Image Credit: Martin Holladay The Mini-B's compact kitchen has a stainless-steel countertop. The finish flooring in the kitchen is that same as the flooring elsewhere in the house: a 2-inch-thick concrete slab over wood framing.
Image Credit: Martin Holladay Dan Whitmore's Passivhaus duplex has HardiBoard fiber-cement siding and metal roofing. This photo shows the east elevation.
Image Credit: Martin Holladay The west side of Dan Whitmore's duplex faces the street. The larger of the two units is on the west side of the building, while the smaller unit is on the east.
Image Credit: Martin Holladay At Dan Whitmore's duplex, domestic hot water is supplied by a gas-fired Vertex water heater. The black box above the water heater is the Ultimate Air ERV. The smaller box at the upper right contains a copper heat-exchange coil; the coil is in line with the fresh air duct of the ERV system. Space heat is supplied by circulating hot water from the Vertex water heater through this heat-exchange coil. The ERV fans operate continuously.
Image Credit: Martin Holladay Dan Whitmore's duplex uses OSB as the home's air barrier. The OSB was installed on the inside of the wall framing; all OSB seams were sealed with SIGA tape from Switzerland. To avoid penetrating the air barrier with electrical boxes, all wiring is run in a baseboard chase on the interior side of the air barrier.
Image Credit: Martin Holladay This home, the North residence, was designed and built by the Artisans Group. One of the south windows was damaged in shipment, and workers are awaiting a replacement unit from Thermotech Fiberglass. A layer of turquoise housewrap has been installed on top of the vertical rainscreen strapping. The builders used about $2,000 worth of SIGA tape to be sure that the home's envelope has a low level of air leakage.
Image Credit: Martin Holladay Here's a photo of the south side of the North residence -- the same side of the house shown in the previous photo -- taken after construction was complete. The photo was taken in 2013. [Photo credit: theolympian.com]
Image Credit: theolympian.com The North residence has a simple, compact shape. The four glass doors in the home's living room face east.
Image Credit: Martin Holladay At the North residence, provision has been made for air entry into the rainscreen gap between the fiber-cement siding and the fiberboard sheathing.
Image Credit: Martin Holladay The windows at the North residence are neither innies nor outies; they are in-betweenies. Before the windows were installed, the rough sill was protected by a site-built sill pan. The fabrication and installation of the sill took some head-scratching; the final result is a piece of galvanized steel that extends from the window to a drip-edge hanging over the siding. The potential for possible "dribble corner" problems at the extreme edges of the sill remain a concern.
Image Credit: Martin Holladay The water heater at the North residence is a gas-fired instantaneous heater from Navien. The space heating system is similar to the one installed at Dan Whitmore's duplex; all space heat is delivered through the ventilation system. The fresh air duct leaving the ERV is connected to a box containing a hot-water coil; the water that circulates through this coil is heated by the domestic water heater.
Image Credit: Martin Holladay Albert Rooks (left), the owner of Small Planet Workshop, and Mark Dixon, a carpenter with The Artisans Hand, in the unfinished kitchen of the North residence. According to architect Tessa Smith, she chose the stainless-steel range hood that is visible behind Mark for two reasons: it is a recirculating unit that doesn't require an exhaust duct to the outdoors, and “it's sexy.”
Image Credit: Martin Holladay
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 House 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 glazing. 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 mass 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 EPS (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 barrier: liquid-applied WRB
- Domestic hot water: Stiebel Eltron instantaneous electric
- Mechanical ventilation: Ultimate Air RecoupAerator 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-sheathing 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 2×4 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, SHGC=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 Btu/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?”