Rainwater calculations on face value guttering installation is a piece of cake but it is amazing how many installers get it wrong.
Calculate rainwater gutter size.
Then use the information below to see what size gutter you need.
Box gutter with rain water head at end of box gutter.
As most roofs are not flat this needs to be calculated we ll show you a simple way.
Downspout sizes must not exceed the bottom width of the gutter.
Please lower the maximum spacing between downspouts to see this effect.
Total roof area also affects runoff.
The total rainfall and how rapidly it falls will affect the runoff from the roof.
Gather some basic weather information to calculate the proper size for gutters and downspouts for a house.
Calculating effective roof areas where gutter angles are installed effect of angles if a length of eaves gutter includes an angle.
If a roof s various drainage areas call for different size gutters go for the biggest one k style.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
15 m is a practical maximum gutter length to be served by a downspout.
The area that your chosen guttering system can cope with.
Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
To limit the effects of thermal expansion in gutters 50 ft.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.
The effective roof area that will collect the rain which will need to be removed by the guttering.
6 inch 7 960 square feet.
5 inch 5 520 square feet.
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.
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.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.
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 are two things you need to know.
Match your downspouts to the gutter size you chose in step 7.
The simple way to calculate gutter sizes.
Determine the size of your downspout.
This can be calculated by using the following formula see diagram below.
5 inch 5 520 square feet.
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.
