Calculating Gutter And Downspout Needs

Gutter systems consist of two parts.

Calculating gutter and downspout needs.

Downspout empties onto the roof. Wood rot behind gutters. As with gutters a downspout s capacity must match or exceed the expected runoff. Gutters accessories.

The gutter outlet capacity should suit the downspout capacity. Downspouts should be constructed with conductor heads every 40 ft 12 2 m to admit air and prevent vacuum. 1 gutter channels that run horizontally along the roof edge to collect runoff. The size of the downspout should be constant through out its length.

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. A damaged section of gutter. And 2 the downspouts that carry the collected water to grade level. I have seen several downspouts dented or bent due to mechanical damage.

The issue for downspouts isn t water capacity in a torrential rain it s debris that gets washed into the downspout. Use the chart below to figure out how many extra downspouts you need. Lots of times you will find that downspouts are missing from the gutter system. The larger the downspout the better debris will wash through.

Size downspouts to fit the gutter. 2 by 3 inches 600 square feet. 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 downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.

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. Offset of more than 10 ft 3 0 m can affect drainage capacity. Size the gutters for the rainfall but go with the largest downspout that will fit your gutters. This will dictate the amount of water that the gutter needs to be able to carry during the hardest rain storms.

3 by 4 inches 1 200 square. 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. 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. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed.

Gutter downspouts welcome to the gutter downspouts store where you ll find great prices on a wide range of different gutter downspouts for your home. 1 24 of 395 results for tools home improvement. Quite often you will see downspouts that are short and discharge onto the roof which is. 15 m is a practical maximum gutter length to be served by a downspout.

Doubling the number of downspouts halves the required capacity for each. To limit the effects of thermal expansion in gutters 50 ft.