The Stone Cottage probably doesn’t seem that out of the ordinary to someone passing by. The small, compact house sits just off Stagecoach Road in Morrisville, and while it definitely has a personality all its own, when viewed from the outside it could easily pass for a typical Vermont house.

But the Stone Cottage is a passive house. That doesn’t make it any more unassertive, pliant or malleable than a typical building — it means it’s one of the most energy-efficient buildings in the state.

“We wanted to see how tight we could build, how energy-efficient we could be,” said Sean Gyllenborg, who owns the cottage with his wife, Pam Cushman. The couple lives nearby and built the small, hyper-insulated house as part of their long-term retirement plans. They aren’t retired yet, though, so for now they rent out the super-insulated, super-efficient and super cozy cottage on Airbnb. So far, guests who have rented the 1,100-square foot house since it became available in July have raved about their stay in the little energy-efficient cottage.

What’s a passive house?

According to the Chicago-based Passive House Institute US, the philosophy behind a passive house is to “maximize your gains, minimize your losses.”

In order to qualify as a passive house, a structure must meet five different standards or criteria:

  • Continuous, thick insulation throughout the entire building.
  • An airtight building envelope that prevents the infiltration of outside air and the loss of conditioned air from inside the house.
  • High-performance windows, which are usually triple-paned.
  • Some kind of balanced heat and moisture recovery ventilation.
  • Solar gain, which uses the sun’s energy for heat in the winter but also minimizes overheating in the summer.

The research behind passive houses began in the United States in the 1970s in response to the oil crisis, but interest waned soon after. German and Swedish scientists refined the theoretical ideas of their American and Canadian counterparts in the 1980s, and passive houses began popping up in Europe soon after.

The first passive house was built in the United States in 2002 when Katrin Klingenberg, who studied architecture in Germany and is the co-founder of Passive House Institute US, constructed one in Urbana, Ill. Since then, passive houses have slowly been growing in popularity.

Building a passive cottage

When Sean and Pam decided to build a small, efficient house to live in later in their lives, they weren’t actually aiming for a passive house.

“I got into building because I like to build, and I wanted to build something else,” said Gyllenborg, who owns his own construction company that specializes in energy-efficient buildings. As the building was going up, two specialists working with Gyllenborg on it — Chris West from Eco House Vermont and Jim Bradley from Caleb Contracting — let the couple know they were already on their way to building a passive house. So, they altered a few plans and designs, dove in and finished the house last October.

One of the biggest factors that make Stone Cottage so energy-efficient is the amount of insulation used. The walls and roof contain 16 inches of dense-pack cellulose insulation. There’s an extra 6 inches of foam insulation in the roof, too, and a foot of insulation below the basement floor.

The house’s triple-paned windows, which were special-ordered from a company in New York, also make a big difference. Along with keeping air in or out, the windows and the large south-facing sliding glass doors are the main source of the solar gain that heats the building. The house is laid out and nearby trees cut down so the sun heats the place up in the winter but doesn’t overheat it in the summer.

The cottage is so insulated and airtight that just the solar gain, combined with minor forces like body heat or the warmth put off by the refrigerator and dryer, is enough to keep the entire house at room temperature if it’s above freezing outside. The Stone Cottage is equipped with a small electric heater if it’s colder than that too, since this is Vermont and the mercury regularly dips below zero during the darker six months of the year.

“It’s basically an air conditioner running backwards,” Gyllenborg said. Or, it can work like a normal air conditioner in the summer.

The building’s so airtight it needs to have an air exchange system to get fresh air in and stale air out, but that helps with heating up or cooling down the house, too. The system is tied into a geo-thermal loop in the basement that ensures the air being pumped in is at room temperature.

“It’s 60 degrees when it comes in, even if it’s 20 below outside,” Gyllenborg said.

The system works so well that the tenants who lived in the Stone Cottage last winter normally only had to turn the heat on in the morning for an hour at most to keep the place warm, even during cold snaps.

“There’s very little air leakage,” Gyllenborg said. “It just doesn’t lose heat.”

It’s so well insulated and secure that when the windows and doors are closed it shuts out almost all sounds from the outside world, too.

“When the windows and doors are closed its kind of like a bomb shelter,” he said. “It’s super comfy, quiet and warm.”

It might seem like being that airtight would cause issues with mold, mildew and rot, but the materials used to build the house and the ventilation systems ensure that those don’t become problems.

With its stone base and flared cedar shingles, the outside of the Stone Cottage has a cozy, almost European look. That wasn’t entirely planned, either, at least not right at first. Initially Gyllenborg and Cushman wanted the entire building to be sheathed in stone picked from the surrounding fields, but that’s a lengthy process, even after all the stone has been picked.

“We started building it and got to where the stone is now, but it was such a long process,” Gyllenborg said. So, they got new roofing material, and used the cedar shingles intended for the roof to side the rest of the house instead. They added a flare where stone met shingle to ensure water running off the shingles would drip down away from the edge of the building.

Gyllenborg thinks the resulting look is also reminiscent of the buildings at Shelburne Farms.

The interior of the building has a European theme, too.

“It’s a modern Scandinavian look,” Gyllenborg said — it’s simple, clean and tends toward light, bright colors and openness. The layout of the building contributes, with a loft bedroom upstairs, the living room and kitchen in one large space on the ground floor, and a den that doubles as extra sleeping space in the basement. The bathroom on the ground floor and the utility room in the basement are two of the only separate spaces in the house.

“It’s only 1,100 square feet, but you don’t feel like you’re sacrificing living function,” Gyllenborg said.

As much local material as possible was used during construction, including hemlock beams, maple flooring and knotty pine for the ceiling.

Everything used on the outside of the building is low-or no-maintenance and should stand the test of time.

“It’s all built to last 100 years or longer,” Gyllenborg said.

Houses of the future

Stone Cottage is small, but passive houses don’t have to be. More and more larger houses and apartment buildings are being built or renovated as passive structures. And, it doesn’t cost that much more than building a more traditional house of the same size.

Gyllenborg estimates that constructing a passive house costs around 5 to 7 percent more than a traditional house. All told, he thinks it cost about $200 per square foot to build the Stone Cottage, which is “still on the low end of building costs.”

Plus, the low operating costs makes up for the difference pretty quickly, he said. A look at the electric bill for the house backs up that line of thinking. They only have one year to go on but those 12 months and future estimates peg the electric bill for the Stone Cottage at between $300-$400 per year.

Since they’ve opened the Stone Cottage up as an Airbnb in July the couple have been flooded with positive reviews.

“It’s been full for all but a handful of days,” Gyllenborg said.

People seem to love the open layout of the small cottage, and just how modern and energy efficient it is.

“We’ve had some people staying here just because it’s a passive house,” he said, and he sees that interest in passive houses as a sign that they will grow in popularity.

“It’s a great market,” Gyllenborg said. “This should be how houses are built in the future.”

He sees small passive houses like the Stone Cottage as ideal living quarters for young adults who are just starting out or for retirees who are downsizing their lives. He and Pam will be taking that step themselves eventually, but for now, the Stone Cottage will continue to give visitors a glimpse of the future.

Reporter • News & Citizen • Stowe Reporter • Waterbury Record

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