Sizing Residential Gutters

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.

Sizing residential gutters.

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. Residential sizing samples are available to check the optimal fit but in most cases the 5 half round gutter requires standard gutterbrush for 5 gutters 4 25 dia while the 6 half round gutter requires oversized gutterbrush for 6 gutters 5 25 dia. Roof area the locale s rainfall intensity and gutter capacity determine how many square inches of downspout are needed. However too large a gutter downspout can look unattractive.

Size downspouts to fit the gutter. The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. 6 inch 7 960 square feet. 5 inch 5 520 square feet.

Then use the information below to see what size gutter you need. 5 inch 5 520 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. If a roof s various drainage areas call for different size gutters go for the biggest one k style.

Once you are done deciding the correct size for your downspout depending upon the size of your gutter and the amount of rainfall in your area the next step shall be figuring out the kind of downspouts you want installed gpm stands for gallons per minute. Then use the chart below to see what size gutter you need. The larger a gutter downspout the more water it can drain quickly. Half round and k style gutters are the two most common gutter types found on residential homes.

Doubling the number of downspouts halves the required capacity for each. If frequent heavy showers occur where you live then a down spout with a bigger size would prove more suitable. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.

Most downspouts are rectangular but they can also be round or square. You should have enough gutter downspouts to effectively handle the size of your entire gutter system. Gutter downspout sizes are 3 to 6 inches. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.

If a roof s various drainage areas call for different size gutters go for the biggest one k style. How to size gutters downspouts.