A "green roof," a roof partially or fully covered with vegetation, is rapidly gaining popularity among green building experts because of its excellent ability to insulate buildings, increase roof life span and reduce stormwater runoff. It also improves air quality, provides wildlife habitat, and in urban areas, helps reduce the heat-island effect.
A green roof usually consists of a layer of three to six inches of soil, with an underlying drainage system and root barrier. The soil can be used to grow grass, flowers, fruits or vegetables. Research conducted in Canada demonstrated that a typical one-story building with a six-inch thick green roof could reduce heat loss by 26% and reduce heat gain by 95% compared to a traditional roof.
The green roof atop the American Society of Landscape Architects in Washington, DC
Moorestown, NJ has published a visual Installation Primer for a green roof that they installed on their Library/Town Hall municipal complex.
Green Roofs for Healthy Cities is a trade association of green roof manufacturers and supporters who are dedicated to developing the market for green roof infrastructure products and services in North America.
The American Society of Landscape Architects constructed a green roof on their own building in Washington, DC (see picture above). Their site also contains great information on the project, including a case study.
 Clark, C., et al. (2008). Green Roof Valuation: A Probabilistic Economic Analysis of Environmental Benefits. Environmental Science & Technology, 42(6), 2155-2161.
 Berardi, U., et al. (2014). State-of-the-art analysis of the environmental benefits of green roofs. Applied Energy, 115, 411-428.
 Susca, T., et al. (2011) Positive effects of vegetation: Urban Heat Island and green roofs. Environmental Pollution, 159(8-9), 2119-2126.
 Weiler, S. K., & Scholz-Barth, K. (2009). Green roof systems: A guide to the planning, design and construction of landscapes over structure. Hoboken: Wiley, 175-203
 Thurning, C. E., et al. (2010). Green Roof Plant Responses to Different Substrate Types and Depths under Various Drought Conditions. Horticulture Technology, 20(2), 395-401.
 Simmons, M. T., et al. (2008). Green roofs are not created equal: The hydrologic and thermal performance of six different extensive green roofs and reflective and non-reflective roofs in a sub-tropical climate. Urban Ecosystems, 11(4), 339-348.