Calculate Rain Gutter Size

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.

Calculate rain gutter size.

The total rainfall and how rapidly it falls will affect the runoff from the roof. Find the width of the gutters. Gather some basic weather information to calculate the proper size for gutters and downspouts for a house. 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.

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. Determine the size of your downspout. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.

Box gutter with rain water head at end of box 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. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. 15 m is a practical maximum gutter length to be served by a downspout.

Then use the information below to see what size gutter you need. 5 inch 5 520 square feet. Downspout sizes must not exceed the bottom width of the 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. An inch of rain is not much but it if falls in half an hour it could flood a gutter. The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. Please lower the maximum spacing between downspouts to see this effect.

There is no limit to downpipe size or eaves gutter size. 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. Match your downspouts to the gutter size you chose in step 7. Total roof area also affects runoff.

5 inch 5 520 square feet. To limit the effects of thermal expansion in gutters 50 ft. 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.