When Esta Schwartz moved into her sixth-floor condominium at the Philadelphian, the view was not its best selling point.
The condos in the front of the building look out onto the Benjamin Franklin Parkway and the Art Museum, but her balcony, at the back, offered views of a black roof studded with large air-conditioning units.
Not anymore. Last week, workers began spreading dirt atop the roof, then planting it with sedum and other greenery that will be pink in June, ocher come November. Tall grasses will hide the air handlers.
"In some ways, it's like a view out of a suburban window," she said. Perhaps a third of the building's condos now overlook, in effect, a huge lawn.
Across the city, the tops of buildings and parking lots are sprouting greenery like never before. The number of green roofs in Philadelphia has tripled since 2010, according to the Water Department, which tracks the roofs because they absorb storm-water runoff.
The city now has 111 green roofs, roughly 25 acres' worth. An additional 64 roofs are in the queue. The completed ones range from a tiny poof of greenery atop a bus stop shelter - installed at 15th and Market Streets as an attention-getter in 2011 - to one of the latest and biggest, one-acre-plus of greenery at Cira Centre South in University City.
Roof gardens are atop hospitals, office buildings, the Philadelphia Free Library, schools, and private homes. Since 2009, virtually every new building and major renovation at the University of Pennsylvania has been designed with a green roof - "an integral part of Penn's sustainability goals," said spokeswoman Heidi Wunder.
Some are even the equivalent of mini parks in the sky. One under construction atop a parking garage near the Cira Centre will be more than an acre, with trees and prime views of the city. The 2.7-acre project nearing completion at the Children's Hospital of Philadelphia is perhaps even more inviting because it's so visible - just above street level. But it's a roof all the same. The rest of the building, a parking lot, is simply underground.
"We're doing it for all the appropriate technical reasons, but it's also designed as a park for people to use," said Douglas Carney, vice president of facilities at Children's Hospital. Thus, the trees, benches, and fountains.
Charlie Miller, owner of the Philadelphia green roofs company Roofmeadows, says that two decades ago, "no one knew what a green roof was, and no one had been on one or seen one or talked about urban greening at a dinner party." Now, people have.
Though a green roof is generally much more expensive than a conventional one, there are many benefits. They can blunt heating and cooling costs. They can even lower air temperatures in surrounding urban areas. By protecting roofing material from sunlight, they can extend the life of a roof significantly.
Although the suburbs have a smattering of green roofs, they remain largely an urban phenomenon. And especially so in Philadelphia, where we can credit - or blame - the city's sewers. About 60 percent of Philadelphia's sewer system, one of the oldest in the nation, has combined sewer pipes, carrying both sewage and storm-water runoff. In heavy rains, the system was overwhelmed, and overflows into area streams carried everything from road oil to raw sewage.
The city's 25-year storm-water plan, hailed as an innovative national model, seeks to incorporate myriad smaller projects - including green roofs - at an eventual cost of about $2.4 billion. Other cities with similar problems have spent multiple times that building massive underground tunnels to hold storm water until it can be treated and released.
Current storm-water regulations require many larger construction projects to hold that first onslaught of rainwater in a storm, and in tight city spaces where a developer wants to max out the footprint, a green roof turns out to be one of the best ways to do it.
The city's new billing structure for storm water - basing the cost on the amount of impervious surface a property has - is another impetus. "An acre of pavement costs you about five grand a year," said Christopher Crockett, deputy commissioner of planning and environmental services at the Water Department, which also offers grants to help offset the cost of a green roof.
In March, City Council also doubled a tax credit for green roofs. Now, a business can get a 50 percent credit off its business income and receipts tax, capped at $100,000, for a green roof.
Another factor: Many of today's newer buildings are going for a national environmental certification, known as LEED, which gives points for green roofs.
The region's universities have not only been installing roofs, but also avidly studying them.
Among questions Drexel associate engineering professor Franco Montalto and his colleagues are pondering: Can we grow food crops, use native species (instead of desert-adapted sedum species), or create more biodiversity on green roofs in the urban Northeast? How differently do green roofs constructed on steeply sloped roofs perform? Can we adjust the design of the green roof to maximize its habitat value, such as attracting pollinators?
Villanova researchers are looking at drainage scenarios, and learning that "green roofs often have more storage capacity than we are taking advantage of," said Bridget Wadzuk, associate professor of civil and environmental engineering. The finding could lead to new drainage structures that will bring down the cost "and make green roofs an even more attractive option for storm-water management," she said.
William Foley is regional manager for ZinCo-USA, a German green roofs company that is installing the Philadelphian's roof. He noted another positive: increased property values, and not only for units with newly attractive views.
The roof's supporters pushed the value of adding to the building's reputation as a progressive and green building overall, said Joan Batory, who chairs the condo's green committee. "This is marketability we're talking about," she said. "Marketability equals money."