Green roofs, defined as vegetation-covered roof systems, are one vehicle for combating the negative effects of stormwater runoff. These vegetative roofs prevent excess stormwater runoff by retaining water and lowering peak flow rates. They also provide a myriad of other benefits, including reducing the urban heat island effect, offering better insulation, and restoring lost habitats.
Green roofs, including several on the University of Maryland campus, are most commonly found on flat buildings. However, many pre-existing buildings could also support green roofs if properly retrofitted. To fill this hole in sustainable technology, Team SO GREEN from the Gemstone Honors Program received a Sustainability Fund grant of $5,800 to design an efficient retrofit green roof system that could be appended to pre-existing sloped roofs.
The team designed and constructed a four roof module at slopes of varying degrees. The grant was used to purchase building supplies, including lumber, electrical equipment, steel, and aluminum, and also supported the purchase of the green roof substrate and sedum plants for the four modules. Then, the team collected runoff data on each of the four modules over a seven month period, and during the last three months implemented an irrigation system on one of the modules. The irrigation system was not found to increase the moisture content of the roof. However, the team concluded that since water is lost to evaporation during the recirculation process, runoff was reduced.
Gemstone Team SO GREEN wrapped up their research on sloped green roofs in December 2014 and presented their project at the Gemstone Thesis Conference in April 2015. The team’s mentor, Dr. Andrew Ristvey, will continue sloped green roof research on the four roof modules.