Green Roofs

In this Emerging Issues Commentary, J. Cullen Howe of Arnold & Porter LLP’s New York office explains the basics of green roofs and their myriad benefits. He also discusses municipal laws that require or encourage their use in certain instances, including provisions enacted in Chicago, Seattle, New York and Cincinnati. The author writes:

“A green roof is a roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. Green roof systems can be modular with drainage layers, filter cloth, and vegetation already prepared in movable, interlocking grids. Alternatively, each component of the system may be installed separately. The layers of a typical green roof, from top to bottom are: vegetation, growing medium, filter membrane, drainage layer, waterproof/root repellant layer, support panel, thermal insulation, vapor control layer, and structural support. . . .

“Green roofs have many benefits. First, they provide amenity space for building users. Second, they can increase the life span of the roof by two to three times. Third, they reduce the heating and cooling loads on a building. A study by the Florida Department of Environmental Protection and the University of Central Florida found that when a green roof was installed on a building, it resulted in an 18-43% energy savings in the summer months when compared to a conventional roof. . . . 

“Chicago is generally recognized as the city that has done the most to encourage the installation of green roofs. In keeping with its City in a Garden motto, Chicago has established an innovative program that promotes the use of rooftop gardens on top of private and public buildings to reduce energy consumption. Referred to as the Chicago Standard, the city’s program requires, among other things, a minimum 50% green roof and LEED certification for all public projects in Chicago, except community centers and schools. Community centers and schools must either have a minimum 25% green roof or LEED certification plus a minimum 10% green roof, and must also focus on indoor air quality and daylighting. The Chicago City Hall green roof is one of the earliest and most well-known examples of green roofs in the United States. It was planted in 2000 to determine the effects a green roof would have on the microclimate of the roof. The green roof contains 20,000 plants of more than 100 species, including shrubs, vines and two trees.”

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