Sharing a vacation home is a common arrangement. But sharing an architectural and conceptual experiment—as well as a linked basement, sprawling deck, and utility bills—takes more imagination, and that’s the idea architects Melana Janzen and John McMinn developed for their “cottage” near Toronto. Together with a couple of friends they built a complex, not quite one house and not quite two, that can accommodate both families at once under the shelter of a giant covered porch.

The idea of a rustic second home was attractive to the couple, who live with their kids—five-year-old Soren and two-year-old Annika—in an apartment in downtown Toronto. McMinn’s friends Graham Barker and Karina Inzunza became their partners after Barker and Inzunza got the chance to buy a rare waterfront lot on Georgian Bay, “a community of creative people, a lot of ex-hippies and artists and poets,” says Barker. Both families wanted space to entertain, McMinn and Janzen needed a bedroom for the kids, and Barker and Inzunza needed a home office and a music room.

How to fit it all? They considered building tiny neighboring cabins, but the architects looked for a more collective solution. Tight zoning regulations meant they could only have one “house,” so McMinn and Janzen stretched the definition. Their final scheme consists of a massive shed—a post-and-beam structure of Douglas fir, 20 feet high at its apex—that shelters two separate, fully insulated structures. They’re connected underground in a linked basement, where two mechanical rooms hold water heaters and an electrical system (solar panels on the roof offset power from the grid).

Aboveground, each couple has a 15-by-30-foot home with views to the outside, plus an adjoining sleeping cabin for guests. “There is an intentionality about what is separate and what is shared,” Janzen says. The expense and maintenance of the electrical systems are pooled and the outdoor spaces are common ground. Almost every day, communal lunches and dinner parties unfold on the porch, which is outfitted with swings and Japanese lanterns.

The mostly symmetrical layout of the compound, McMinn says, precludes a sense of territoriality. “The two houses and cabins have a kind of equality,” he says. That’s distinct from the typical family compound in this region and elsewhere, where small cabins usually orbit a main house. “There’s always a question,” McMinn says: “‘Are we going to have dinner on their side or on our side?’”

This comes up often, because the complex has become a year-round meeting place for the two families, who have an unusual bond: The kids call Barker and Inzunza, who is Chilean, tío and tía, and Barker says they’re “practicing for a new stage of life” as grandparents. They all come together for singalongs with guitar or mandolin, often joined by people from nearby cottages—some of whom grew up with Barker, who has summered on Georgian Bay since he was young. All four agree that an inclusive atmosphere is paramount. “Community is important to us,” Inzunza says. “Through music, through food, through entertaining, it’s important to bring people together.”

Five Tips for Designing for Community

Make it simple to maintain.

The property is partially off the grid and designed to avoid problems typical of cold climates—for example, the water lines drain into the mechanical room, which is heated all winter to keep the pipes from freezing.

Give everyone control over their space.

Although the structures share a solar panel array, the families heat their individual spaces with wood.

Create flexible space for entertaining and play.

A spacious wraparound deck accommodates a wide range of activities, from tricycle riding to communal sunset cocktails to naps on the bed swing.

Allow people to be together and apart.

The houses are oriented to the water but also to look away from each other. Insulation keeps noise at bay.

Food matters.

Each house has its own well-equipped kitchen and several dining areas, indoors and out, that foster an easy atmosphere of communal meals and impromptu gatherings.