TechNote 24 Green Roof  

Green roofs consist of a layer of vegetation installed on top of a conventional roof that filters rainwater through the engineered soil media. Some stormwater is taken up and transpired by the vegetation, and the remainder discharges to the roof drain system with improved water quality. A green roof system typically includes waterproofing material, root permeable filter fabric, drainage materials, growing media, and selected landscaping. Types of green roofs include intensive and extensive, ranging from deep, heavier growing media to shallower, lighter growing media.