How to Grass a Roof

Have a structural engineer evaluate your roof to determine if it will support the soil and drainage system necessary to grow grass on your roof. The engineer will study blueprints and inspect the house. Grass roofs exerts a load of 15 to 50 lbs. per square foot, according to the University of Wisconsin's Great Lakes Water Institute. Your roof must be free of leaks and structural damage, must have access to water and an electrical supply and must receive enough sun to grow grass. You may need to upgrade your roof or add support before you install the grass.

Obtain permits from your local government. A change to a roof, such as adding grass, is a major structural alteration that requires a building permit in most places. You may have to provide your city's building department with literature educating them about the advantages or installing green roofs. Some cities, such as Chicago, Illinois or Portland, Oregon, offer financial incentives for installing green roofs.

Install a gravel bed and plastic pipes for drainage. You must drain any excess water away from the roof.

Build a wood frame deep enough to hold 1 to 6 inches of soil. Use 1-by-2 to 1-by-6 lumber and join at the corners with angle braces. The edges of the frame help keep the soil from washing out. The amount of soil you need depends on the type of grass you plant. Build multiple frames and lay paving stones between the frames to allow you to maintain your grass roof. Fill the frames with soil.

Install a drip irrigation system to supply water for your grass. You'll need to water frequently until the grass roof is well established. Then you can water only during times when you don't receive sufficient rain.

Plant a variety of grass suitable for your area. Consult your county extension agent or local university for grass varieties suitable for your climate and for growing on a roof. You want a variety that won't require mowing or a lot of maintenance.

Water and cultivate your grass roof to keep out weeds for the first six to 12 months, until the grass is well established. After that, you should only have to fertilize once or twice a year and water during extended dry periods.