Green roofs are gaining acceptance in dozens of countries, joining other forms of green infrastructure that are being used to mitigate environmental problems of urban centers.
For example, vegetated roofs “are very good at managing stormwater. Most extensively planted green roofs will hold the first inch of rainfall and slow any additional rainfall, thus reducing peak flows and lowering the stress on combined sewer overflows,” says Steven Peck, founder and president of Green Roofs for Healthy Cities (GRHC).
Many cities throughout the U.S. and Europe have green-roof mandates or incentives in place. Stuttgart, Germany, requires green roofs on all new flat-roofed industrial buildings. In 2007, Pittsburgh enacted an law establishing stormwater volume reduction standards for properties greater than 10,000 sq ft, including on-site retention of the first inch of rainfall through any combination of infiltration, evapotranspiration and rainwater harvesting. Portland, Ore., requires new city-owned buildings and existing buildings in need of a roof replacement to install a green roof on at least 70% of the roof area.
Green roofs trace their origins back several centuries, to sod roofs on homes and barns in Scandinavia—or even further, if we consider the Hanging Gardens of Babylon. But modern green roofs, involving manufactured layers of growing medium and vegetation, developed in Germany in the 1960s. And Germany is believed to be the country where green roofs are most popular, with about 10% of the roofs “greened,” encouraged by a system of government grants to property owners.
Check out the rest of the article and a slideshow of the 10 largest greenroofs in the world here.