Green Roofs are, as the name implies, plantings that are placed on the roof of a building. Green Roof technology is not new. After decades of practice, space-cramped Germans have honed the practice to a fine art. Industry figures suggest that 10% of German roofs are greened. Between 1989 and 1999, German roofing companies installed nearly 350 million square feet of green roofs and the rate is increasing.



Although information about green roofs is available, installation specifics are mostly proprietary and performance data are largely anecdotal. In either case, there is little actual research information available. Much of the popular semi-technical literature is only written in German, which effectively slows its adoption by Americans.



Green Roofs have been installed in the US, in places such as Chicago City Hall, and more are planned, like Ford’s River Rouge renovation in Detroit. However, our roof conditions are substantially different than those in Germany. A roof environment in Frankfurt is quite different from one in Atlanta, or Phoenix, or Minneapolis. So, while principles can be applied, Americans need information about our specific conditions.



Plant size and selection depends on the depth of the roof overburden (growing medium) and local climate, but the plants are almost always drought tolerant. Low growing plants such as grasses, sedums, and other cactus-like plants are used where the depth is only a few inches. Where the medium depth is several feet, shrubs and even small trees can be used. Although most easily used on flat roofs, a low pitch roof can also be “greened”. Green Roofs also represent a significant niche market for horticulturists, especially propagators, who would supply plants for these roofs.