Newly married and expecting a child, Lauren and Josh Stegall initially talked of supplementing Josh’s bachelor pad—a one-room cabin deep in the woods of Stuart, Virginia—with a double-wide trailer. The couple, who own and operate a small pest-control business, were desperate for more room, and a mobile home seemed like the path of least resistance. But it didn’t sit well with Josh: “I wanted space to be proud of, an investment,” he recalls.

On a whim, Josh reached out to Keith Zawistowski, a classmate from the boarding school he’d attended as a teen. Josh had noticed on Facebook that Keith had become an architect, and Josh hoped he might be able to help. Keith is one half of the team at the helm of onSITE Architecture, a small practice with offices in Virginia and France, where Keith’s wife and partner, Marie, is from. Since meeting as students at Auburn University’s acclaimed Rural Studio in Newbern, Alabama, Keith and Marie have used social media to document their work.

Josh’s message mentioned the 2014 HGTV Dream Home, a retreat built for the network’s annual sweepstakes. “Because that house is relatively modern, the reference made us want to meet with Josh and Lauren,” Keith says. “Driving up their seemingly endless driveway, we had to put our car in four-wheel drive, and the GPS stopped working.” The remote setting interested them. “We thought, ‘Wow, these people could be really cool to work with,’” Keith adds.

Together, the two couples established expectations, working through the homeowners’ immediate needs and limited budget. Plans were drawn for an 800-square-foot addition, providing the growing family with crucial bedroom, bathroom, laundry, and storage spaces.

The hallmark of the addition is a gabled window wall in the master bedroom—an echo of the shape of the original house. “We knew that the vista was one of the most important things about the place for them,” Keith explains. But it was not an easy sell, especially at $20,000—one-sixth of the total budget. Ultimately, the architects were able to convince them it was worth it. “Now I could never imagine not having that window there,” Josh says.

Hand-crafted details define the streamlined interior. The walls and ceilings are lined in locally harvested maple, while the bathroom is clad in smooth concrete. “Given the very small footprint, furniture is kept to an absolute minimum,” Keith says.

It’s easy to see the extremely tight budget—which the architects met in part by serving as the general contractors—as the defining characteristic of the project, but the price tag is not something that Keith and Marie prefer to emphasize. “It’s important to us that regardless of what it costs, it’s a really good piece of architecture,” Keith says.