Planning for Resilience: Predicting Vegetated Roofs’ Runoff Reduction

The rate of incorporation of vegetated systems into urban buildings is on the rise. These systems represent a psychological link to the natural world that city-dwellers have left behind and a physical filter to temper the effects of head, flooding, urban noise, and pollution. The main premise behind this trend is the ability of vegetation to dampen extremes of temperature and rainfall, which will become more unpredictable as climates change. To study the rainfall retention capacity of vegetated roofs, researchers at Virginia Tech have compared the runoff volumes flowing off three different depths of modular vegetated roofing systems to those flowing off a white reflective single-ply membrane roof. Results of this study demonstrated roofing systems to those flowing off a white reflective single-ply membrane roof. Results of this study demonstrated significant reductions in runoff in all the vegetated roof samples. Relationships among variable such as average temperature, relative humidity, wind speed, solar radiation, and time between storms, and their effect on runoff reduction at the treatment platforms, were identified. Statistical analysis of the data has yielded a function relating these weather variables, with predictive capacity for future implementation of modular vegetated roofing systems. Armed with tools such as these, architects and roof consultants can better design buildings prepared to accommodate the evolving global climate.