Image Credit: Daniel Ernst Once the Zip System sheathing is taped, it acts as a water-resistive barrier (WRB) as well as an air barrier.
Image Credit: Daniel Ernst A layer of OSB-colored nailbase was installed on top of the green Zip sheathing.
Image Credit: Daniel Ernst The ceiling air barrier consists of taped OSB. Strapping was installed under the OSB to create a service chase for wiring.
Image Credit: Daniel Ernst The "innie" windows have careful exterior detailing to direct rainwater away from the vulnerable window opening.
Image Credit: Daniel Ernst Transfer grilles help equalize pressure imbalances between bedrooms with closed doors and adjacent common areas. However, they won't do much to equalize temperature imbalances unless a fan is installed to create a pressure imbalance that forces air movement through the grilles.
Image Credit: Daniel Ernst The energy-recovery ventilator (ERV) hangs from the ceiling of the laundry room.
Image Credit: Daniel Ernst As long as the weather isn't too hot, the ceiling fan in the family room can be used to keep people cool without operating the air conditioner.
Image Credit: Daniel Ernst First floor plan.
Image Credit: Adam Cohen Second floor plan.
Image Credit: Adam Cohen
This custom home, a PHIUS+ certified project, disproves the notion that energy-efficient houses are cost-prohibitive
When the time came for Jason and Stephanie Specht to find a builder, they started out with high ideals. They wanted a builder who wouldn’t skimp on the quality of construction and who wouldn’t charge an exorbitant fee.
Since this was their first time building, there were a lot of unknowns and a lot of questions: As clients, would they be able to customize plans? Select materials and finishes? Could they realize their budgetary goals? Did the builder have a good reputation? Would the house be energy efficient?
Most of all, they were looking for a builder they could trust.
It was a difficult prospect, and their first efforts proved disappointing. After months of learning about the marketplace and figuring out the possibilities, they settled on Structures Design/Build. It was a business that offered custom plans and construction management, one that could take their project from concept to completion.
During their first consultation, Adam Cohen, a principal at Structures Design/Build, asked them if they had considered Passivhaus. (For more information on Adam Cohen, see Passivhaus Practitioners Share Their Success Stories.) Like many people, they had not yet heard of the Passivhaus standard. And, they assumed that energy efficiency was out of their reach — that it was just too expensive.
Reaching cost parity
Adam was quick to present a different point of view. On the contrary, he argued that constructing a Passivhaus wasn’t necessarily any more expensive than constructing a house to meet the existing energy codes. He told them that although their initial capital investment would certainly be larger, their monthly outlay would be the same. In short, Adam believed that by creating an optimized Passivhaus design, they could achieve cost parity with traditional construction.
What is cost parity? Literally, it means equal price. The phrase is often used to evaluate the performance of a new business (i.e. a new manufacturer). Economists say that a business achieves cost parity when they can produce a comparable product at a comparable price. In theory, it doesn’t matter if it is a commodity, a product, or service, the question is whether or not something is truly cost competitive.
In the context of Passivhaus construction, it is the idea that a builder can leverage their knowledge and experience to produce a Passivhaus at a price equal to standard construction, if the energy costs are included in the calculation. It is the idea that the additional capital costs of Passivhaus construction pay for themselves through savings in your monthly utility bill.
Research, research, and more research
Energy-efficient construction that was cost-competitive? What was not to like? Although the Spechts thought it was a great idea, they wanted to learn more about the Passivhaus concept. Jason started researching — and researching. He read the book, Recreating the American Home: The Passive House Approach, by Mary James. He studied the details of other residential Passivhaus projects, and spent countless hours on the Internet. In the process, he learned an entirely new vocabulary.
When the Spechts finally settled with the idea, they met with Structures Design/Build at the building site. And so began the process of designing a Passivhaus. Over the next few months they worked through multiple options: they finalized decisions on foundation type, building size, floor plan, and exterior style. The house would include an attached garage for vehicles, storage space for the canoe and other outdoor equipment, and provide a space where Jason could complete welding projects.
When the building process began, the research didn’t stop; it just took on a different dimension. Since Passivhaus projects often use new materials and techniques, Jason and Stephanie continued with their research and project involvement: they wanted to be sure they made informed decisions along the way.
Securing a loan was easier than expected
Jason worked at a local credit union. And even though he had a solid understanding of residential mortgages, and how to secure a loan at a good rate, he worried that it would be a troublesome process. He attempted to find a bank that offered EEMs (Energy Efficient Mortgages), and prepared to argue the merits of the Passivhaus concept. What he found was disappointing: loan officers were unaware of EEMs, even if their company offered them in their mortgage service portfolio.
In the end, he met a loan officer at a local bank that spoke his language, someone who valued energy efficiency and conservation. And all that worrying was for naught. The building plans were appraised at a value that was equal to the construction contract price — even without figuring in the utility bill savings. This was a pleasant surprise, and confirmed the idea that energy-efficient construction could be cost-competitive.
Now they were ready to break ground and start building.
Build your house on solid foam
Structures Design/Build specified an insulated slab — sometimes called a raft foundation. (For more information on raft foundations, see “Foam Under Footings.”) But unlike most raft foundations, this design incorporated a thickened edge. This had several benefits. One, the only proprietary piece of EPS foam was the integral footer; the majority of the slab could be insulated with standard sheets of EPS foam (readily available in most markets). Two, the slab could be poured at a standard thickness, reducing the amount of concrete required for the foundation.
It was a win-win situation, with lower costs, less shipping, and lower embodied energy.
Rigid air barriers rule
Zip sheathing and tape created the wall air barrier, and standard OSB completed the assembly on the second floor ceiling. The Zip System is gaining traction in the U.S. marketplace and is now commonplace in many locations. It doesn’t take long for a framing crew to install and detail this system to create an excellent air barrier.
Adam wanted to perform blower-door tests at various stages in the construction process. He conducted the first test when the airtight sheathing was first sealed, but before the framing crew cut the window and door openings. This multistage testing protocol helped him quantify and isolate the leakage paths, and later, determine the effectiveness of other air barrier components (i.e. window frames and utility penetrations).
Down come those thermal bridges
The framing crew built a fairly common structure — 2×4 studs, 16 inches on center, with solid lumber headers. They used open-web floor trusses for the second floor (providing a cavity for plumbing and ductwork) and engineered trusses for the roof.
So at first glance, it didn’t look like a Passivhaus structure. However, they later installed 6-inch-thick nailbase insulation over the entire wall, including the gable ends. This brought the nominal R-value up to R-37 and created a wall that was free of thermal bridges.
They later installed a deep layer of cellulose insulation above the second floor ceiling to finish the thermal enclosure.
Small heating and cooling loads
Mechanical ventilation is provided by an energy-recovery ventilator (ERV). The ERV is equipped with a heat-exchange coil on the fresh air inlet; this water-to-air coil is tied into a ground source loop (a plastic pipe buried in a horizontal trench). It is designed to temper the incoming airstream and reduce the temperature difference between exhaust and supply.
A ductless minisplit heat pump covers the peak summer and winter loads; the unit’s indoor head is located high in the stairwell and services both levels.
Transfer grilles help reduce pressure differences between the bedrooms and adjacent common areas, and encourage room-to-room mixing when the doors are shut. (For more information on transfer grilles, see Return-Air Problems.) But according to the homeowners, an open door definitely reduces heat build-up during the hottest summer nights; it also provides the greatest comfort level.
What you don’t see is what you get
Whether the impression is accurate or not, in the U.S. there is a pervasive idea that a green home requires weird architecture, recycled materials, and lots of high-tech gadgetry. Jason and Stephanie often found that it was difficult to explain the Passivhaus concept to friends, family, or site visitors. People touring the house wanted to see all of the innovative features — but in fact, there wasn’t much to show: most of the innovation was hidden behind the siding or the drywall.
Yes, the solar thermal system was visible out front, but the water heater looked entirely ordinary. There was a small black box in the utility room (the ERV) — but that was nothing to get excited about. And visitors could open the windows, admire the depth and heft of the triple-pane windows … but there wasn’t much else to see.
Perhaps it is a cultural artifact, or just human nature, but most people don’t get enthusiastic about air barriers, thick insulation, or low energy bills. The Specht family does. And they are even more excited about the fact that they built a high-quality house—an ultra-low-energy house — without blowing their budget.
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• Get involved! Although they were building a very passive house, the Spechts were very active in the design and build process. This gave them a sense of ownership and control, and contributed to the overall success of the project.
• Material choices had a bigger financial impact than the decision to build to the Passivhaus standard. Fiber-cement siding, hardwood and tile floors, solid surface countertops, and quality fixtures all cost more, period.
• Consider how volunteer organizations can help. A local club, the Roanoke Renewable Energy Electric Vehicle Association (REEVA), installed the solar thermal system — without charge. That’s community activism at its best.
• There is a learning curve with new products and technologies. It took some trial and error to learn how to best operate the minisplit heat pump: during the cooling season they found that letting the unit work longer at low speed provided greater comfort. Also, the Klearwall windows required adjustment by a factory representative. (I should note that these were among the first Klearwall windows shipped to the U.S. market).
• The solar thermal system generates a significant amount of heat inside the laundry room. On a warm and sunny day, the closed loop pump becomes a miniature radiator (i.e. loop temperatures reach 150°F). This is undesirable in the summertime. Placing the water heater in the garage would resolve this issue.
— Daniel Ernst is currently starting a design/build firm, Promethean Homes, in Steele's Tavern, Virginia. He posts regular blogs on his company's web site.
General Specs and Team
|Location:||Climate Zone 4A — Thaxton, VA|
|Additional Notes:||$150/sf includes septic, well, and some site work|
Foundation: Modified “raft” foundation (monolithic slab)
Slab Insulation: Two staggered layers of horizontal EPS foam board (R-18) under entire slab; molded EPS forms at perimeter.
Wall frame: 2x4 studs, 16” on center, with solid lumber headers
Wall sheathing: Zip System sheathing
Wall insulation: R-13 fiberglass batts between studs and 6-in.-thick EPS nailbase insulation (R-37) on exterior of Zip sheathing
Wall air barrier: Zip System sheathing and tape
Siding: James Hardie HardiePanel fiber-cement siding installed over Home Slicker
Exterior trim: MiraTEC composite board trim
Windows: Klearwall windows with triple glazing (R-7)
Roof frame: Truss construction to create an unconditioned ventilated attic
Roof sheathing: 5/8” OSB
Ceiling insulation: Cellulose (R-60) on attic floor
Ceiling air barrier: OSB, sealed with duct mastic and tape
Roofing: Asphalt shingles
HERS Rating: 38
Blower-door test results: 0.6 ach @ 50 Pa
PHPP specific space heat remand: 3.16 kBTU / (ft2•yr)
PHPP estimated site energy use: 5,483 kWh/year (457 kWh/month)
Actual energy use (Mar. - Nov. 2012): 442 kWh/month
Space heating and cooling: Mitsibishi Mr. Slim 9,000 BTU/h ductless minisplit heat pump (MSZFE09NA / MUZFE09NA), supplemented by a coil in the ventilation ductwork that circulates fluid through a buried ground loop
Ventilation: UltimateAir DX200 energy-recovery ventilator
Domestic Hot Water: Solar thermal system with tankless electric-resistance backup
Appliances: Energy Star rated appliances (where applicable), induction range
Lighting: Tube fluorescent and compact fluorescent
• Low-flow plumbing fixtures
• Toto 1.28 gpf toilets
Indoor Air Quality
• Low-VOC paints
• Solid bamboo and ceramic tile flooring
• Balanced ventilation system provides fresh air to living spaces and bedrooms