More commonly known as a "green roof" or a "living roof," vegetated protected membrane roofing is a roofing system that allows plant cultivation on its surface. A typical green roof consists of a membrane layer, a drainage layer, a soil layer and a plant layer. Although considered a new trend, sod roofs have been in use in Iceland and Scandinavia for hundreds of years, and the terraced gardens known as the Hanging Gardens of Babylon were constructed around 600 BC.
Generally, there are two types of green roof: extensive and intensive. An extensive green roof is comprised of low-height perennials and succulents and is virtually self-sustaining. An intensive green roof uses plants with foliage between 1 - 15 feet, which requires much more soil and makes it much heavier and more expensive to build and maintain.
In addition to their aesthetic and insulating benefits, green roofs have many advantages over traditional roofing systems, and a growing number of cities, including Tokyo, Zurich and Toronto, are now mandating their use in certain types of new construction projects. Green roofs reduce the temperature of the roofing membrane, which lengthens the life of the roof, improves energy efficiency and helps to decrease the heat island effect in urban areas. Green roofs also provide groundcover, filter pollutants, respirate oxygen into the air and retain water to help control storm water runoff.