Applicability   The greatest potential for the application of green roofs lies in urban or suburban development, for a number of reasons: higher impervious surface area, poor air quality, poor sound insulation, expensive temperature regulation, and loss of wildlife habitat. Green roofs are touted for their ability to reduce impervious surface area, as they retain 50-70 percent of the storm water that they receive. Thus, the most beneficial applications of green roof technology are on large buildings, malls, corporate campuses, industrial warehouses - any structure which normally generates substantial runoff.       Figure 1. Chart showing water runoff rates over time using a green roof compared to traditional impervious roof.       Even small roofs in urban areas produce environmental, economic, and health benefits. Research is currently underway exploring the use of a roof garden for food production (see www.peck.ca and search the research category for details).       Architects and landscape architects should consider every building as a candidate for a green roof. The more roofs covered by vegetation, the greater the cumulative effect. Lightweight extensive roofs can be retrofitted to most existing roofs with a pitch up to 20 degrees. Intensive rooftop gardens can be a valuable amenity for new construction.