Blue Roofs

In a time where water is in short supply and drainage systems easily flood, storm water needs to be controlled, now more than ever.

“Blue Roof” refer to systems that focus on rainwater collection. By using catchment pools, rain barrels and more discreet water-hungry plantings, the goal of the roof system would be to minimize the amount of storm water that a building site sheds to the rest of the city. Blue roofs are an aid to this problem. A blue roof is a roof design that is explicitly intended to store water.

Blue roofs harnesses the efficacy of stormwater control devices. Just as it sounds, blue roofs are set on roofs. They tend to occur in long, flat roofing styles with wide gutters and a large watertight liner. Commercial roofs that typically are flat on top, are idea for blue roofs.

Stormwater Control

storm_drainBlue roofs are being implemented all across the country, but help most in urbanized areas with less space for stormwater detention. These areas can experience flooding problems that can easily become a hazard.

Blue roofs use controls atop the roof’s downspouts to regulate storm water runoff flow from the roof, preventing the downstream drainage system from flooding. Water being released from the roof can be controlled. Some storm water may be temporarily stored on the roof while the discharge can be released to a storm water harvesting or infiltration system. A portion of the water can also be released to the drainage systems at a slower more controlled rate, helping to prevent flooding.

In many circumstances, blue roofs act as a fail safe for flooding. Because the roof can better regulate the flow of storm water, when the collection systems fail, the amount of damage relies on the effectiveness of the blue roof. Constructing a blue roof flow control drainage system to a flat roof typically adds less than $1 per square foot in cost.

The Benefits

There are many benefits to blue roofs. Blue roofs require no additional land area, so they workblue-roof well in areas that need the water management the most. Blue roofs may also represent a better rooftop option where a roof cannot handle the additional weight of a green roof. They are also easy to install and maintain. Along with light-colored materials, blue roofs reduce the urban heat island effect and provide rooftop cooling, lowering a facility’s energy costs.  Blue roofs provide equivalent storm water detention as a green roof at a fraction of the cost. Although it is an additional cost, blue roofs cost considerably less than other measures.

The Reality

Although still a new concept, blue roof initiatives are beginning to pop up in bigger cities such as New York and Philadelphia. A green and blue combination roof system was recently designed for a building in New York City. Initially, there was concern about the added weight to the roof.

To limit the additional weight a tray system for both blue roof and green roof elements was used. This system allowed for easy distribution of the additional weight to spaces on the roof that could bare more. Designers are expecting, with proper maintenance, the rooftop system to outlast the life of the roof membrane, in excess of 30 years. The tray system also enables repairs, tray replacement and a change of weight distribution if needed.