Over the last 50 years, the world has seen a dramatic population shift from rural areas to urban city centers. In the United States, this change in urbanization has created large impervious surface areas, which have altered the natural processes of the earth's hydrologic cycle by increasing the quantity and flow rates of stormwater runoff impacting highly urbanized areas. In urbanized environments of the United States, sloped roofs account for a large portion of total impervious area (TIA) because single family homes, typically built with sloped roofs, represent the majority of building construction. Green roofs are considered one type of best management practice to help manage stormwater in urban areas. To date, there has been extensive research done on the stormwater performance of flat green roof systems, but limited data exists on the performance of steep sloped green roofs. If the full stormwater management potential of green roofs is going to be realized, there needs to be wide-scale adoption of green roof technology in our residential housing stock. Data from this study shows that on average, significantly larger volumes of rainwater are retained and released in delayed peak flow scenarios per rain event, when green roofing materials cover a sloped roof than when traditional roofing materials are used. Green roofing materials retained approximately 40% of cumulative rainfall and traditional roofing materials retained approximately 10% of cumulative rainfall.
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