Demand for home green roofs has increased over the past decade. Fred Rich planted a lush garden on his Manhattan terrace; the Whitcombs created a green wall with recessed containers for 600 plants. Photo: Dorothy Hong for The Wall Street Journal.

Thirty-five stories above New York Harbor,

Fred Rich

can stroll through his groves of Japanese maple, spruce and pine trees or sit under a pergola hung with grape vines, where wild strawberries and thyme grow between the paving stones. There is a hidden alpine garden, an orchard of plum, peach and heirloom apple trees, and espaliered pear trees growing on copper screens.

“There is always something in bloom,” said Mr. Rich, who will be dining on fresh arugula, spinach and radishes from his vegetable beds this week. “I do my yoga in the morning and the birds sit there and watch.”

With landscape architect

Mark Morrison

and a team of engineers, fabricators and organic farmers, Mr. Rich has created a 2,000-square-foot garden irrigated with recycled building water on the rooftop of his $4.8 million penthouse. Mr. Rich, a 57-year-old partner at the Sullivan Cromwell law firm, declined to say what he spent on his rooftop retreat, which has views of the Statue of Liberty and Governors Island.

At its most basic, a green roof consists of a carpet of hard-to-kill plants in a thin layer of soil. Luxury homeowners, however, are opting for bespoke greenscapes as carefully curated—and sometimes as costly—as art collections. With the right design, these eco-chic gardens also add insulation, absorb storm water runoff and deflect heat from the sun.

Urban Gardening Taken to New Heights

David and Henrie Whitcomb’s vertical garden redeemed a chunk of unusable space on their 2,500-square-foot wraparound terrace in New York’s Greenwich Village.
Dorothy Hong for The Wall Street Journal

Creating the natural look hundreds of feet above the sidewalk demands intricate engineering, sophisticated waterproofing and irrigation systems, custom-designed soil, and occasionally, a crane.

A block in Manhattan’s Chelsea neighborhood is scheduled to be closed to pedestrian traffic later in June while a 150-foot crane lifts 13 species of mature trees onto the roof of

Jean-Laurent Casanova’s

duplex apartment. The big lift is part of a two-year, $200,000 project to create an 1,100-square-foot arboretum reminiscent of the Southern Alps, Normandy and Corsica.

“I love trees. I really want to have shade—almost to have a little forest on both sides of the roof,” said Dr. Casanova, a 50-year-old pediatrician and research scientist from Paris who is also a professor at Rockefeller University. Designed by

Jacob Lange

of Christian Duvernois Landscape, his forest will be set in an undulating landscape of meadow grasses, perennials and creeping thyme, crisscrossed with walking paths.

Michael Gerstner

created a dense meadow-scape on the roof of his Tribeca penthouse, inspired by New York City’s High Line elevated park. “I like nature and the presence of nature—I don’t like a sterile wood deck,” said Mr. Gerstner, 39, who works in investments. He bought the duplex in a converted 19th-century industrial building in 2011 for $3.1 million, according to city records, and spent two years remodeling it to “bring the outside in,” at a cost he declined to disclose.

Once a caviar warehouse cooled by giant blocks of ice, the structure was strong enough to support 15,000 pounds of plant and soil. Architect

Andrew Franz

cut out part of the sloping roof to install a large retractable skylight—the roof garden’s access point. Because of the roof’s severe pitch, a scaffold structure was built to support the plants and trees, which include birch, ginkgo and a black pine Mr. Gerstner prizes for its “sculptural” qualities. Juniper bushes, lavender, bright yellow yarrow and Scotch broom frame an ipe-wood deck. Although the plants have been selected for their hardiness in excessive sun and wind, they still require tending. A gardener makes regular visits to the 1,000-square-foot space, and a drip-irrigation system delivers measured amounts of water to different plant zones.

Among its practical benefits, the meadow cools the duplex in the summer and insulates it during the winter, enabling Mr. Gerstner to leave the building’s original wood beams exposed. It has also saved him the cost of a summer rental in the Hamptons.

Residential demand for planted rooftops has grown between 15% to 20% each year over the past decade, according to

Ed Jarger,

general sales and marketing manager for American Hydrotech, a manufacturer of green-roofing systems whose clients include New York’s Lincoln Center and the California Academy of Sciences in San Francisco. The cost of installing one of his company’s garden-roof assemblies—a watertight rubberized asphalt membrane overlaid with a root barrier, insulation, a drainage and water-retention layer, and an engineered growing medium (“We don’t like to call it dirt.”) can range between $30 to $60 a square foot, or more. “More high-end single-family homes are putting green roofs on sloped structures, where the roof becomes part of the ground,” said Mr. Jarger.

For

Ken Hilgendorf,

an architect and builder in Los Angeles, a sloped green roof was the solution to a complicated renovation of his home in the city’s Westwood section. Set on a hill 30 feet above street level, “it was the lowest-cost house in the neighborhood, because the hill was so big,” said Mr. Hilgendorf, who paid about $600,000 for it in 1999.

“
I like nature and the presence of nature—I don’t like a sterile wood deck.
”

—Homeowner Michael Gerstner

During a four-year renovation, he built a 75-foot-long garage at the foot of the property, then spent $54,000 on a green roof and landscaping designed by

Stephen Billings

of Pamela Burton and Co. A massive earthwork sculpted from 150 cubic feet of “fluffy” custom-crafted soil, the garage roof is planted with a sycamore tree, ornamental grasses, and a bright green hillock of no-mow grass—a fescue mix that tolerates excessive heat and drought conditions. A thick hedgerow at the lip of the roof prevents anyone from tumbling off the lawn and onto the sidewalk.

“It’s like you’re in a tree fort,” said Mr. Hilgendorf.

In New York City, the impact of a green roof on an apartment’s resale value is a matter of debate. “Every square foot that you sacrifice for landscaping as opposed to usable space is going to make the terrace less valuable,” said Michael Vargas, CEO of Manhattan-based Vanderbilt Appraisal Co.

David and

Henrie Whitcomb’s

vertical garden redeemed a chunk of unusable space on their 2,500-square-foot wraparound terrace in New York’s Greenwich Village. Their penthouse, which public records show was purchased for $8.7 million in 2007, had “a great big 15-foot-high, 15-foot-wide ugly tan brick wall” that ruined the view from the master bedroom, said Mr. Whitcomb, who founded Automated Trading Desk, one of the first high-frequency trading firms.

The Whitcombs, who own a second home in Hawaii, couldn’t tear down the wall: It is the 1928 building’s chimney. So they transformed the eyesore into the centerpiece of their terrace garden, which also features a grove of Japanese maple, gray birch and serviceberry trees, and an evergreen that can be pushed on a built-in track to a prime spot at their living room window at Christmas.

During the 26-month remodeling project, the Whitcombs’ architect,

John Tinmouth,

and landscape architect, Linda Pollak, designed a wall of panels with a water feature and recessed slots for 600 plants to bracket to the chimney. Future Green Studio, a New York-based firm specializing in green roofs and green walls, embedded the panels with ornamental grasses and trailing plants in shades of green, silver and purple. The plants are watered by a drip irrigation system.

“I’m guessing that it might have been, by itself, a half-million dollar installation,” said Mr. Whitcomb. “By high summer, it looked absolutely wonderful. Then began the cold weather, and the wind blowing off the steppes of New Jersey. By April, the wind had taken off almost all the plant material and most of the soil.”

Now, the wall must be replanted each spring, “based on what plants will survive there, and what plants will hold the soil,” said

Emma Decaires,

the Whitcombs’ horticulturalist.

Luxury developers are responding to city dwellers’ hunger for free-form green spaces. Completed last summer, DDG Partners’ new 37-unit condo building in Manhattan’s Meatpacking district gives a nod to the abandoned, overgrown buildings that once stood nearby; its marquee is planted with a lush tangle of trees, shrubs and flowering plants that spill through amoeba-shaped cutouts. A two-bedroom apartment there is listed for $4.5 million.

The company’s 42-year-old CEO,

Joe McMillan,

lives in a ground-floor apartment at another DDG building in NoHo, where plants and vines creep across the bluestone facade from irrigated window boxes. Although Mr. McMillan’s master and guest bedrooms are at street level, they are shielded from view by the living woodland tableaux planted in the recessed windows: a rock garden overgrown with ferns; witch hazel, yew and cypress trees growing out of thick plantings of grape-holly.

“When you look out the window, it’s like a framed picture,” Mr. McMillan said. “There’s a certain sense of calm that you get from having green.”