Milwaukee Public Library's "green roof"

"Milwaukee Public Library is working with the City's Office of Environmental Sustainability and other public and private agencies to create an environmentally friendly, energy efficient structure that can be enjoyed for years to come. The Library is adding solar electric panels to the green roof which will generate about 36,000 kilowatt hours per year. A green roof uses a watertight membrane, protective layer, insulation, a filter layer, soil and vegetation to create a roof system. This project will provide both short- and long-term benefits for Milwaukee residents. In the short-term, replacing 30,000 square feet of traditional non-porous roof with a vegetative system will reduce polluted stormwater runoff, urban heat islands and improve air quality. Long-term, Milwaukee will benefit from reduced costs for water treatment systems and infrastructure"