A Contemporary Passivhaus Design in Seattle
A builder's first try at this super-efficient level of construction becomes Home Sweet Home
A Seattle builder and architectural firm have collaborated on a contemporary, three-story home that's won Passivhaus certification, the first in Seattle to do so.
The house, nicknamed "Park Passive," is the work of Cascade Built and NK Architects. It is located in Seattle's Madison Park neighborhood. (The home is mentioned in an August 15, 2013 New York Times article, "The Passive House: Sealed for Freshness.")
Cascade Built founder Sloan Ritchie says he's undertaken a variety of single- and multi-family projects in the past, including some built to LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. standards, but nothing to date that performed at this level of energy efficiency. He and his family moved in this spring.
"We certainly believe in the concept and believe in the energy efficiency and energy savings," he said by phone. "We feel it's very important, so we're interested in doing more of this type of project for sure."
(Dwell Development announced back in March it had built what it thought was Seattle's first spec Passivhaus project. As of July 25, the house had not been certified, although the developer says the paperwork is being processed by the Passive House Institute U.S. Cascade Built's project was certified by an Irish company, Passive House Academy, following the protocols of the Passivhaus Institut, the European counterpart of PHIUS. Two earlier Passivhaus projects in Seattle — Joe Giampietro's Mini-B cottage and Dan Whitmore's duplex, both described in a 2011 blog by GBA senior editor Martin Holladay — have not been certified.)
A contemporary design on an infill lot
NK Architects designed a striking contemporary building that's clad in corrugated metal and capped with a rooftop deck. Completed in April, the 2,710-square-foot house, has four bedrooms and three bathrooms on three levels.
Some of the construction details provided by Ritchie for the slab-on-grade structure:
- There is plenty of sub-slab insulation: 8 inches of high-density 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 under the footings, and another 20 inches of medium-density EPS under the slab itself. The total of 28 inches of foam under the slab has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about 100. (Most of the rigid foam installed under the slab is acting as fill to raise the grade; the foam isn't necessary to meet the home's Passivhaus goals.) The 8-inch layer of foam beneath the footings continues up the outside of the stem walls to connect with exterior wall insulation.
- Exterior walls consist of a 2x6 structural wall, an OSB 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., and 9 1/2-in. deep I-joists with about 15 in. of blown-in fiberglass insulation, for an R-value of about 60.
- Roof insulation, a combination of 24 inches or more of blown-in fiberglass plus 4 inches of polyisocyanurate, has an R-value of about 100.
An initial blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas., before windows or drywall had been installed, came in at 0.4 air changes per hour at a pressure difference of 50 pascals. A later test, after windows went in, was 0.5 ach50.
Whole house ventilation is provided by a Zehnder Comfoair 350 heat recovery ventilator. Domestic hot water is provided by an AirGenerate AirTap 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. . The windows were manufactured by Intus.
When it came to heating and cooling, Ritchie chose a ducted minisplit with a single outdoor compressor and a single indoor fan unit that distributes air via six individual grills. He initially considered a ductless minisplit with a single head, but was stymied by what he thought would be uneven air distribution.
"We thought, OK, we could do one indoor unit, one wall-mounted unit, but where would we put it where it could effectively temper the air in the house?" Ritchie said. "We couldn't really decide where to put it so we realized we just needed to have one where we could get air to multiple locations."
Clean interior details
The house has uncluttered lines and is finished in a variety of materials. On the ground floor, the finished flooring is the concrete slab. On the upper two levels, bamboo is the finish flooring. An ash tree taken from the site during construction was milled into lumber, kiln dried, and used around the house — in the stairwell, for example, and as the vanity countertop in a bathroom.
Outside, the house is finished in a combination of corrugated metal, cedar, and a fiber-cement siding called Silibonit.
Ritchie says he built the house for about $200 a square foot.
- Aaron Leitz Photography
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