Jed and Asia Webber weren’t actively seeking a prefab existence when they bought property in Groton, Massachusetts—an hour away from their home base in Cambridge, where they run a restaurant group. But the modest, sturdy frame house they fell in love with had a surprisingly modular history: It’s the Dillman model, a Sears, Roebuck and Company kit house from 1928. The Webbers, who have three children, required more space than the original structure could provide at 1,400 square feet. But since the house was “so symmetrical and appropriate for its time,” Jed Webber says, “we couldn’t wrap our heads around any sort of addition that wouldn’t look like an afterthought.” Instead, they looked online to find a prefab builder who could construct a similarly sized structure on their land.

Asia Webber, an intrepid fittings and materials scout for the family’s restaurant business, happened upon LABhaus, a prefab manufacturer based in the northeastern United States. The family’s main ask was a wall of sliding doors that could open up to the yard—a holdover from their sojourn in San Francisco. “We loved the indoor-outdoor space that comes with living in California—which of course doesn’t have the winter or the bugs that we do now,” says Jed Webber. Overall, they wanted something very modern, which fit with LABhaus’s aesthetic, and a structure that they could use as an extension of living space for their family of five.

The new 1,000-square-foot addition is situated next to a swimming pool, with a terrace protected by an overhang, which, from the backyard, frames views of the original house. “Because it is such a large property,” LABhaus architect Sara-Ann Logan says, “we wanted to scatter these buildings—like throwing stones—so we created a loosely gathered compound connected by deck surfaces.” The Garapa wood deck connects the old kit house to the new pool house, which includes a small kitchen, great room, outdoor dining room, laundry room, bathroom, and den. (Given the town’s building restrictions, the den isn’t technically a bedroom since it’s lacking a closet; to compensate, the architects added an extra-large closet in the laundry.) The Webbers, along with their children—Nina, 11, Gage, eight, and Tess, six—usually eat breakfast in the new addition and continue back and forth between the two buildings all day—except for, perhaps, in the middle of a Massachusetts snowstorm.

The main design feature of the mostly-prefabricated unit was actually built onsite: a five-panel, sliding glass door corner leading from the living space onto the deck. Considering the Webbers’ modest budget, LABhaus was concerned the residents couldn’t get the kind of system they wanted for less than $50,000. So the company tapped into its network of modular manufacturers in Pennsylvania and eventually stumbled across Solar Innovations, an aluminum door and window company that typically works in the commercial sector. “They have their own engineering department,” Logan says, “and because they’re a custom manufacturer, they don’t shy away from hard projects.” LABhaus plans to keep using Solar Innovations’ product line for future projects, a tactic that costs time and money on the front end but establishes an efficient pipeline for standardizing units.

Logan points out that LABhaus’s strength as a prefab company is its ability to source go-to modular systems for doors, cabinetry, and fixtures that can be reused in multiple projects with different finishes. “As an architect, it’s fun for me to spend hours researching, but only a certain amount of the population can pay someone to do that,” Logan says. “Let’s figure out how to make beautiful design choices accessible to more people.”