Michigan Gets Its First Passivhaus
Designed by a Maine architectural firm, the contemporary farm has I-joist exterior walls and lots of dense-packed cellulose insulation
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 GO Logic, 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.
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 2x6 stud wall, taped Zip System sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. that serves as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., 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-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. is listed by the architects at R-63.
The wall assembly is similar to one developed by Katrin Klingenberg, the founder of Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. 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 claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. . 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 2x4 stud wall on the inside and 6 inches of expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) 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 Kneer-Sud. They are turn-tilt design, which can either swing in like a casement window or tilt in. Windows have a Solar Heat Gain Coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.5 and an average U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of 0.146.
Other energy-related features:
- Whole-house ventilation: A Zehnder Comfoair 350 energy recovery ventilator
- Heating and cooling: Two separate 12,000 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /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 heaterAn appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed. .
John Semmelhack did the energy modeling.
- Rob Yagid
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