Gutter Downspout Capacity

However too large a gutter downspout can look unattractive.

Gutter downspout capacity.

Most of all is location and your average rainfall during a large downpour. As with gutters a downspout s capacity must match or exceed the expected runoff. Downspout sizing in sizing downspouts the following considerations apply. Increasing the pitch increases a gutter s handling capacity but the gutter may look askew over a long run.

You should have enough gutter downspouts to effectively handle the size of your entire gutter system. As with gutters a downspout s capacity must match or exceed the expected runoff. Adding a 2 by 3 rectangular downspout for instance boosts your gutter s capacity by 600 square feet of drainage area. Many factors can effect the proper size of gutter.

Rectangular 2 by 3 inches 600 square feet 3 by 4 inches 1 200. Problems with gutter sizing. Capacity from using table 1 1 and 1 2 should be com pared with local code requirements. The above recommendations assume that you have properly sized downspouts every 40 feet.

Now that we are well aware of the various gutter downspout sizes and styles let us dig deeper into the materials used for effective downspouts and how much they shall cost. Downspout sizes must not exceed the bottom width of the gutter. Gutter professionals have experience matching the gutters and the downspouts. The standard is about inch per 10 feet.

Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Size downspouts to fit the gutter. Most downspouts are rectangular but they can also be round or square. The larger a gutter downspout the more water it can drain quickly.

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. 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. Use the chart below to figure out how many extra downspouts you need.

As far as downspouts go they run at 2 x3 and 3 x4 in size or 3 or 4 inches in diameter. Downspout sizes are based on table 1 3 dimensions of standard downspouts page 1 4 of the architectural sheet metal manual 7th edition. Doubling the number of downspouts halves the required capacity for each. Gutter downspout sizes are 3 to 6 inches.

The second most common style of downspouts in urban homes is the rectangular downspout coming under a range of sizes such as 2 3 3 4 and 4 5. Primary cause for water spillage is debri in the gutter. For the vast majority of rains gutter and downspouts sizes considerably less than recommended will do the job. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.