A green roof requires regular irrigation until the plants have become established. Thereafter the plants need to be irrigated as and when necessary. This maintenance is determined by the type of vegetation, the depth and drainage characteristics of the soil and the prevailing atmospheric conditions. Opportunities exist for irrigation using water collected in the gutters of the roof and adjacent roofs and grey water from kitchens and bathrooms.
The ideal characteristics of the plants to be selected are that they are drought resistant and wind resistant, they small low growing, easily reproduce themselves from seed in the event that the plants die of during times of extreme heat or drought. In addition it is of advantage if they have a creeping habit so that they are easily able to fill gaps left by die back during times of moisture stress.
Depending on the roof to be greened it may need to be waterproofed, on many suitable structures this has already been done, on others it may be advisable to provide waterproofing, this can usually be combined with the need to provide a root barrier. A root barrier is to keep the roots of the more vigorous plants from damaging the waterproofing.