Calculate Rain Gutter Size

Match your downspouts to the gutter size you chose in step 7.

Calculate rain gutter size.

Downspout sizes must not exceed the bottom width of the gutter. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. The total rainfall and how rapidly it falls will affect the runoff from the roof. 5 inch 5 520 square feet.

If a roof s various drainage areas call for different size gutters go for the biggest one k style. Then use the chart below to see what size gutter you need. The code limit is 150mm for dp s and 26 800 sq mm for flat eaves gutters the program will calculate the size and number of downpipes downspouts leaders required and the eaves gutter sizes for any roof. Determine the size of your downspout.

Gutters typically come in 5 or 6 in 13 or 15 cm sizes and can be k style or half round place a sturdy 20 ft 6 1 m ladder on 1 side of your house so that you can reach the gutters. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. For example a 5 inch gutter system requires at least 2 x 3 downspouts and a 6 inch gutter system requires 3 x 4 downspouts. Gather some basic weather information to calculate the proper size for gutters and downspouts for a house.

Please lower the maximum spacing between downspouts to see this effect. Total roof area also affects runoff. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. 5 inch 5 520 square feet.

Simplified suitable for flattish roofs with little or no vertical faces or steep roofs draining to one side of box gutter only or any roof if you are in a hurry and make the necessary allowances for all catchments. Then use the information below to see what size gutter you need. Refer to the gutter packaging or specification for the recommended downspout size. Box gutter with rain water head at end of box gutter.

If a roof s various drainage areas call for different size gutters go for the biggest one k style. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. An inch of rain is not much but it if falls in half an hour it could flood a gutter.

6 inch 7 960 square feet. 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. There is no limit to downpipe size or eaves gutter size. 15 m is a practical maximum gutter length to be served by a downspout.