Energy balance, water balance, and plant dynamics of a sloped, thin extensive green roof installed in the Mid-Atlantic region of the United States
Vegetated extensive green roofs can reduce peak runoff amounts during rain events, while providing numerous ecological benefits to the surrounding area. As the desire to install green roofs expands beyond roofs with little slope to those with steeper slopes, often found on residential homes, there is a need to understand how slope affects runoff. WaterShed, the University of Maryland’s winning entry in the 2011 U.S. Department of Energy Solar Decathlon competition, is used as an applied research site where studies like the runoff analysis can be completed, while helping to promote and demonstrate environmental sustainability and energy consumption efficiency. Instrumentation installed on the roof will allow high-resolution data analysis, producing hydrographs.
The research has related the sloped green roof to different moisture holding capacities throughout the different elevations, resulting in a unique energy balance for the installed green roof. The thin substrate did not significantly contribute to overall runoff reduction, with having an average 9.4% total precipitation retention, rather it helped to reduce the overall peak runoff having an elongated runoff average of 88.6 minutes after the start of a rain event, which reduces erosion and other impacts within the ecosystem downstream. This living technology’s performance over time in a new application to sloped roofs is crucial to ensure regulatory standards are met, to justify the ecological benefits, and to provide feedback for future improvements to the design and technology itself.