Visiting Passivhaus Job Sites in Washington State
The Energy Nerd flies to the West coast, camera and notebook in hand, to document new energy-efficient homes in Seattle and Olympia
On March 16, 2011, I flew to Seattle for a three-day visit to Washington state. Although the main purpose of my visit was to attend the spring conference 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. Northwest, I devoted a day and a half to visiting Passivhaus buildings and construction sites in Seattle and Olympia. With the help of my gracious hosts, Dan Whitmore and Albert Rooks, I was able to see four Passivhaus sites and a large workshop where Passivhaus wall panels were being assembled indoors.
Because I packed in so many site visits and interviews in my short visit to the Northwest, it will take at least two blogs to report on my trip. Here’s the first installment.
Visting the Mini-B Passivhaus
Dan Whitmore is a Seattle builder who kindly volunteered to pick me up at the airport and offer me accommodations for my first night out West. On the way back to his place, we swung by the Phinney Neighborhood Association in Seattle to visit the Mini-B Passive House, a tiny cabin that now sits in a parking lot until the modular building finds a permanent home. The architect of the Mini-B, Joe Giampietro, met us there and gave us a tour.
The Mini-B — short for “mini bungalow” — was designed to meet the “detached accessory dwelling unit” requirements of Seattle's building code. The city allows homeowners to install these small backyard buildings for use as guest rooms or mother-in-law apartments.
Giampietro wanted his Mini-B prototype to meet the Passivhaus standard. As he dove into the design process, he learned first-hand that the Passivhaus standard is much easier to achieve with a large building than a small one. Fortunately, Seattle's climate is relatively mild, and Giampietro was able to achieve his goal — even though the Mini-B measures only 300 square feet.
Since high-performance triple-glazed windows gather more heat than they lose — at least when they face south — the Passivhaus software kept pushing Giampietro's design in the direction of more and more 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.. His final design has an area of south glazing equal to 43% of the home's floor area. The potential for summer overheating is partially addressed by added thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. in the floor; the finish flooring is poured concrete installed over a wood-framed floor system.
Here’s an outline of the Mini-B specs:
- Area: 300 s.f.
- Roof and wall insulation: blown-in fiberglass plus 9 inches of exterior 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. (about R-52)
- Floor insulation: blown-in fiberglass plus 9 inches of exterior EPS (about R-74)
- Windows: U-0.18 windows from Serious Energy
- 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.: liquid-applied WRB
- Domestic hot water: Stiebel Eltron instantaneous electric
- Mechanical ventilation: Ultimate Air RecoupAerator ERVEnergy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
- Air leakage rate: 0.40 ach50
To learn more about this house and others mentioned in this blog, be sure to click on the photos and read the captions.
Dan Whitmore’s Passivhaus
Dan Whitmore, the founder of Black Bird Construction, owns two adjacent residential lots in an attractive South Seattle neighborhood. He and his family live in the older building on the upper lot; on the lower lot, Dan is completing a duplex that, if all goes as planned, will be the first certified Passivhaus building in Washington.
One of the two units in Dan’s new Passivhaus is nearly complete, and I was honored to be offered accommodation there. According to Dan, I was the first person to spend the night in the new home.
Like The Artisans Group in Olympia, Dan follows Katrin Klingenberg's wall-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. recommendations: namely, use interior OSB as the air barrier and vapor retarder, and use vapor-permeable fiberboard as the exterior sheathing.
- Area of two units: 2,589 s.f. (“treated floor area” = 1,895 s.f.)
- Slab insulation: varies from R-20 to R-50
- Wall framing: 14-in.-thick Larsen trusses (with 14-in.-thick double 2x4 walls where needed for structural reasons)
- Wall insulation: 14 in. blown-in fiberglass (R-55)
- Roof insulation: 18.5 in. blown-in fiberglass (R-68)
- Air barrier: interior OSB sealed with SIGA tape
- Windows: triple-glazed units from Cascadia (U-0.18 and U-20, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.=0.57)
- Domestic hot water: A.O. Smith Vertex gas water heater
- Mechanical ventilation: Ultimate Air RecoupAerator ERV
- Space heat: A hydro-air system using hot water from the domestic water heater circulating through a copper coil in the ventilation system’s fresh air duct; backup provided by wall-mounted electric resistance heaters.
- Air leakage rate: 0.41 ach50
I would describe Dan's space heating system as experimental. Unless he wants to overventilate, he'll need to keep the air flow rate of his ERV system at no more than 60 cfm of outdoor air. Since he has no plans to mix recirculated air into the air stream of his combination ventilation / space heating system, the system won't be able to deliver much heat. The heating coil from Ultimate Air is rated at 8,700 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 — but that rating is predicated on a high air flow rate of 200 cfm and a high water temperature of 160°F. The air flow through Dan's system will be only about 30% of the air flow used to rate the heating coil. At lower water temperatures and lower air flow rates, the heat output of the coil drops.
For more information on the Ultimate Air heating coil, see Heating Options for a Small Home.
The North residence
On March 17, Dan gave me (and three architects on their way to the same conference) a ride to Olympia, where we were met by Albert Rooks. Albert’s business, Small Planet Workshop, imports and distributes European building materials, including SIGA tapes. (For more information on SIGA tapes, see One Air Barrier or Two?)
With Albert as my tour guide, we headed to the North residence, a Passivhaus project spearheaded by a local design/build firm, The Artisans Group. The single-family home was still under construction.
The Artisans Group is headed by co-owners Randy Foster and Tessa Smith; Smith is also is the firm’s designer. The North residence is one of three Passivhaus projects that The Artisans Group currently has under construction.
Here are some specs for the North residence:
- Area: 2,350 square feet (“treated floor area” = 1,900 s.f.)
- Foundation: an “insulated raft” foundation (monolithic slab over foam)
- Slab insulation: A continuous horizontal layer of R-75 EPS
- Wall insulation: blown-in fiberglass (R-57)
- Roof insulation: blown-in fiberglass (R-80)
- Wall framing: Larsen trusses
- Exterior sheathing: fiberboard
- Windows: Triple-glazed Thermotech Fiberglass 322; SHGC=0.60 (glazing only)
- Finish flooring: concrete on first floor, polyurethaned plywood on second floor
- Domestic hot water: Navien natural gas instantaneous heater
- Mechanical ventilation: Ultimate Air RecoupAerator ERV
- Space heat: A hydro-air system using hot water from the domestic water heater circulating through a copper coil in the ventilation system’s fresh air duct.
- Air leakage rate: 0.38 ach50
According to Mark Dixon, one of the builders on site when we visited, the fiberboard wall sheathing was unable to resist the pressure of the dense-packed blown-in fiberglass insulation. After the insulation contractor finished insulating the walls, the fiberboard had bellied out and was bulging as much as 3/4 inch in some stud bays. The workers eventually managed to force the bellies back, at least partially, but the experience revealed one potential drawback of fiberboard sheathing.
More to come
Later that day, Albert and I visited another project of The Artisans Group, the Freas house. We also stopped by a wall-assembly workshop at the Satsop Business Park where The Artisans Group is building 17-inch-thick wall panels for an upcoming Passivhaus project; the workshop is located in an abandoned nuclear power plant.
To learn more details about the Freas house and the Satsop nuclear power plant — as well as the proceedings of the Passive House Northwest conference — you’ll have to wait for my next blog.
Last week’s blog: “Are Passivhaus Requirements Logical or Arbitrary?”
- Martin Holladay
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