The First U.S. Passive House Shows That Energy Efficiency Can Be Affordable

The First U.S. Passive House Shows That Energy Efficiency Can Be Affordable

Urbana, IL

Mar 2 2009 By Rob Wotzak | 6 comments

General Specs and Team

Location: Urbana, IL
Bedrooms: 2
Bathrooms: 1
Living Space : 1200 sqf
Cost (USD/sq. ft.): $94/sqf

Completed: 2003

Builder: Edward Sindelar, Chicago
Architects: Katrin Klingenberg and Nicolas Smith, Urbana, Ill.
Energy consultant: Conservation Technologies,
Duluth, Minn.

Construction

Foundation: 4-in. slab over 14 in. 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. foam (R-56), surrounded by concrete-block frost wall covered in 6 in. of EPS foam (R-24)
Walls: vertical 12-in. I-joists (Trus Joist); 12 in. blown-in fiberglass, plus 4 in. EPS foam over exterior 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. (R-60 total)
Roof: 16-in. I-joists with vent channels above the sheathing; 16 in. of blown-in fiberglass (R-60)
Windows: triple-pane, argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor., fiberglass frames with XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. insulation (average overall 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. , .19)

Energy

Cooling: HRV (Westaflex) with 1,000-watt electric resistance heating element coupled to 8-in.-diameter, 100-ft.-long earth tube buried 6 ft. deep
Water heating: tankless electric water heater with spare conduit for future solar thermal system (Stiebel Eltron)
Annual energy use: 14.8 MMBtu

  • Superinsulation (R-56) and supertight thermal envelope
  • I-joist framing for minimal thermal bridging
  • Oriented for maximum passive solar heating and cooling
  • Triple-glazed windows positioned for winter solar gain
  • Instantaneous electric water heater
  • Prewired for future PV system

Water Efficiency

  • Plumbing lines to toilet and laundry for connection to future rainwater catchment system
  • Indoor Air Quality

    • HRV constantly exchanges air
    • Linseed oil floor finish
    • Water-based sealant on concrete floors
    • No-VOC wall paint
    • Solid wood countertops

    Green Materials and Resource Efficiency

    • Durable, recyclable galvanized-steel roof
    • CMU frost wall/on-grade slab are material- and labor-efficient design
    • Recycled tub, fixtures, and medicine cabinet
    • 100% regionally sourced wood (fir, pine, and cedar)
    • Recycled slate cladding on foundation
    • Recyclable blown-in fiberglass insulation

    Relatively Small Investments Can Add up to Big Gains with the Right Design Strategies

    With R-60 insulation and a south-facing wall punctuated by triple-glazed windows, this Passivhaus home stays comfortable during cold Illinois winters with a heater the size of a hair dryer.

    There’s actually a bit more to the story: The tall wall of glass brings in a good deal of solar heat; an exposed concrete floor absorbs and slowly releases that heat; a 100-foot-long earth tubeVentilation air intake tube, usually measuring 8 or more inches in diameter and buried 5 or more feet below grade. Earth tubes take advantage of relatively constant subterranean temperatures to pre-heat air in winter and pre-cool it in summer. In humid climates, some earth tubes develop significant amounts of condensation during the summer, potentially contributing to indoor air quality problems. warms incoming fresh air; and an HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. equipped with a 1,000-watt electric resistance heating element scavenges heat from outgoing stale air. The earth tube and HRV also help keep the home cool during warmer months.

    Following a good example
    The Smith House is the modest, comfortable home of German-born architect Katrin Klingenberg. More important, it’s an example of what she believes could and should be done with residential construction in this country. She and her late husband, Nic Smith, were inspired to build the house after visiting a Passivhaus residence in Hanover, Germany.

    Katrin and Nic were disheartened that most energy-efficient building projects fall short of the environmentally responsible benchmarks being set around the world. They hoped to create a building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. that would achieve a tenfold reduction in energy use compared to a typical home. They were guided by the standards established by the Passivhaus Institut and the Institut’s 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. Planning Package (PHPP) software.

    In 2004, not long after Katrin’s new home was completed, she had the chance to meet Dr. Wolfgang Feist, director of the Passivhaus Institut. Dr. Feist performed energy modeling that confirmed that Katrin had more than met the Passivhaus heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. standards, prompting him to include the Smith House as the first sample home in an English translation of the PHPP.

    Keeping the heat in
    The house incorporates construction details that might be considered extreme by many American builders: The insulation layer under the concrete slab — 14 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.) foam — is unusually thick; 12- and 16-inch I-joists create deep wall and roof cavities, making room for plenty of blown-in fiberglass insulation; the exterior walls and foundation are wrapped in 4 and 6 inches, respectively, of EPS; to reduce the chance of infiltration, utilities and HRV ducts enter from deep beneath the slab, and interior wiring and electrical devices (with the exception of wireless light switches) are confined to floors and interior walls.

    Sustainability extends beyond the site
    Building this house was about more than just energy savings. Katrin’s commitment to environmental responsibility demanded that she scrutinize every material that went into the home. She also considered how sustainably the components were produced and transported and what would happen to them at the end of their lifespan. Proximity to work and public transportation influenced the choice of where to build the home. Katrin planned for future reduction of her environmental impact by roughing in electric and plumbing lines for future photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) and rainwater collection systems.

    Cost: The bottom line
    At $94 per square foot, the house topped the highest averages for new construction in the region, although not by much. With Katrin's modest budget and her goal of using the home as a model for affordable housing, the cost was more than she would have liked. But she points out that this was a prototype that would likely cost less on a production scale. Besides, in her opinion, the successes in the area of sustainability, efficiency, and comfort were well worth the investment.

    Lessons Learned

    The good news is that the design worked well. The house is always very comfortable. As for the heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load., recent tests put the annual demand around 11 kWh per square meter. That's a bit above the expectation of 8 kWh, but it's a full 4 kWh below the maximum prescribed by the PassivhausA 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. Institut. Possible explanations for the discrepancy might be higher-than-assumed thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through the I-joist framing and poorer-than-expected performance of the exterior door seals.

    Tight homes can still have fresh air
    Katrin often keeps the windows closed even in warm months because the HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. and earth tubeVentilation air intake tube, usually measuring 8 or more inches in diameter and buried 5 or more feet below grade. Earth tubes take advantage of relatively constant subterranean temperatures to pre-heat air in winter and pre-cool it in summer. In humid climates, some earth tubes develop significant amounts of condensation during the summer, potentially contributing to indoor air quality problems. do a great job of keeping the humidity down. Natural building materials and an effective ventilation system are the keys to the home's good indoor air quality. In fact it was one of only four test homes in the region that met the EPA's strict indoor air quality standards. At least one visitor to the Smith House felt the benefit of this, noting that his chronic allergy symptoms subsided when he was inside the home.

    Solar heat is only good when it's cold outside
    Although the house passed the test in the heating department, Dr. Feist voiced concern that the large amount of unshaded south glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. might cause overheating in summer. He was right. "The first couple of years, it was tough," Katrin admitted. She constructed a grape trellis, and when the vines finally reached the top of the structure, the home stayed comfortable on even the hottest days. Katrin pointed out that it's reasonably common knowledge that deciduous plants are a great automatic source of seasonal shade, "but when you live with it, and see it, it's totally amazing." She says that with the right shading, there's no need for an active cooling system in Illinois.


    Rob Wotzak is associate editor at GreenBuildingAdvisor.com

    Tags: , , , , , , , ,

    Image Credits:

    1. Katrin Klingenberg
    2. Katrin Klingenberg/e-co-lab
    3. Katrin Klingenberg/e-co lab
    4. Toshi Woudenberg