Constructed wet roofs combine the ideas of extensive green roofs and constructed wetlands for storm water and domestic wastewater treatment. Constructed wet roofs temporarily retain and then gradually release storm water, thereby reducing peak runoff flow rates and associated flood risk. Additionally, the treated water may be reused for irrigation or other purposes. Constructed wet roofs offer many of the same benefits as extensive green roofs, but are more physiologically active and therefore contribute to stronger positive impacts on the microclimate, air quality and biodiversity.