Garden roofs - lovely, functional, and blooming with seasonal colors - have been sprouting on a growing number of rooftops for the last several decades. Today, rooftops are blooming with new versions of these high-rise gardens. Dubbed blue roofs and purple roofs, each of these "roofs of a different color" can work with existing green roof systems to amplify the stormwater management benefits of a rooftop garden.
Taking the Blue Roof Plunge:
Blue roofs take stormwater management to the next level; this roofing type actually detains stormwater in a rooftop enclosure. "A blue roof is basically rooftop detention, utilizing some sort of void space on the roof," said Kevin Serena, Hydrotech, Central Region Technical Sales. "The goal is to detain water for 24 to 48 hours and let it slowly drain off the roof over time by restricting the water outflow utilizing a control flow drain. This cuts down on peak stormwater flow, so all the water from a given storm doesn't reach the sewer system at the same time."
In some cases, the void space for stormwater detention is placed underneath pedestal pavers. In other cases, the detention enclosure is placed underneath the plants and growing media. The Belt Line Center in Detroit has taken the blue roof plunge with a portion of the rooftop dedicated to this new system. Located on the site of Detroit's future Beltline Greenway, the Center is a rehabilitation of a vintage Albert Kahn designed building repurposed as a mixeduse facility.
