Tasked with transforming a 93-square-foot brick boiler room, built in 1916, into a guesthouse, architect and metalworker Christi Azevedo flexed her creative muscle.

“Whether it’s 100 or 1,000 square feet, it’s about going in and looking at opportunities,” she says. In this case, she saw a chance to experiment with light, volume, and materials. The architect spent a year and a half designing and fabricating nearly everything in the structure save for the original brick walls. “I treated the interior like a custom piece of furniture,” she says. She raised the roof five feet and added a full kitchen, a bathroom, closets, and a sleeping loft, accessed via a steel ship’s ladder and a glass walkway.

“When you step inside, you don’t feel like you’re in a small space,” says Azevedo, noting that the split-level design draws the eye up through the structure, which rises to 17 feet in the tallest section. Visitors liken the interior to a tree house—an assessment that makes Azevedo proud. “We don’t want to lose the delight in architecture,” she says.