In urban areas, rooftop runoff can overwhelm the sewer system and contribute to water pollution. While vegetation-covered green roofing slows this runoff somewhat, its capacity is limited. For effective storm runoff control, blue roofing is a more effective option.
How a Blue Roof Works
A blue roof is designed expressly to store rainwater temporarily in order to regulate drainage from the roof. The water can then be gradually discharged into the sewer system, directed toward groundwater recharge or even used to irrigate the landscaping. This prevents the sewer system from overflowing, protecting the city from the discharge of polluted water.
A number of different devices can be used to store the water. The roofs are classified as either passive or active based on the method used for water storage. Passive systems typically use shallow pools or barrels. Blue roofs are best suited to buildings with long, flat roofs of the design often found in commercial developments.
The Future of Blue Roofing
One of the most influential blue roof pilot programs was carried out by the New York City Department of Environmental Protection (NYCDEP). The company hired to develop the roof installed risers and dams to direct rainwater into collection ponds, as well as trays capable of holding up to 2 inches of water. The tray system proved the most successful, cutting storm runoff from the roof by 45 percent.
Despite the potential benefits, storing water on a building roof poses a number of problems. The roof must be strong enough to bear the weight of standing water. Both the storage system and the roof must be sealed well to prevent leakage. It’s critical that the architect, building engineers and others involved in the building’s design collaborate closely to address potential issues. Even minor oversights can result in sudden and total collapse of the roof.
Furthermore, selling building owners on the benefits of blue roofs is a challenge because these roofs benefit the community as a whole rather than the individual building owner.