The development of "green" buildings that regenerate degraded
urban environments is essential to building healthy, sustainable
communities in the 21st century. According to the U.S.
Environmental Protection Agency and Lawrence Berkeley National
Laboratories, Berkeley, Calif., rooftops represent 15 percent to 30
percent of the total land area in major cities. As such, they
present a tremendous opportunity for positive change as a key
component of green building and sustainable roof system design.
There are two basic types of green roof systems: extensive and
intensive. Extensive green roof systems range from 1 inch to 5
inches (25 mm to 127 mm) in soil depth, typically consist of mosses
and herbs, and are built primarily for their environmental and
economic benefits rather than public access. Intensive green roof
systems require at least 1 foot (0.3 m) of soil depth, elaborate
irrigation and drainage systems, and maintenance. Typically
designed to be publicly accessible, intensive green roof
applications feature trees and shrubs and often resemble city
The multiple paybacks of green roof systems are far-reaching and
involve a mix of public and private benefits, including the
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