Green Roof Technology as a Stormwater Best Management Practice

Many older cities have antiquated sewer systems that are unable to accommodate increasing amounts of impervious surface runoff from urban expansion. Excess stormwater runoff often causes systems to become overwhelmed resulting in untreated raw sewage spills into lakes, streams, and rivers.Installation of green roofs addresses this problem by using plants to cover the roofs of buildings; providing runoff control as well as lowering the amount of radiant heat absorbed by the roof. Green layered roofing systems absorb water that otherwise would have become runoff and entered the sewer system, reduce runoff flow rates, delay peak flows and, possibly, improve the water quality of runoff. Quantitative information is presented on the long term performance of two different green roof technologies in terms of initial runoff retardation, maximum peak flow retardation, and quantity of flow as compared to companion control roofs located in the Pittsburgh, Pennsylvania area.