its length. 1 gutter channels that run horizontally along the roof edge to collect 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. The issue for downspouts isn t water capacity in a torrential rain it s debris that gets washed into the downspout. The larger the downspout the better debris will wash through.

Offset of more than 10 ft 3 0 m can affect drainage capacity. Gutters accessories. Size the gutters for the rainfall but go with the largest downspout that will fit your gutters. As you proceed keep in mind the different areas of your roof that you measured in section 2 2 calculating your roof area for rainwater harvesting.

Size downspouts to fit the gutter. Downspout sizes must not exceed the bottom width of the gutter. Downspouts should be constructed with conductor heads every 40 ft 12 2 m to admit air and prevent vacuum. 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 gutter outlet capacity should suit the downspout capacity. Quite often you will see downspouts that are short and discharge onto the roof which is. 3 by 4 inches 1 200 square. 2 by 3 inches 600 square feet.

Downspout empties onto the roof. Wood rot behind gutters. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Lots of times you will find that downspouts are missing from the gutter system.

This will dictate the amount of water that the gutter needs to be able to carry during the hardest rain storms. A damaged section of gutter. 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. Gutter systems consist of two parts.

1 24 of 395 results for tools home improvement. 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. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. 15 m is a practical maximum gutter length to be served by a downspout.

Roofing gutters should slope down toward the downspout at the rate of 1 16 inch per foot or 1 4 inch per 5 to 10 feet. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.