How to calculate the size of the rain garden design:

1. Determine the area of the hard surface draining to the rain garden. In this example the length of the roof (L) times the width of the roof (W)

"L

In this example 400 ft2 will be draining to the rain garden" width="300" height="189"> L x W = Area
10 ft x 40 ft = 400 ft2 In this example 400 ft2 will be draining to the rain garden

2. Rain garden design should be 5-8% the size of the hard surface draining to them.

For 5% of hard surface - 400 ft2 x 5% = 400 ft2 x 0.05 = 20 ft2

This could be a5 ft by 4 ft rectangular bed Or a 10 ft by 2 ft rectangular bed
Or 5 ft diameter circular bed.

4. If more room is available, feel free to make the rain garden as large as you like. Be sure to follow the location guidelines on How to Build Your Own Rain Gardens page.

This information is designed to assist homeowners in building their private rain garden. Contractors, designers, and engineers are required to follow the specifications in the WV Post Construction Stormwater Guidance Manual (2012).