Green Roofs & Heat Island

The benefits of green roofs are well understood - but one often has to wonder where the data is to validate some of these claims, or more specifically, the availability of local, transferrable data that can aid in good decision-making for designers.  Building on the Sustainable Sites initiative, there is a movement to develop a framework of more rigorous study of landscape performance in order to fill these design specific knowledge gaps.  The desire for data is being met by a number of studies, including this one, via The Dirt, for a newly published report from Columbia University for evaluating the ability of Con Edison green roofs and cool roofs in the mitigation of urban heat island effects.  A summary, via The Dirt:

"A new green roof project organized by Columbia University and New York power company Con Edison adds to a growing body of research that demonstrate green roofs reduce the urban heat island effect. Using Con Edison’s training center in Long Island City, Queens, the researchers found that a layer of roof-friendly soils and plants reduce the rate of heat absorption by 84 percent in the summer, bringing down building cooling energy costs as a result."

:: Green and Cool roofs - images via Con Edison

Some additional info from the Con Edison press release:

"The “green roof,” consisting of 21,000 plants, keeps heat in the building during the winter, reducing the need for heating, and keeps heat out during the summer, reducing the need for air conditioning. The energy saving benefits of the white roof occur mainly in the summer, when the roof absorbs less heat than a dark roof, cutting down on air conditioning needs. The green and white roofs perform equally well in preventing a phenomenon scientists call “heat island effect,” according to the study, led by Stuart Gaffin, a research scientist at Columbia’s Center for Climate Systems Research. Conventional dark roofs absorb sunlight during the day and radiate heat back into the atmosphere at night, contributing to warmer urban temperatures."

More info from the press release for Con Edison, with a link to the full report - which I will report back on after a chance to peruse.