Living Roofs, Better Living
by Sara LaJeunesse

If Home & Garden Television were to air a program about new roofing technology, it might be called “Little Prairie on the House.” Green, living roofs are becoming popular on homes and city buildings around the globe because of their potential to reduce storm-water runoff and summertime temperatures, especially in urban areas.

Storm-water runoff is a problem in cities because pavement prevents the water from reaching the ground underneath. In addition, these flows often carry automobile oil, fertilizers and trash into urban watersheds. But research shows that living roofs can absorb significant amounts of the storm water they receive.

UGA graduate students Tim Carter and Roger Hilten are contributing to this growing body of research.

Carter has planted several types of low-maintenance groundcover called sedum (a perennial group of plants with succulent green leaves) on a roof near the UGA Science Library. “Sedums are easy to establish and very drought-tolerant,” Carter said. “We installed them in October 2003 and haven’t touched them since.”

In measuring storm-water runoff as part of a larger study on managing urban streams, Carter has found that the roof can reduce runoff by as much as 50 percent. His doctoral research also will include an exploration of how green roofs may filter atmospheric pollutants, including heavy metals such as copper and zinc.

Hilten, for his part, studies air temperature; he has documented reductions in green-rooftop temperature during the summer. City temperatures are often elevated because of the urban heat-island effect caused, in part, by buildings’ and pavement’s absorption and re-radiation of solar heat. Green roofs may reduce air temperatures as plants take in water through their roots and lose it through their leaves, resulting in a cooling effect.

For example, Toronto’s $1 million, public-private Green Roof Infrastructure Demonstration Project has shown roof air-temperature reductions of up to 36 degrees compared with average summer rooftop temperatures.

“Temperature reductions on the roof translate into less heat transfer into building spaces and therefore less need for air conditioning,” Hilten said.

For more information contact Tim Carter at or Roger Hilten at