What Is A Green Roof System?
Modern green roof designs include a layer of vegetation planted over a waterproofing system typically installed on top of flat roofs or a slightly sloped roof, although the green roof concept can be applied to intensive roofs of any configuration, even on walls. In general, residential green roofs are much lighter and more straightforward with a modest roof load than those on large multistory buildings, including trees, and require minimal maintenance. While records of traditional sod roofs and rooftop gardens go back to 500 B.C.E., modern green roofs started becoming common in Europe, especially Germany, over 40 years ago with the layering system used today. The basic structure of the green roof layers consists of a variety of plants, several inches of growing medium (typically different than a layer of soil), filter membrane, drainage layer that provides aeration for plant roots, waterproof/root repellant layer, roofing membrane support for plantings above, thermal insulation, vapor control layer, and structural roof support. With a wider variety of plants come improvements in biodiversity (sometimes called brown roofs), management of stormwater runoff, and improved air quality by filtering pollutants in cities. As they become more popular in the U.S., green roof symposia, green roof professional training courses, and social groups are springing up in many areas.