A penthouse above the Seattle waterfront offers both privacy and open spaces

The word penthouse brings to mind luxe furnishings and exclusive New York neighborhoods. But its dictionary definition is simply "an apartment or dwelling on the roof of a building, usually set back from the outer walls." Tom Bayley's unique little abode-in-the-sky so fits that definition that he might have studied it before building his 800-square-foot pop-up penthouse atop a commercial building on the Ballard waterfront.

"We couldn't not build it with this view," says Miller-Hull Partnership architect Scott Wolf of this most unusual project. His sleek design takes full advantage of the 220-degree view of water, mountains and industrial waterfront. The boxlike unit is wrapped in glass, with oversized windows and doors so unobtrusive it's like living outdoors. And because the penthouse is up there in the sky all by itself on more than an acre of roof, privacy is no problem.

"I always wanted to do something like this," says Bayley, intrigued by the idea of topping an older building with a new penthouse. His self-described "novel of a long lease" grants him roof and air space for the building, made easier because his family owns the building. He was willing to invest what it cost to reinforce the 40-year-old structure and gain access to the roof. Now he wakes up to a view of working ships coming and going that's as immediate and graphic as an oversized children's picture book.

The city building code allows for 800 square feet of indoor "warm space," or a caretaker's cottage, on top of commercial buildings. Bayley first toyed with the idea of a prefab unit that could be lifted onto the roof, and perhaps taken down later. But it turned out to be easier to hire a contractor to build the unit in place. It fell to Wolf to plan the unit with the notion it could always be lifted off.

Wolf's design is airy, open and spacious, despite its minimal footprint. Nine-foot-high ceilings, an abundance of natural light flowing in and a minimum of colors and materials make the space seem larger than it really is. Scott organized the home's functions along a spine-like bookcase wall, which runs the length of the building, from the kitchen through the living room, ending in the master bedroom. It holds cookbooks and a microwave at one end, a television in the middle, and books along its entire length.

Outdoor decking floats the unit slightly above the roof on its own island of cedar planks. And it provides another 400 square feet of living space, although sometimes Bayley is driven inside by wind or glaring sun off the water. He's mitigated the arid quality of the roof by planting dozens of conifers in galvanized feed troughs and metal garbage cans. This urban forest will grow up to provide a sense of scale and shelter to the exposed rooftop. He selected tough, seaside plants like cistus, arbutus and barberries to fill the planters that run the length of the deck.

What does Bayley like best about his perch above the Lake Washington Ship Canal, a waterway author Jonathan Raban calls Seattle's Main Street? He's happy to muse:

"I'd say it's the odd dichotomy of complete privacy on an acre and a half of roof, next to the busiest waterway, with the Olympics in the distance."

Valerie Easton is a Seattle freelance writer and author of "A Pattern Garden." Her e-mail address is valeaston@comcast.net. Benjamin Benschneider is a Pacific Northwest magazine staff photographer.