How to Build a Green Roof on an Existing House

Hire a qualified engineer to assess the structure of your house. A green roof is substantially heavier than a conventional roof, and not all buildings are strong enough to support one. Options include reinforcing the building and building a steel frame that supports the roof independent of the structure of the building.

Cover the roof with a waterproof membrane. If your house has a flat roof this is a fairly straightforward exercise. If your house has a pitched roof, it will need to be removed and redesigned to make it suitable for a green roof system. A waterproof membrane is a one-piece rubber cover that protects the entire roof from leakage. The absence of joints greatly reduces the risk of leakage.

Cover the waterproof membrane with soil. You can get a special soil mixture that is designed specifically to reduce the weight on a green roof. Soil is mixed with lightweight fillers that greatly reduce the total weight of the soil, allowing you to put a thicker covering of soil onto the roof without applying too much weight.

Add plants to the soil. Some green roofs have a simple mixture of wildflowers and ground cover tossed onto the soil to hold it in place. Other green roofs feature manicured gardens or food crops.