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