Perched 95 feet above the streets of downtown Philadelphia, Cira Green is no ordinary public park. A sea of Kentucky bluegrass and tall fescue flows across the football field-sized roof of a 12-story parking garage wedged between two gleaming residential towers in the city’s University District.

Cira Green will help reduce flood control and storm water management costs by absorbing rain and snow. But it’s also expected to do more. The man who designed the grassy aerie, crisscrossed by walking paths, has another abiding objective.

“We can share the cities with nature in a way that is engaging and keeps us connected to who we are as human beings, and as organisms on the planet,” says Charlie Miller MS’76 MS’82, founder and president of Philadelphia-based Roofmeadow, a firm that pioneered the design of living roofs—or “green roofs”—across the United States.

“There’s a little bubble around you when you’re on a green roof,” he adds. “It gives you a sense of intimacy and security. Psychologically, the green also will be soothing to you.”

But green spaces, including parks, are under siege. The United Nations reports that 66 percent of the world’s population—compared to 54 percent now— will live in urban areas by 2030. Further, the World Health Organization says that physical inactivity due to lack of access to recreational areas accounts for 3.3 percent of global deaths.

Cira Green (which won the 2016 Philadelphia Design Award from the American Institute of Architects) and other green roof projects could be part of the solution.The roofs are commonplace in Europe, and they’ve been expanding in the U.S. since Miller launched Roofmeadow in 1997, when it became one of only two businesses of its kind in the country.

“If you can provide a dozen green roofs in a big city, and you have enough parks connected by a necklace of green areas, you can start to reap psychological benefits,” Miller says. Green spaces are also credited with, at least incrementally, reducing cities’ heat island effect, which refers to localized warmer temperatures brought on by human activities. Through evapotranspiration, plants secrete water through the pores in their leaves, cooling the air in the process. Supporters note that there are other benefits: plants also filter the air, which improves air quality by using excess carbon dioxide to produce oxygen.

Miller has designed more than 200 green roofs in 25 states—including Chicago City Hall, whose roof teems with 20,000 plants representing 150 species, many of them native to the prairie. Flora include shrubs, vines, and two trees, which provide a verdant home to a pair of beehives.

Nineteen years ago, Miller’s idea struck some as daft, eliciting blank stares as he articulated his unusual vision. But it didn’t take long to find believers. High-profile clients now include the Baltimore Convention Center, Brooklyn Botanic Garden, the Kansas City Central Library, Chicago’s O’Hare International Airport, and the Los Angeles Museum of the Holocaust.

“Charlie has pushed the boundaries of design,” says Ed Snodgrass, founder of Street, Md.-based Emory Knoll Farms, the first nursery in the country to exclusively grow and sell plants for green roofs. “He’s an innovative and creative designer who’s good at what he does because he’s always learning.” “He understands the whole assembly,” Snodgrass adds. “You’re dealing with a structure, waterproofing, draining, engineered medium, and plants. It’s a completely unique assembly compared to anything else.”

A HIGHER PURPOSE

Cira Green, Philadelphia. Photo by Albert Vecerka/ESTO

Designing living roofs wasn’t always Miller’s career ambition. After graduating from the College of William and Mary with a degree in chemistry (“It turned out I loved chemistry, but I hated being a chemist”), he enrolled in the University of Utah’s highly regarded master’s program in geology and geophysics.

His love for geology was informed by his experiences as a kid growing up in Lancaster County, Pa., where Miller thrilled to discovering limestone formations shot through with clear quartz crystals. “Things like that caught my attention,” he says. After obtaining his master’s, Miller worked as a field geologist for a year and a half with the Kennecott Copper Company and Getty Oil Minerals, both based in Salt Lake City.

But there was one problem. “When I got married, my wife said I had to have a sedentary job,” he says. “So I went back to the University of Utah and got another master’s degree, in civil engineering.”

A 1997 trip to Germany changed his career focus yet again. A German friend, a professor of environmental landscape design at the University of Pennsylvania, suggested that the pair travel to Berlin to check out the city’s Potsdamer Platz, a public square where high rises abound with green roofs. At that point the roofs had been a fixture in the city’s urban landscape for two decades.

“I could see that not only was the business potential to do something like this great, but you also could do it on such a scale that you could change the hydrology of cities and begin to reverse some of the negative effects of development,” Miller says. “I came back from my encounter extremely energized and excited, and I thought naively that if I could just explain what I had seen and what the potential was to my fellow architects and engineers and developers, that this would sweep across the United States.” Instead, he notes, “I spent a decade just trying to educate people what a green roof is. That job is not done.”

Back home in Pennsylvania, Miller wasted little time plotting his business venture. He began to mix his own soil substitute—or medium—often of light porous substances such as scoria or pumice. Laying plants and medium over a roof, after all, requires a delicate touch. Soil typically weighs 100 to 120 pounds per cubic foot; Miller’s homemade creation registers 60 to 75 pounds per cubic foot.

He designed his first green roof, a 3,000-square-foot “freebie,” atop the Fencing Academy of Philadelphia, where the husband-wife proprietors lived in a penthouse apartment. He went on to design a 6,000-square-foot roof at an alternative medicine business in Hazleton, Pa. Then came Chicago City Hall. The big-name clients have continued ever since.

A GROWING VISION

Not all of Miller’s efforts lend themselves to foot traffic. In Chicago in 2006, he designed a green roof for Walmart, which sought to control storm water runoff at one of its stores. The retail giant has since added green roofs to two other Windy City stores, and to another in Portland, Ore., where the retailer worked with Portland State University to study roof impacts on everything from heat island effects to improving overall building performance.

Green roofs are actually easier to maintain than their plant-free counterparts, says Don Moseley, Walmart’s senior manager of sustainable facilities. The roofs are planted with drought-tolerant sedum, a kind of succulent. Volunteer rose bushes sprouted at one of the Chicago stores, where a pair of geese raised their goslings amid the unlikely garden.

The roofs have also proven durable; Miller guarantees them for 20 years. “The roofing membrane itself is quite protected by the soil and vegetation,” adds Moseley, “so there’s very little or any degradation as a result of ultraviolet rays from the sun.” Green roofs, which cost from $6 to $150 per square foot, typically are overlain with four to 12 inches of medium, Miller says. “Putting four or five feet of soil on top of a building is not really a green roof,” he says. “My business is built on systems that are lightweight and thin.”

Another of Miller’s high-profile projects is Lakeside, a Brooklyn, N.Y., skating complex in the borough’s 149-year-old Prospect Park. Completed in 2013, a pair of pavilions totaling 30,000 square feet stand partly submerged in man-made hills, the roofs of which Miller topped with a mélange of trees, shrubs, perennials, and grasses.

Brooklyn Botanic Garden, New York. Photo by Albert Vecerka/ESTO

“It was a pretty big undertaking, and a pleasant surprise,” says architect Andy Kim, who designed the pavilions for award-winning Tod Williams Billie Tsien Architects. “Buildings on parkland usually don’t take risks like that; they go for safer solutions.”

“What makes Charlie really useful and kind of unique is, he’s got an artistic design sense, but he’s also got a rigorous, highly pragmatic and sophisticated technical knowledge about that kind of construction,” Kim adds. “He shares what a lot of architects who are good share—a balance of traits that includes a sense of composition and the materials—but he also has the ability to execute something that will stick around for a long time.”

A New York Times review said Lakeside “is all about the seamless integration of architecture and landscape,” calling it “subtly remarkable” and a work of contemporary architecture “that looks as if it has been here all the while, emerging from the land and integral to it.”

“You can walk up the path for the first time and not quite know where the line is between the park and the top of the building,” says Kim, who lives nearby and takes his two children to the park’s pair of skating rinks.

While thousands of green roofs now dot the United States, Miller doesn’t expect them to ever be as commonplace here as in Europe, where he says there is “an imperative to garden.”

“There’s a devotion to horticulture, and there’s more faith in Europe in general to undertake large public programs with the expectation that it’s going to create a substantial public good,” he says. “There’s much more forbearance when it comes to establishing regulations and criteria that would result in city greening laws to be visually and hydrologically transforming.”

That said, Miller helped to spawn a movement with a following all its own in America. There are now hundreds of green roof designers across the country, many of them “mom and pop” operations that take on smaller projects.

Older and wiser, Miller says he’s driven these days by a Zen-like “spiritual imperative,” a different kind of evangelism than his early days in the business. “I always used to lead with the engineering side, as in ‘We can make our cities work again. We can make them absorb water, and we can cure nuisance flooding and all sorts of things using this technology. And, oh, by the way, they’re pretty,’ ” he says.

“My company’s approach at this point is to say that you can have something on your home, on your business, in your city, or at your college that will be special and will create a unique environment that you will treasure. And it will allow you to understand what it is to be an urban dweller in a way that you may not have conceived it before.”

—Andrew Faught is a California-based freelance writer who has written widely on issues and ideas in higher education.

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