Throughout the world, the popularity of "green roofs" is on the rise. ENR.com reports that green roofs are being used to mitigate various environmental problems facing urban areas, most notably, storm water management. According to the EPA, green roofs also help combat a problem known as "Heat Island Effect" by removing heat from the air through evapotranspiration. This process reduces temperatures of both the roof surface and the surrounding air, allowing the surface temperature of a green roof to be lower than the surrounding air temperature on a hot day. Other benefits of green roofs include corrosion protection, noise reduction, energy efficiency, and improved air quality. And the uses for green roofs vary widely from practical to pure entertainment. The ENR.com article notes that the largest green roof project currently underway in the United States - the Croton Water Filtration Plant in Bronx County, New York City - will include a 36,512-sq-m golf driving range.
Green Roofs for Healthy Cities, one of a number of groups advocating for the increased use of green roofs in construction, defines a green roofing system as an "extension of the existing roof which involves a high quality water proofing and root repellant system, a drainage system, filter cloth, a lightweight growing medium and plants." Green roofing systems may be modular (with drainage layers, filter cloth, and growing plants already prepared in movable, interlocking sections), or the elements of the system may be installed separately. Green roofs can be used on a wide variety of buiildings, from private residences to industrial complexes, and the vegetation sustained thereon can range from simple groundcover to tall trees.
While typically more expensive to install than a traditional roofing system, proponents say that green roofs pay for themselves in terms of increased property value, aesthetic appeal, reduced heating and cooling costs, and extended life of the roofing materials. Many cities throughout the U.S. and abroad (particularly in Europe) already promote the use of green roofs - either through mandates or incentives. And the use of green roofs is only expected to increase as green infrastructure continues to gain political support.