In Washington, I.M. Pei is most celebrated for designing the National Gallery of Art’s awe-inspiring East Wing. But the late Pritzker Prize-winning architect completed another impressive if less monumental masterpiece in the city. One of only three houses Pei designed in his entire career, the abode was commissioned in 1960 by friend and colleague William Slayton, an urban renewal administrator. With its triple-barrel, vaulted roof, the International Style dwelling piques the curiosity of passersby. Transparent elevations in front and back celebrate the landscape, while brick side walls obscure neighboring homes on the close-knit street.

Slayton and his wife lived in the modern gem for nearly 40 years. When William died, Pei delivered his eulogy on the split-level’s living room stairs.

In the early 2000s, architect Hugh Newell Jacobsen renovated the home for its second owner. This redo upgraded finishes, added a pool and removed a bedroom in the center vault to create an open study, expanding sightlines from front to back. Soon after, Slayton House was listed on the National Register of Historic Places.

A few minor improvements were made when the current owners acquired the residence in 2009. Then, more than a decade later, they decided the time had come for a sweeping change. Committed to preserving Pei’s serene zeitgeist, they needed to bring the home’s dated infrastructure into the 21st century. They also wanted to expand its 3,030-square-foot profile with a new guest room, a second office, a media room and a garage—spaces the existing scheme sorely lacked.

They entrusted the project to DC architect Robert M. Gurney. “I’ve been aware of this house since I was in architecture school,” he admits. “The opportunity to work on it was a huge honor. I just didn’t want to screw it up.”

Gurney and project architect Matt Stephens hatched a plan to strip the structure down to its brick walls, wood frame and concrete roof vaults—then recreate it, inch by inch. All new flooring, HVAC, plumbing and electrical systems were installed. The kitchen, baths and overall millwork were designed to embrace a clean, minimalist aesthetic. “The goal was to restore the home, but make it look like we did nothing,” reveals Gurney. “That was kind of the mantra for the whole project.”

As the program took shape, I.M. Pei’s original floor plans, passed down from owner to owner, were at the team’s disposal. “Even though the windows, doors and other elements are brand new, they’re exactly per Pei’s detail,” the architect notes.

From stone and white-lacquered surfaces to walnut and glass, materials were curated with Pei’s intentions in mind and applied with painstaking precision by the builder, Peterson + Collins. Take, for example, the Navona travertine flooring. The client hand-selected the slabs at a quarry near Rome, where they were dry-laid to ensure consistent patterns. “The veining runs from the end of the pool outside through the house onto the back terrace,” marvels Gurney. “It was that kind of cosmic level of detail.”

Designer Therese Baron Gurney, Robert’s wife and frequent collaborator, masterminded the interior refresh. “I balanced respect for the architect and the architecture with making the house comfortable and functional for the clients,” she says. Guided by their appreciation for mid-century modernism, the interiors blend refinished family heirlooms with a curated mix of classic, vintage and new furnishings. “We chose a soft, neutral palette for comfort and durability, supporting the needs of modern life with quiet elegance,” she adds.

To make space for additional rooms the owners desired, the architects went underground. Taking advantage of the sloping lot, a 14-foot-deep excavation below the dining room and rear terrace created space for a light-filled guest suite and a cozy media room. And behind the home, they designed a two-story structure housing an office and bath on the terrace level and a garage below.

The owners enlisted landscape architects Kevin Campion and Steve Makrinos to link the structures and elevate the exteriors. “We created a simple plant palette with subtle Japanese influences,” explains Makrinos. “The goal was to evoke calm and restraint with a limited number of species.”

Brick walls carefully matched to the main home screen the property while concrete and travertine pathways transport visitors from the front courtyard to the rear terrace and down stairs to a lower garden. “We inherited the essence of the Pei garden and tried not to veer from it too much,” Campion reflects. “But I think we sharpened it.”

The owners are elated with their reimagined home and its renewed sense of serenity. Robert Gurney attributes the project’s success to a dream team—and incredible clients. As he notes, “They understand that they’re stewards and caretakers of an iconic piece of architecture that we restored back to museum quality.”