The growing medium is held by mesh or containers. Living walls have water trickling behind them. Our class project will be to put up a green wall in a greenhouse on campus.”

Around the world, green roofs are receiving a lot of attention. In addition to the stormwater management and thermal benefits they offer, according to Berghage, one of the hot topics for green roofs is that they provide habitat for ground-nesting birds. “And some people are even investigating growing food on roofs,” he says. “That is interesting, but it probably doesn’t have large-scale application for commercial production.”

Penn State’s green roofs have low-growing perennial plants such as sedums and grasses that spread and don’t require much maintenance. “They survive the winters— we may lose a few plants the way you do in any landscaping, but they are spreading plants and they fill in the gaps,” Berghage says. “On some of our green roofs, students plant and maintain them; on others, it’s a classroom situation where they help to monitor runoff and temperatures and do vegetative survey work.

“Penn State is definitely out in front on green roofs, and the more of these things that we build, the further out in front we get,” he adds. “We’ve made a commitment to green certification of our buildings, and that contributes to an attractive environment and a reduction of the buildings’ ecological footprints.”

Because they offer protection from temperature extremes and ultraviolet radiation, green roofs actually last at least twice as long as conventional roofs, which typically are expected to endure 17 to 20 years, Berghage notes. “A bunch of things happen with a green roof,” he says. “You provide attractive surroundings and habitat for birds and insects, and reduce stormwater runoff and airconditioning demand. No wonder they are starting to attract so much attention.”

—Jeff Mulhollem