Image Credit: Wolfworks Fiber-cement clapboard siding over a rainscreen gap finishes the exterior of the house. High-performance windows are located in the sheathing plane.
Image Credit: Wolfworks Windows are small on the north side, but builder Jamie Wolf chose glazing with a high solar heat gain coefficient. A covered porch and attached garage are two amenities.
Image Credit: Wolfworks South-facing windows help illuminate the living and dining areas, located on the long axis of the house.
Image Credit: Wolfworks The house has a simple shape and a simple roof form. In addition to two full stories above ground, there's ample activity and mechanical space in the lower level.
Image Credit: Wolfworks
A 3,561-sq. ft. home in Harwinton, Conn., is the state’s first certified Passivhaus and the overall winner of the 2012 Connecticut Zero Energy Challenge, a statewide design/build competition that recognizes energy-efficient building practices.
The three-bedroom house was designed and built by Wolfworks Inc., of Avon, Conn., and incorporated a variety of features to help it meet the Passivhaus standard for low energy use and low rates of air infiltration.
In addition to winning the Connecticut Zero Energy Challenge, the Harwinton house also won three of the four contest categories, including the lowest HERS index (-12), the lowest projected annual net operating cost ($64), and most affordable project ($169 per square foot).
Homeowners Diane and Paul Honig moved in last October. Some of the highlights detailed by builder Jamie Wolf:
- A double stud wall consisting of two 2×4 stud walls separated by 5 inches of rigid foam insulation (4 inches of expanded polystyrene and 1 inch of polyisocyanurate) sheathed with Zip System OSB.
- Dense-packed cellulose insulation in the walls and 24 inches of loose-fill cellulose in the roof trusses.
- Raised-heel roof trusses.
- Triple-glazed tilt-turn windows.
- Windows with a high solar heat gain coefficient on both the north- and south-facing walls.
- A photovoltaic system with a rated capacity of 10.5 kW and a homeowner-built solar domestic hot water system.
- Ducted minisplit heating and cooling and a heat-recovery ventilator.
Rigorous building practices
Wolf went to great lengths to limit air infiltration, including the use of EPDM sill seal, air-sealing tapes around windows and on sheathing seams, and a layer of taped sheathing on the bottom of the roof trusses as an air barrier. Builders were rewarded with very low air leakage: the blower-door result was 0.34 air changes per hour at 50 pascals. That’s far below the Passivhaus threshold of 0.6 ach50.
The insulation values were equally impressive: R-28 slab, R-32 foundation, R-46 walls, and an R-83 roof.
If you’re interested in learning more about the house, there are at least three good sources of information: a blog written by Diane Honig, the website for Wolfworks, which also includes a very detailed description of the project written by Wolf, and the website for the CT Zero Energy Challenge.
Wolf says the project was his first net-zero house and the first Passivhaus design that went all the way through construction (he designed a couple of Passivhaus projects earlier but they were never built). Wolf started as a house painter, then got into remodeling. Eventually he became interested in Passivhaus construction, “drank the Kool-Aid,” and became a certified Passivhaus consultant. Because of that certification, the Honigs contacted him.
The owners like the Passivhaus approach
Paul and Diane Honig weighed their options carefully before undertaking the project and considered buying and renovating as well as new construction. In the end, the Passivhaus approach held the most appeal.
“I had read about the whole concept of Passivhaus in The New York Times — I don’t know, five years ago — about a house being built in Germany, and I thought it was kind of a cool idea,” Paul said. “I liked the idea that you make an investment up front and you get paid back in three ways: you have a more comfortable place to live, you save money in reduced energy costs, and you do something good for the environment. It seemed to make a lot of sense to me.”
And as far as choosing Passivhaus certification over a less stringent but still energy-efficient design, he said, “If you’re going to do it, you might as well do it. And since we were starting from scratch I don’t think it was that much extra effort to get the house to perform to the Passivhaus standard.”
Diane was especially drawn to the indoor air quality and comfortable temperatures the design promised, in part because she grew up in New York City apartments were no one really has any control over the indoor air environment. “There are so many quality-of-life benefits to Passivhaus as well,” she says. “That was one of the things I liked about Passivhaus specifically, rather than just a ‘green’ house that lots of green aspects to it.”
The Honigs were in the house when Hurricane Sandy struck last fall, and lived through a couple of blizzards this past winter.
“The interesting thing was the quiet,” Diane says. “It was eerily quiet. Where other people told me it sounded like there was a freight train coming through their house during the hurricane, we heard little tippy-tapping of rain on the windows, occasionally. It was weird. We were looking outside watching the trees blow 10 feet in each direction and we didn’t hear a thing.”