“Naturally Philly” is a Billy Penn column that explores the city’s wildlife and plants — both familiar and extraordinary — that thrive or struggle in our urban environment.
Updated Aug. 6
As our city has grown higher and denser, it has also grown greener. Philadelphia has embraced the global trend of green roofs.
Rooftop plantings slow the overflow of heavy rain, which reduces pollution of waterways while also reducing air pollution and energy costs. In addition to their environmental and economic advantages, green roofs add a lot to “the urban experience,” according to Charlie Miller, principal and founder of Roofmeadow.
“We’re creating habitats for people,” Miller said. “These ‘human’ green spaces.”
Roofmeadow, headquartered on the second floor of a former Art Deco movie palace on Germantown Avenue in Mt. Airy, was the first company in Philadelphia dedicated to green roof design and construction. In the late 1990s, that meant Miller had to look elsewhere for work.
The company has greened roofs in more than 20 states, including projects at the Brooklyn Botanic Garden, Chicago City Hall, Millennium Tower in Boston, Music City Center in Nashville, the Jet Propulsion Lab in Pasadena, and the Department of Interior Building in Washington D.C.
Two decades later, green roofs now grow atop buildings throughout Philadelphia, too.
Not all of them are as visible as the wondrous (and possibly fictional) Hanging Gardens of Babylon — many require an elevator ride to see or experience. But others are more obvious than you might think, and the variety of landscapes and horticulture is surprisingly plentiful.
Letting the roof ‘evolve on its own’
When Miller launched his company, then called Roofscape, 21 years ago, American green roofs were patterned after German and other European models.
They were spans of low succulents planted in 3 to 6 inches of soil, uniform green carpets of sedum that thrived in Central Europe’s temperate climate. But deeper winters and hotter summers in the Northeast U.S. were less tolerable.
The first green roof Miller installed in Philly was in 1998, on the Fencing Academy on Race Street. It was a 3,000-square-foot area planted with sedum plugs. But three-quarters of the sedum varieties disappeared, “some gradually, some suddenly” Other “volunteer” perennials started popping up, carried in by birds or the wind, Miller said.
“You fight that for a couple of years. Then you make peace with it, and you let the roof sort of evolve on its own.”
In the early 2000s, Miller’s crews began intentionally adding native meadow perennials. At first the species were planted in separate spaces, but by 2009, the company — by then called Roofmeadow to reflect the evolving plant palette — was mixing low succulents and perennials together, said director of design Laura Hansplant, a meadow plant specialist.
“We now promote very diverse plantings, with sedums being only one of the choices,” Miller said.
Roofmeadow found that the phedimus genus of sedum plants create “a sheltering environment that supports other plants. By the same token, the taller plants shade the sedums. And as a community of plants, they are stronger than either one would be on its own.”
The issue is that sedums mainly evolved in Central Asia, where they sparsely cover the barren plateaus. They don’t naturally form a thick, bright putting green, but they’re coaxed into growing that way in Central Europe, Miller explained. However, it takes a lot to maintain that look on this part of the globe — which is not optimum for a garden that’s by definition out of reach.
“Our objective, especially for thin large roofs,” Miller said, “is to be stable without a lot of fine tuning over time.”
Philadelphia’s green roofs also create oases for other forms of life.
Miller has seen killdeer — a plover with a distinctive double breastband usually found on sandbars, mudflats and fields — feeding on the low vegetation of the urban roofs. Nate Johnson, whose Roofmeadow Services construction and maintenance firm is a sister company to Miller’s, said grackles and sparrows are occasional visitors to the high-rise gardens.
Even more common are bees, “who love the plants up there,” Johnson said. And “praying mantises will practically crawl over you while you’re reading.” (That’s a good thing? To each their own…) Crickets and grasshoppers also find their way to the roofs, as well as huge earthworms.
Philly’s top green roofs
Philadelphia has matured considerably since Miller began his company two decades ago. At that time, Chicago was “the happening place” for green roof experimentation and progress. Washington D.C. is now a leader in the field, with 3 million square feet of green roofs in the district.
But restrictions on views and historic preservation limit the types of roofs used in Washington, and many projects are performance-oriented, with simple, extensive roofs, Miller noted.
The leading cities are now New York and, yep, Philadelphia, Miller said.
Among the most successful projects Miller cites are the relatively small, 2500-sq.-ft. green roof designed by DIGSAU atop the cafe at Sister Cities Park, and the huge green roof on the eighth floor of PECO’s headquarters, which covers a whopping 47,000 square feet (about the same footprint as a city supermarket).
Co-designed by Roofmeadow and Re:Vision Architecture, the PECO roof has an extensive area — aka a shallow soil layer with more uniform plantings — and an intensive section with greater depth and larger plants. You can check it out up close during monthly tours conducted by the Pennsylvania Horticultural Society. (Disclosure: The author of this column is PHS communications director.)
At the top of Miller’s list of favorites are the very accessible CIRA Green (53,180 square feet) on the nine-story CIRA Centre parking garage overlooking the Schuylkill, and the green roof at Children’s Hospital of Philadelphia (15,160 square feet).
The CIRA project, also designed by Roofmeadow with Erdy McHenry Architecture as lead architect, is somewhat unusual in that — along with grasses, perennials, ferns and vines — it includes a dozen locust and oak trees. The trees are thriving in planters, according to Miller, though they have been buffeted and bent by the wind.
The roof at the Ambulatory Care Center at CHOP includes winding paths, seating, a fountain, meadows, large shrubs and shade trees – a tranquil amenity space for patients, families and staff.
“People don’t think of it as a green roof because you can enter at street level,” Miller said, although the gardens are perched atop an eight-level underground garage. Designed by the firm Nelson Byrd Woltz with Roofmeadow as consultant, the CHOP landscape is the most intensive green project in the city, according to Miller, and is an extremely complex project in terms of how the soil (as deep as 42 inches) is integrated with foam infill and hardscaping.
By contrast, the green roof on the Drexel Lebow Business School (13,830 square feet), designed by Roofmeadow with Lager Raabe Skaffe as landscape architect, is an extensive, classic succulent-only carpet cover with sedums creating a beautiful and dramatic geometric pattern.
“When I started, there was nothing happening here,” Miller recalled. “All our big projects were in Chicago, Detroit, Kansas City, St. Louis, Seattle, Portland…” But as development investment has intensified in Philadelphia, so has the “interest in high design and international design.”
Said Miller: “Now it’s just flipped around. We couldn’t have chosen to be in a better city.”