Green Roofs Becoming a Great Choice for Areas With Hot Summers

Another alternative to traditional roofing materials is a rooftop garden, or "green roof." On hot summer days, the surface temperature of a vegetated rooftop can be cooler than the air temperature, whereas the surface of a traditional rooftop can be up to 90°F (50°C) warmer.  A green roof consists of vegetation and soil, or a growing medium, planted over a waterproofing membrane. Additional layers, such as a root barrier and drainage and irrigation systems may also be included.

Green roofs can be used in many applications, including industrial facilities, residences, offices, and other commercial property. In Europe, they are widely used for their stormwater management and energy savings potential, as well as their aesthetic benefits. Green roofs are an attractive roofing option that can reduce urban heat islands by providing shade and through evapotranspiration, the release of water from plants to the surrounding air. As impermeable surfaces like buildings and pavement replace open space and vegetation, green roofs can play an increasingly important role in storm water management.

During rainstorms, green roofs act as a sponge, absorbing much of the water that would otherwise run off. Researchers estimate that three to five inches of soil or growing medium absorbs 75% of rain events that are one-half inch or less. Green roofs also filter pollution from rainwater. This is achieved by the root systems' bacteria and fungi, which utilize the natural filtering processes of bioremediation and phytoremediation. As a result, the non-point source pollutants, nitrogen and phosphorus, are broken down and detoxified. This beneficial process increases over time as rooftop plants and root systems mature.