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 LEED 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 EPS 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-value 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 2×6 structural wall, an OSB air barrier, 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 test, 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 heater. 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.