In the early days of the Covid pandemic, as some New Yorkers left the city while others hunkered down, Chris Cooper and Jennifer Hanlin saw a chance to finally buy the property they wanted: a townhouse in Cobble Hill, Brooklyn.

“Chris and I had tried to purchase a Brooklyn brownstone for years and had always been outbid by developers or buyers with full-cash offers,” said Ms. Hanlin, 55, the founder of the interior design firm Hanlin Design.

With less competition, their prospects improved. And in September 2020, when they saw a plain brick townhouse for sale that was only 12 feet wide and had none of the ornamental detailing of nearby brownstones, they became even more optimistic.

“We knew it was a weird enough property that maybe we would have a chance,” she said. “It wasn’t going to be for everybody.”

They immediately made an offer at the full asking price, just under $2 million, the seller accepted, and they closed on the property that December.

The townhouse — a slender, three-story structure built in 1899 — needed a renovation, making it perfect for the couple.

Mr. Cooper and Ms. Hanlin met as architecture students at Harvard in the 1990s, and they still enjoy few things more than tackling design problems together. They are both also deeply interested in environmentally friendly building practices, so they wanted to renovate their new home according to sustainability-focused passive house principles.

An airtight, well-insulated home would reduce energy consumption, but there would be other benefits, too, said Mr. Cooper, 57, a partner at the architecture firm Skidmore, Owings & Merrill. “There’s also the healthy environment, the fresh air, the silence.”

As they proceeded with the renovation, the couple worked with ZeroEnergy Design to wrap the basement, front and back walls and roof with an airtight membrane and thick insulation. They capped the gas line running into the home, added triple-pane windows and installed an energy recovery ventilator to provide the interior with a continuous stream of fresh air.

At the same time, the project was a chance for the couple to embrace their minimalist tendencies. “We talk about this philosophy of radical reduction,” Mr. Cooper said. “We strip down to the basics, and are very intentional and modest about what we put back in.”

Because the building had no elaborate trim to preserve, the couple tore all the interior finishes out during demolition. “We literally stripped down to the chassis of the house,” Mr. Cooper said.

With no crown molding or ceiling medallions, “the architectural detail in the house is the old joist hangers, the brick texture and whatever corrections were made to the brick,” Mr. Cooper said, including an old doorway that the original builders had used during construction but later filled in. Rather than covering these elements up, the couple painted them white.

Achieving such a raw look required some architectural sleight of hand. To leave ceiling joists exposed on the parlor level, they raised the floor on the second level, where they built their primary suite, to create a gap for hiding electrical wiring.To make the ceiling height on the lower level acceptable for Ms. Hanlin’s office, they dug the basement down by six inches.

When they realized their lot size would allow them to add 140 square feet to the home, they built a tiny two-story addition on the back that connects to Ms. Hanlin’s office and the living room and creates a deck for the primary bedroom.

Within the stripped-down shell of the building, an edited selection of art, furniture and architectural elements is given room to shine. The kitchen has a Delftware-like tiled backsplash by the artist Ann Agee that depicts a scene of Brooklyn backyards, viewed through a window.

Working with their builder, Carlo Perry of CCP Design+Build, the couple designed a sinuous, Shaker-inspired stair railing, which offers an elegant counterpoint to the rough-edged brick. It rises from the parlor level to the primary suite on the second floor, and then to two additional bedrooms on the top floor for the couple’s adult children.

The walls are adorned with the couple’s favorite artworks, including a photo of sequoia trees by Mitch Epstein and photos of flowers by Karl Blossfeldt. Furniture choices include an antique Swedish dining table under a Pinch Soren pendant lamp, which Mr. Cooper bought as a 50th birthday gift for Ms. Hanlin just as they were beginning the project.

The transformation took seven months of design and planning, and 13 months of construction, before the couple moved into their long-desired townhouse in August 2022. The renovation cost was just under $1 million.

“We’re super happy,” Ms. Hanlin said, noting that the undertaking was more enjoyable than stressful.

“The funny thing is that we actually liked the process of creating this home,” Mr. Cooper said, adding that he and Ms. Hanlin now miss working together in such a direct manner.

“That might tempt us to do it again,” he said.