Benefits of green roofs

Water runoff management

Green roofs help reduce the problem of polluted water making its way to waterways and water treatment facilities.  Typically, rain water runs off the roofs of buildings, through dirty city streets, and into the storm drains that carry it to treatment facilities, picking up all kinds of pollutants along the way.  The plants on green roofs help slow water runoff and act as a filter, reducing the amount of pollutants that reach storm drains.  They also retain much of the water.  In summer, the plants on a green roof can retain 70-90% of the water that falls on them and between 25-40% in winter, depending on the plants and depth of growing medium.

A large Norwegian manor with a green roof. Image via Inhabitat