Green roofs can cut electric bills by 20 percent

AUSTIN, Texas (KXAN) -- Researchers at the Lady Bird Johnson Wildflower Center have completed the first study comparing the effectiveness of different types of green, vegetated roofs against traditional roofs.

The study compared green roofs created by six different manufacturers to find out how much they cooled a building's interior and how much rainwater they captured. The Lady Bird Johnston Wildflower Center is part of the University of Texas-Austin.

The lead investigator in the study, Dr. Mark Simmons, said not all green roofs are created equal, and that some do not capture rainwater and prevent it from reaching the ground.

Researchers at the Wildflower Center have been comparing temperatures from two-dozen experimental rooftops since 2006.

Based on their data, they say green roofs could reduce a building's air conditioning bill by up to 21 percent when compared to traditional black tar rooftops.

During one 91 degree day, a black top box with no air conditioning reached 129 degrees inside, compared to 97 to 100 degrees inside the green roof box.

Real-time temperatures comparing green roofs with black-and-white roofs are available here at the Wildflower Center website .