Sara Furlan’s clients were elated to snag the penthouse unit in a building off the Mag Mile. Among other things, the 12th-floor residence offered some 2,700 square feet of outdoor living space, which they planned to use for grilling, entertaining, doing yoga, and exercising their dog.

“The home has a beautiful wraparound terrace and great views of Lake Michigan,” says Furlan, design director for Lake Bluff–based Mariani Landscape. “It kind of has everything.” The residence was remodeled by Morgante-Wilson Architects after the purchase, and now the indoor space reveals terrace views on three sides.

As a veteran of urban landscape design, Furlan was no stranger to the nuances of rooftop gardens—the exposure to the elements and the need to deal with the structural issues of weight limits and water drainage. She removed existing concrete pavers, stained the new ones to match the limestone detailing on the building, and placed them on a pedestal system that controls water removal.

Alas, this new arrangement revealed a problem. The rooftop was at a lower elevation than many of the surrounding buildings, including a hotel, making it feel exposed. Furlan’s goal: to create a private outdoor oasis where the owners would feel comfortable relaxing.

Furlan carefully chose and arranged plants and other items to foster a sense of seclusion. An iron pergola brings scale and intimacy to the space, for instance, and serves as a frame for fabric shades that block sun and prying eyes. A water wall flanked by plants and smoked glass panels behind a grilling station also amp up the privacy.

As for the flora, flowering honeysuckle vines form a thick web of greenery on the east pergola, while a group of Wintergreen arborvitae serves as a screen. Serviceberry bushes, with their intense fall color, create a border on the southern terrace. “You need to select plants that are a little more durable on a rooftop,” Furlan says. “They are in the blazing sun, and as you might imagine, it also gets pretty windy up there.”

Other sturdy choices included the Rozanne geranium, John Creech sedum, and Green Gem boxwood—all of which grow in a variety of zinc and aluminum pots that are lightweight, insulated, and equipped with lights and irrigation.

Another ingenious solution to the challenges of sky-high living: areas of faux grass, arranged in a pleasing pattern, reduce trips down the elevator with the dog. Furlan says the synthetic material, which can be hosed down after use, mimics the look of thatch.

In their quest for a sheltered space, the owners didn’t want to lose the specialness that characterizes a penthouse. The finished design includes strategic areas where it’s possible to drink in amazing views of Chicago. “There are a couple places where we purposely did not put a planter,” Furlan says. “We wanted guests to be able to come up to the edge and have that ‘wow’ experience.”

Buy Guide

Landscape architect Mariani Landscape, marianilandscape.com. Interior architecture and design Morgante-Wilson Architects, morgantewilson.com.