“Passive house is a certification that is the most stringent in the world. It means a house is super-insulated, with airtight construction, high R-values and very strong thermal performance from windows and doors,” says Jordan Goldman of ZeroEnergy Design, who served as the passive-house consultant and mechanical designer on the project. “This home uses approximately 90 percent less energy for heat and at least 60 to 70 percent less energy overall than a code-built home.”

The two most crucial elements of designing a passive house are orienting it to take full advantage of the low winter sun and creating a tight envelope. This side of the house faces directly south, which allows the sun to warm the home through the large windows and doors. In the summer, when the sun is higher, the overhangs and balconies shade these openings to help keep things cool.

The two flat-plate solar thermal panels on the roof heat the water. The panels usually keep the water at 140 degrees, but one of the homeowners notes that even if there is an unusual span of cloudy days, the water temperature drops to only about 100 degrees. They have a small backup electrical system to heat the water in case this happens. Because of the way the panels warm up, snow melts off them.

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Because the couple uses the house mostly on the weekends, it usually cools down to about 50 degrees Fahrenheit while they are away, because the woodstove is not in use. After they throw a few logs on the fire, it’s about 60 to 62 degrees by the time they go to bed, one of the homeowners says, and by morning, it’s 68 to 70 degrees. When they leave, he sets the backup system to be ready to kick on if the house cools down below 45 degrees, but he says it rarely does; the heat from the sun is usually enough.

The architects worked with timber-frame-construction structures by Bensonwood, a New Hampshire company that manufactures factory-built homes with a focus on sustainable materials and energy-efficient performance. The framing and panels arrive on a flatbed truck and the contractors assemble the house with a crane in a matter of days. “We made a few modifications to their panels that added some rigid insulation to make sure they would meet the strict PHIUS performance standards,” Horowitz says.

The architectural design divides the house into three sections — the steel frame around the deck, the one-floor section of the main living space and the two-story bedroom wing beyond it. The steel framing mimics the timber-frame structural system of the rest of the home.

The homeowner was familiar with the industrial fiberglass grating he chose for the balcony floors; it is used for industrial platforms in the factories he builds. Its gray color matches that of the galvanized steel framing used on the exterior.

One issue with a tight envelope is keeping the air healthy and fresh. The architects used a heat recovery ventilator (HRV) to provide continuous fresh air in the home while the homeowners are there. While there is no comingling of the inside and outside air, when the air comes in from outside, it is preheated or precooled, depending on the season, by exchanging thermal properties with the outgoing air.

“They turn the HRV down very low when they are not there,” Goldman says. “We used nontoxic materials to build the house, which keeps the indoor environmental quality as high as possible.” One such material they used was PolyWhey (made by Vermont Natural Coatings) to finish the wood.

The cabinets behind the island were once a showroom display at Poggenpohl, modified to fit the space. The carpenters at Housewright Construction completed the rest of the cabinetry as well as the custom ash staircase. Some of the walls are covered in the same local ash wood used on the floors and staircase as well.

Of course, no matter how efficient the walls are, all is lost if the windows and doors can’t perform. The high-performance triple-pane windows are from Architectural Openings.

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The ceiling is covered in prefinished maple plywood. The plywood adds a warm decorative touch, and the choice also fit the spirit of keeping things as easy and simple as possible. “Unlike with drywall, the contractors only had to go up the scaffolding once to install this,” the homeowner says. “They went up, screwed it in, and they were done.”

Dining chairs: Tolix Marais A56 armchairs; Flight recliner in leather: Design Within Reach