Green Roofs

Rooftops are one of the major sources of stormwater runoff in developed areas and thus are also a major opportunity for incorporation of green stormwater infrastructure. Simply stated, the green roof is designed to capture and hold some volume of rainfall for later removal by evaporation and transpiration, along with the slow possible release of overflows. In extremely cold climates, annual evapotranspiration may be so small as to limit the benefits of green roofs. Water quality improvement has not been an important design parameter for green roofs; however, because early green roof media formulations tended to export nutrients, the use of green roofs in certain nutrient sensitive watersheds was restricted. The two principal needs for green roof maintenance are maintain vegetation health and prevent roof drainage clogging. Increasingly, green roof food provisioning is an important reason for their use.