Then use the chart below to see what size gutter you need.
Calculate rainwater gutter size.
5 inch 5 520 square feet.
There are two things you need to know.
Box gutter with rain water head at end of box gutter.
The total rainfall and how rapidly it falls will affect the runoff from the roof.
Then use the information below to see what size gutter you need.
Please lower the maximum spacing between downspouts to see this effect.
The area that your chosen guttering system can cope with.
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.
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.
The simple way to calculate gutter sizes.
15 m is a practical maximum gutter length to be served by a downspout.
The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts.
Total roof area also affects runoff.
If a roof s various drainage areas call for different size gutters go for the biggest one k style.
This can be calculated by using the following formula see diagram below.
Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.
Calculating effective roof areas where gutter angles are installed effect of angles if a length of eaves gutter includes an angle.
Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts.
Match your downspouts to the gutter size you chose in step 7.
Determine the size of your downspout.
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.
As most roofs are not flat this needs to be calculated we ll show you a simple way.
To limit the effects of thermal expansion in gutters 50 ft.
The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website.
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.
Rainwater calculations on face value guttering installation is a piece of cake but it is amazing how many installers get it wrong.
6 inch 7 960 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.
Refer to the gutter packaging or specification for the recommended downspout size.
An inch of rain is not much but it if falls in half an hour it could flood a gutter.
