In Astoria, Queens, amid a row of small brick houses built in 1945 with tile roofs and the occasional gable, sits a home vastly different from its neighbors.

The hints are in the bright blue louvers shading the windows and the blue checkerboard patterns embedded in the brick. The shades, as cheerful as geranium beds, move to admit or block sunlight, while the checkerboards mark places where embedded devices regulate the temperature and humidity of air passing through the walls.

Not long ago, environment-compromising air-conditioners stuck out of those spots, but they are no longer welcome here. This is a certified passive house, a recently retrofitted cuckoo in a nest of traditional Art Deco architecture. In line with a flourishing practice in home building and renovation, it uses a variety of strategies to produce consistent interior temperatures and clean-smelling air with a minimum of kilowatts.

“I liked the idea of trying to do something that was sustainable and didn’t require a lot of energy usage,” said John Keenan, the owner.

Mr. Keenan, 48, who works as a recruiter for the tech industry, bought the 1,152-square-foot rowhouse in early 2020, at a crisis point for both the city and the building. He paid what seemed like a bargain: $850,000 for the two-story residence, which had three bedrooms and a bathroom.

The location was just a few blocks from his ex-wife’s home and made it easy for their two children to go back and forth on alternate weeks. But the house hadn’t been “touched” for 30 years, Mr. Keenan said. The boiler was old, immense and dead. He could fix the original oil-heating system or put in something completely different.

At this crossroads, he approached Ruth Mandl, 41, and Bobby Johnston, 44, the married founders of a Brooklyn architecture firm called CO Adaptive. Mr. Keenan had seen an article in The New York Times about the couple’s own home, a Bedford-Stuyvesant brownstone they had modernized and made energy independent while preserving many of its decorative features.

The brownstone was the architects’ first passive house; Mr. Keenan’s was their second. But since completing the Astoria project last summer, at an estimated cost of $525 a square foot, they have made such retrofits their specialty.

“It’s an important way of extending the life of existing buildings, to make sure that they’re resilient enough to come into the next century with us,” Ms. Mandl said.

The architects, who run a design-build operation and supervise the construction of each project, start with two basic questions: What stays? And how do they responsibly manage what goes?

In the Astoria house, they kept most of the framing and flooring. When they removed the wood around the perimeter of each floor, it was to introduce an airtight membrane and a substantial amount of insulation within the walls — key features of passive houses, resulting in interior temperatures that hover from the upper 60s to the low 70s.

The membrane is also permeable to vapor, allowing moisture to travel back and forth through the walls so that indoor air never feels sticky or dry.

And just as the architects marked the places on the exterior where they replaced air-conditioners with energy recovery ventilators, or ERVs, that make heating and cooling more efficient, they repaired the “moat” they had dug around the interior perimeter with a border of red oak — the same material as the original flooring, but with the planks set diagonally. That border subtly signals the energy-saving innovations within the freshly painted walls.

Describing their process as deconstruction rather than demolition, the architects repurposed what they could, turning a couple of the joists they extracted from under the flooring, for example, into kitchen lights.

The studio worked with recycling companies to sort and repurpose waste removed from the property, including plaster, discarded windows and doors, and old plumbing fixtures and cabinetry. Outdated appliances were sent off to be disassembled with industrial magnets into reusable quantities of metal and plastic.

Ms. Mandl and Mr. Johnston were equally considerate of the materials they brought into the home. Were they manufactured with the lowest amount of carbon emissions possible (or better yet, reclaimed, as was much of the wood)? Could they be counted on not to release volatile organic compounds (a virtue of the interior paint that was used)?

For the kitchen flooring, they turned to that quaint go-to, linoleum, because of its benevolent mix of linseed oil, pine resin and sawdust, not to mention its comfort underfoot. Porcelain slabs were used for the kitchen counters and backsplash, as well as the bathroom surfaces.

Upstairs and downstairs, they preserved the original layout, and the most substantial interventions were invisible to the eye. The upper floor was gutted to the studs and the ceiling removed to accommodate hefty doses of insulation. A stack of narrow, wood-lined cubbies carved into one wall doubles as a ladder leading to a new, operable skylight.

The roof includes a solar canopy. Combined with passive-house efficiencies, including triple-glazed, tilt-and-turn windows imported from Austria, the array has reduced Mr. Keenan’s energy bill to zero dollars a year (although he still pays the electrical utility Con Edison a $25 monthly administration fee).

“How’s the soundproofing working with the doors?” Mr. Johnston asked his client about the strategy to muffle noise emanating from the bedrooms. Mr. Keenan conducted a demonstration with his pair of stocky and vocal dogs. Disappearing into one of the rooms with the animals, he could be heard commanding, “Ada, bark! Riley, bark!”

Multiple barks ensued. They were not earsplitting.

Mr. Keenan asked the architects not to “lose the Deco,” so they designed a geometric black-and-white tile pattern for the bathroom and scored horizontal grooves in all the baseboards. They also kept the original brass doorknobs, one of which flaunts a ziggurat wall plate.

They were happy to nod to the past while conspicuously saluting the future.

“Early on, John gave us a book called ‘All the Queens Houses,’” Ms. Mandl said, referring to a compilation of photos of the borough’s idiosyncratic architecture. “It emphasized for us that you can be a little different in Queens.”

In brownstone Brooklyn, with its strict preservation codes, she continued, they were discouraged from calling attention to progressive technology, even features as seemingly low-key as exterior shading. “But on this house,” Ms. Mandl said, “we were able to emphasize certain things about a passive house that maybe in other scenarios we would try to hide.”

Living Small is a biweekly column exploring what it takes to lead a simpler, more sustainable or more compact life.

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