Synopsis: Studies on living roofs have shown that they provide a number of economic, aesthetic, and environmental benefits when designed and built properly: reducing annual heating and cooling costs, extending the life of the roofing material below the soil and plants, improving air quality, reducing outside noise, and controlling storm-water runoff. Author Roxi Thoren, an assistant professor of architecture and landscape architecture at the University of Oregon, explains how the layers of a living roof work together in a system. She discusses the options for waterproofing membranes, lists three ways of insulating a living roof, and discusses soil retention and drainage on sloped roofs. A sidebar describes three ways of building a living roof with modular products.

For anyone who has fought moss growing on a shady roof, the idea of intentionally planting a living roof may seem odd, but living roofs make a lot of sense on many homes. A living roof, also referred to as a vegetative or green roof, is a layer of soil and plants installed over a waterproof roof system. There is a long-standing history of living-roof performance that should help to put skeptics at ease. For example, turf houses in Scandinavia have used thick layers of soil and grass to insulate wood-framed homes for centuries. Contemporary living roofs, developed mostly in Germany beginning in the 1970s, also have a successful history. Germany has had living-roof standards since 1995, and some living roofs there have been in service for more than 30 years. Studies on those roofs have shown that they provide a number of economic, aesthetic, and environmental benefits when designed and built properly.

The energy factor

For many, interest in living roofs is based in part on their aesthetic appeal and in part on their environmental benefits. But the decision to install a roof that…