A 2,440-square foot home in Holly, Michigan, is the first in the state to be certified under the German Passivhaus standard and has been named the best energy-smart home of 2014 by Fine Homebuilding magazine.
The house was designed by Matt O’Malia and Riley Pratt of , a Belfast, Maine, architectural and construction firm, and built by Michael Klinger of Energy Wise Homes. The two-story, three-bedroom was completed in 2012 at a cost of $205 per square foot.
O’Malia describes the project in an article , while its owners, Maura and Kurt Jung, offer a wealth of detail about the project .
As described by the Jungs, the house was built in Oakland County, northwest of Detroit, in “lovely moraine uplands,” an area of oak savannas and prairie fens and marshes. “These fragile habitats have not fared well with post-settlement farming practices,” they write, “widespread development, introduction of aggressive invasive plants and animals, and explosion of deer populations.”
The Jungs set out to bring their land back to full health as well as build a high-performance house that would require only a fraction of the energy to heat as a conventionally built home. The house is designed as a contemporary interpretation of a traditional farm house.
Exterior walls are 20 inches thick
To meet the Passivhaus standard for extremely low heat energy consumption, the house is designed with above-grade exterior walls nearly 20 inches thick. From the inside, they consist of a 2×6 stud wall, taped Zip System sheathing that serves as an air barrier, vertical 11 7/8-inch I-joist cavities filled with dense-packed cellulose, 5/8-in. fiberboard, housewrap and fiber-cement lap siding over a rain screen. The total R-value is listed by the architects at R-63.
The wall assembly is similar to one developed by Katrin Klingenberg, the founder of Passive House Institute US, and discussed in detail in a blog written by GBA senior editor Martin Holladay.
The air barrier is buried inside the wall where it can’t be compromised easily, and the vapor-permeable fiberboard sheathing allows drying toward the exterior.
The architects chose to inset the windows part way into the wall, rather than place them in the same plane as the cladding. The choice seems to be aesthetic rather than performance-driven. O’Malia writes in Fine Homebuilding that placing windows this way gives exterior walls “visual depth and mass,” and that shadow lines from the windows “create punches of contrast and keep the unadorned elevations from looking bleak.”
Above-grade foundation walls are made with insulated concrete forms further insulated with dense-packed cellulose in a 2×4 stud wall on the inside and 6 inches of expanded polystyrene (EPS) rigid insulation on the outside (R-60). Below-grade foundation walls are insulated to R-37, and the slab is insulated with 8 inches of EPS (R-35).
The truss roof is insulated with 27 inches of loose-fill cellulose (R-100) in the hipped roof and 18 inches of blown-in cellulose (R-67) at the shed roofs. The air barrier is 1/2-inch Zip System sheathing fastened to the underside of the trusses.
Air tightness was tested at 0.4 air changes per hour at a pressure difference of 50 pascals, well under the Passivhaus limit of 0.6 ach50.
Windows and mechanical systems
The triple-glazed windows are the aluminum-wood AHF 115P manufactured by the German company . They are turn-tilt design, which can either swing in like a casement window or tilt in. Windows have a Solar Heat Gain Coefficient of 0.5 and an average U-factor of 0.146.
Other energy-related features:
- Whole-house ventilation: A Zehnder Comfoair 350 energy recovery ventilator
- Heating and cooling: Two separate 12,000 Btu/h Mitsubishi minisplit heat pumps with wall-mounted cassettes, one on the first floor and one on the second floor.
- Domestic hot water: Stiebel Eltron Accelera 300 heat pump water heater.
John Semmelhack did the energy modeling.