A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems.
Green roofs and roof-top gardens have existed for thousands of years. The Hanging Gardens of Babylon, one of the Seven Wonders of the World, used an elaborate irrigation system to create a terraced garden paradise outside of modern-day Baghdad. Northern Europeans once chose traditional sod roofs as a means of insulating houses.
Modern green roofs, which are made of a system of manufactured layers deliberately placed over roofs to support growing medium and vegetation, are a relatively new phenomenon. The modern trend started when green roofs were developed in Germany in the 1960s, and has since spread to many countries. In Germany, currently approximately 14 percent of all roof area is green
Two types of green roof exist: intensive and extensive. Intensive green roofs are essentially elevated parks. They can sustain shrubs, trees, walkways and benches with their complex structural support, irrigation, drainage and root protection layers.
Extensive green roofs are the relatively light version as found on an increasing number of natural and green built homes. They support a hearty native ground cover that requires little maintenance. Extensive green roofs usually exist solely for their environmental benefits and don’t function as accessible rooftop gardens.
Green roofs supplement traditional vegetation without disrupting urban infrastructure, they take a neglected space and make it useful. Green roofs last longer than conventional roofs, reduce energy costs with natural insulation, create peaceful retreats for people and animals, and absorb storm water, potentially lessening the need for complex and expensive drainage systems.
On a wider scale, green roofs improve air quality and help reduce the Urban Heat Island Effect. This is a condition in which city and suburban developments absorb and trap heat. Even non-accessible green roofs create stunning aerial views for surrounding neighbors and provide wildlife with a secluded, safe space. Read more on green roofs here.