To create a green roof, consult a structural engineer for advice on modifications needed to support the weight of a green roof. Select plants that are drought and deluge resistant. Choose plants appropriate for a green roof and check on the maintenance they require. Choose between a modular system or regular soil installation, and place the plants in their spot. Roof modifications and green roof installation involve complex work that should be performed by professionals.
The roof pitch must be at least 1/4 inch per foot of run to let water flow towards the gutters, even when dealing with flat roofs. Traditional roofs support up to 20 pounds of pressure per square foot. Green roofs add an additional load of 30 pounds per square foot. Have a structural engineer modify the roof to support the extra load and to protect it from water and root growths by installing waterproofing and a rubber roofing membrane.
Install a lattice when applying the soil directly onto the protective membranes of a sloped roof to prevent the soil from sliding. Flat roofs don't require a lattice. Plant shoots and seedlings instead of seeds.
Modular green roof systems consist of 1 by 2-foot plastic trays with plants grown four months in advance. The modules are installed in rows, starting at the lowest part of the roof and moving upward. The modules come with soil elevators that are removed once the modules are in place. This creates a uniform look and allows water and nutrient sharing between modules.
Maintenance varies depending of the type of plants chosen. Hardy sedums such as the tricolor Sedum spurium are the best choice for green roofs because they are low maintenance, drought-resistant and produce colorful flowers.