Steve Mellon, Post-Gazette photos Bob Bingham, an associate professor of art at Carnegie Mellon University, checks on plants on the living roof on CMU's Hamerschlag Hall. Click photo for larger image.

High on the roof of Carnegie Mellon University's Hamerschlag Hall, Bob Bingham straddles a drift of low-growing plants blooming in shades of hot pink, purple and red. Around him, deep green sedums and feathery grasses float in a sea of gray gravel.

Bingham, an associate professor of art and a member of the university's environmental practices committee, was one of the champions of this living roof, one of three at CMU. Also known as a green roof, it tops a conventional roof and is made from succulents and other plants that can survive on nothing more than rainwater.

"It's a no-brainer if you want to save energy, if you want be environmental, if you go toward sustainability," Bingham said.

In addition to sedums and grasses, the 4,000-square-foot roof supports chives, dianthus and alyssum, all common plants known for their toughness. In midsummer, the lesser-known delosperma and maleophora steal the show with their red and cherry pink blossoms. It's one of the pleasant surprises of a green roof, these beautiful plants blooming in such formidable conditions, especially this summer.

But it was not an easy sell; the people working beneath it had to be convinced it wouldn't leak. Now, those lucky enough to have a window overlooking the new garden enjoy the view.

Of course, there's much more to living roofs than looks. Joan Blaustein is project manager of 3 Rivers Wet Weather, a nonprofit organization established by the Allegheny County Sanitary Authority to cope with sewage overflows, a problem highlighted last year when torrential rains and flooding hit the region.

Hamerschlag Hall's living roof is the first of four that the nonprofit is funding as a way to reduce stormwater runoff. Green roofs will soon sprout on the Shadyside Giant Eagle, the Terminal Buildings on the South Side and a commercial building on Eighth Avenue in Homestead.

Green roofs absorb anywhere from 10 percent to 100 percent of the rain that falls on them.

"You only have overflow when it rains," Blaustein says. "If water doesn't ever get into the pipes, you don't have the problem."

Living roofs are most commonly planted on flat roofs to reduce runoff. The first layer is a thick waterproof membrane topped by insulation. A root barrier comes next, so the roots don't damage the first two layers. On top of that is a drainage layer and then the growing medium. The medium at Hamerschlag Hall is composed mostly of tiny pieces of slate that hold water when compressed. The rest is organic material that provides nutrients for the plants, which must be chosen carefully.

"They can absorb a lot of water when there is water. When there's no water, they've got to be able to survive," Blaustein said.

The water that does pass through during heavy rainfall is filtered by the medium, an added environmental benefit. Green roofs also insulate better than conventional roofs, especially in the summer. Even though they cost more initially, they end up paying for themselves in energy savings and durability (they usually last twice as long as a conventional roof).

	Type of Delosperma growing on the living roof of Carnegie Mellon's Hamerschlag Hall. Click photo for larger image.

The two other living roofs at CMU are on Posner Hall -- a rooftop garden/art installation called Kraus Campo -- and at Mellon Institute, which has 300 2-foot-square green roof blocks on two roof sections.

The Children's Museum of Pittsburgh on the North Side also has green roof blocks that are visible through an arched bay window in the office of executive director Jane Werner. The 15 blocks of sedum form a grid and were part of the museum's recent "green" expansion. Each block has rubber feet and can be moved easily. The museum is considering creating a larger living roof in the future.

The old Gimbels Building on Sixth Avenue, Downtown, has a green roof as part of what is now the Heinz 57 center. The 12,000-square-foot roof is filled with sedum, phlox and other hardy plants, including Chrysanthemum leucanthemum, a cheery, daisy-like wildflower.

Other cities are also experimenting with living roofs. In an attempt to combat the heat gain from so many black roofs, Chicago now requires that all new or refurbished roofs include green roofs or a reflective roofing. The largest living roof in the world is on top of a Ford truck assembly plant in Dearborn, Mich. Covering more than 10 acres, it is home to 100,000 plants and countless insects and birds. It even has working beehives that produce honey.

Type of Delosperma growing on the living roof of Carnegie Mellon's Hamerschlag Hall. Click photo for larger image. Sources www.3riverswetweather.org. www.greenroofservice.com www.greenroofs.com.

Green roofs are nothing new in Europe, where sod has been a common roofing material for hundreds of years. In Germany, urban areas began adding living roofs more than 30 years ago. Now, one of every 10 flat roofs is green.

Jorg Breuning and Peter Philippi, who worked on Hamerschlag Hall's roof, designed and installed green roofs in Germany for more than 20 years before moving their company, Green Roof Service, to Maryland.

The Hamerschlag roof is accessible to the public and can be seen from various buildings and the campus green. A demonstration project, it is equipped with devices that measure how much rainwater it absorbs compared with a conventional roof next door.

Bingham imagines covering every ugly black roof with plants some day.

"Why don't we have enough foresight to think about greening them for all the environmental reasons but also for beautification?"