For more than a decade, Kas Kinkead and Marty Babcock spent vacations and weekends in a home measuring only 40 square feet. That’s because their second home was a boat, which they moored to a dock after buying an undeveloped lot on Decatur Island, Wash., in 2006.

“It was a 22-foot little power boat with an enclosed cabin, a little heater and a sleeping berth,” said Ms. Kinkead, 67, a landscape architect at Osborn Consulting. “We learned living on that little boat that we could live in a small space together.”

Ms. Babcock, left, and Ms. Kinkead had previously used a boat as their second home. Credit: Ruth Fremson/The New York Times

She and Ms. Babcock, 72, a retired nurse practitioner, were happy for many years, as they explored the area, got to know their neighbors in the San Juan Islands and admired the natural beauty of their rugged hillside lot, which they had purchased for about $200,000. The only problem was that the longer they owned their land, the more time they wanted to spend there, away from their primary home in Seattle, which was a challenge when the temperature dropped.

“We decided we could start staying in the wintertime,” Ms. Kinkead said, “but that wasn’t really tenable on the boat because the water is too cold and too rough.”

It was finally time to build something bigger, and on land. But hoping to preserve the property’s natural beauty as much as possible, they wanted only a small cabin, and to minimize damage to the landscape.

Instead of indoor hallways, the home is designed with exterior circulation spaces.  Credit: Juan Benavides

Their lot is steeply sloped, and only accessible by gravel paths designed for golf carts, which presented a challenge. “We looked at that slope and tried to imagine digging out half of it for a concrete foundation, which was just horrifying to us,” Ms. Babcock said.

“We didn’t want to deal with a lot of construction trucks hauling off dirt,” Ms. Kinkead added.

At the same time, however, they wanted a structure that was robust enough to stand the test of time. “We prefer well-made things,” Ms. Kinkead said. “I was very mindful of building a project that wasn’t going to have a life-span of 20 years. I really wanted something that mattered, that counted and that was built to last.”

Two living modules clad in black-stained cedar are tucked under a single roof. Credit: Juan Benavides

For design help, they turned to the Miller Hull Partnership, an architecture firm that had designed other homes on the island. Ms. Kinkead was familiar with the firm as the chair of the community’s design review committee.

“Rather than making a huge cut or excavation into this hillside, Kas wanted to float the building above the landscape,” said Cory Mattheis, a senior associate at Miller Hull. “Letting the landscape flow underneath it was an idea she brought forward as a landscape architect and informed how we fundamentally approached the project.”

The home appears to float among the trees. Credit: Juan Benavides

To deliver on Ms. Kinkead’s request, the firm designed a “steel exoskeleton,” Mr. Mattheis said, that rests on concrete footings. The steel structure supports a rectangular deck and flat roof that seem to float among the trees.

Under this single large roof, which holds solar panels designed to provide all the energy the home needs, the architects added two living modules: one containing a living room, dining area and simple kitchen; the other containing two compact bedrooms and a shared bathroom. Both are finished with black-stained cedar outside and natural cedar inside.

The living room is paneled in cedar and can be heated by a wood stove. Credit: Juan Benavides

There are no enclosed hallways. Moving between the modules requires a stroll on the covered deck, “so throughout the day, they’re really engaging with the site and the elements of nature,” Mr. Mattheis said. The result is a home with 868 square feet of enclosed interior space that feels much larger than it is.

The design also allows the home to change over time without requiring total replacement, Mr. Mattheis said. If Ms. Kinkead and Ms. Babcock, or a future owner, ever want to expand, or simply change the design of the living space, it would be relatively easy to build different modules on the existing platform, while retaining the steel exoskeleton.

The simple kitchen is open to the living room. Credit: Juan Benavides

Even though the building touches lightly on the earth, building it still required some changes to the landscape. Ms. Kinkead designed a gravel driveway up to the home, which provided access for contractors hauling materials during construction and now provides a way for the couple to arrive via golf cart for their visits.

Ms. Kinkead, a landscape architect, designed a gravel driveway that allows the couple to arrive via golf cart. Credit: Juan Benavides

Around the house and driveway, Ms. Kinkead also designed retaining walls made from sandbags topped with grass seed. “It’s a system that’s super stable, easy to put in and very affordable,” Ms. Kinkead said. And, now that the grass is growing over the bags, even the island’s sheep, which have taken to grazing beneath the house, barely seem to notice the change.

It took about a year and a half for construction company Kaplan Homes Unlimited to build the house, which was completed in November 2023. The cost was about $1,100 per square foot for the house and roughly $200,000 for landscape work.

The large covered porch encourages outdoor lounging. Credit: Juan Benavides

The couple’s new home is a significant upgrade from their boat. “It’s everything we wanted it to be and more,” Ms. Babcock said, adding that there’s just one problem: “Now when we go up there, we never want to leave.”