Calculate Rainwater 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 rainwater gutter size.

To limit the effects of thermal expansion in gutters 50 ft. Rainwater calculations on face value guttering installation is a piece of cake but it is amazing how many installers get it wrong. If a roof s various drainage areas call for different size gutters go for the biggest one k style. Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.

15 m is a practical maximum gutter length to be served by a downspout. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Refer to the gutter packaging or specification for the recommended downspout size. Then use the chart below to see what size gutter you need.

Calculating effective roof areas where gutter angles are installed effect of angles if a length of eaves gutter includes an angle. 5 inch 5 520 square feet. Determine the size of your downspout. Downspout sizes must not exceed the bottom width of the gutter.

The area that your chosen guttering system can cope with. There are two things you need to know. The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. 5 inch 5 520 square feet.

As most roofs are not flat this needs to be calculated we ll show you a simple way. If a roof s various drainage areas call for different size gutters go for the biggest one k style. The total rainfall and how rapidly it falls will affect the runoff from the roof. Total roof area also affects runoff.

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. The effective roof area that will collect the rain which will need to be removed by the guttering. 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.

Box gutter with rain water head at end of box gutter. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist. Match your downspouts to the gutter size you chose in step 7. Then use the information below to see what size gutter you need.

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. This can be calculated by using the following formula see diagram below. Gather some basic weather information to calculate the proper size for gutters and downspouts for a house.