Green Roof Stormwater Management

Current green roof policies tend to be prescriptive based mandating a minimum depth and or composition of green roof growing medium.

Green roof stormwater management.

Many of the vegetated roof policies and programs focus on stormwater management benefits. This course is about the different ways in which green roofs can be utilized as a stormwater best management practice and can supplement existing sewer infrastructure avoiding a number of weather related costs associated with climate change. A typical extensive green roof of 3 5 inches depth will reduce the volume of runoff by about 55 in central pennsylvania and attenuate the peak runoff rates to the level of the pre development land use. Green roofs will intercept between 15 and 90 of rooftop runoff.

Green roofs are very effective stormwater bmps. Stormwater management is arguably one of the more beneficial aspects of installing green roofing systems especially in metropolitan areas. Their major drawback is the initial cost. The plants and growing medium of a green roof absorb water that would otherwise become runoff and research indicates that peak flow rates are reduced by 50 percent to 90 percent compared to conventional roofs.

Variation in absorption rates can be as great as 50 based on differences in temperature wind evapotranspiration rates and plant uptake. Absorption of runoff into a green roof system will vary between 50 60 and is related to the type of growing medium and plant cover variability.