Like green roofs _ their perpendicular counterparts _ green walls are covered in vegetation and provide the benefits of natural insulation and removal of air pollutants. PNC, which provides banking and wealth management services, estimates it will be 25 percent cooler behind the wall than the ambient summer temperatures.
Green walls also can be visually engaging.
The PNC wall features more than 15,000 ferns, sedums, brass buttons and other plants that create a swirling pattern of varying hues of green above the company's logo. They are divided among hundreds of 2-by-2-foot aluminum panels that were anchored onto the building's frame after part of the granite facade was removed.
"We think it's the right thing to do for our community, for our customers and our shareholders," said Gary Saulson, head of corporate real estate for PNC. "We wanted to add greenery to an area that didn't have any. ... We really view the green wall as public art."
Steven Peck, president of Green Roofs for Healthy Cities, a Toronto industry association, said interest in green walls is growing, though the group does not keep statistics. He estimates green roof installations have increased at about 30 percent a year over five years.
Green Living Technologies LLC, of Rochester, N.Y., designed the wall at PNC. Chief Executive George Irwin said the company also has installed walls in New York City, Los Angeles, Chicago and Seattle.
PNC bills its green wall as the largest in North America. The wall covers nearly 2,400 square feet. PNC officials declined to give a precise estimate of its cost. Irwin said that on average green walls cost about $100 to $125 a square foot.
The structure at PNC requires only 15 minutes a week of watering during peak growing season _ less in winter _ provided through the building's plumbing system. PNC has a contract with the installer to prune the plants and replace dead ones if necessary.
Joanne Westphal, a landscape architecture professor at Michigan State University and part of the school's Green Roof Research Program, said the biggest benefit to green walls is their ability to help cool buildings through shading. They also help capture rainwater and release it more slowly into the atmosphere and stormwater systems.
Green Living says also that each of the roughly 600 panels at the PNC headquarters can offset the carbon output of one person a day.
Green Living got into the market several years ago after trying to devise a solution for a customer who wanted a green roof on a steeply pitched building. The walls can also be installed inside buildings.
Irwin said green walls aren't exactly a new idea: The Romans planted grape vines along building walls, resulting, he said, in faster growing and sweeter grapes for wine. The structures are also prevalent in Europe, where modern-day green roofs first took off.
Near ground level of the building where PNC's wall is located, at 1 PNC Plaza in downtown Pittsburgh, a small panel holds some of the plants and a plaque tells passers-by about the wall.
"I think they want to believe it's real," PNC's Saulson said, "and it is."
On the Net:
Green Living Technologies: http://www.agreenroof.com
Green Roofs for Healthy Cities: http://www.greenroofs.org