Image Credit: Ella Wong (images 1 and 4), Robert Hawthorne (images 2, 3, 5 and 6) The owners of TrekHaus enlisted architect Robert Hawthorne, of PDX Living, LLC, and Bart Bergquist of Willamette Valley Remodeling design and build the to duplex so that it would meet the Passivhaus standard. A soy-based phase-change material called BioPCM was installed behind the drywall of one unit's interior walls and the ceiling on the second floor. The version of BioPCM used in TrekHaus comes in mats 16-in. wide and 8 ft. long that can be trimmed as needed. TrekHaus is equipped with a 4.14 kW roof-mounted photovoltaic system. The floors are cork in one unit, solid strand bamboo in the other.
Updated to reflect the installation plans for the photovoltaic systems.
Work is very nearly completed on TrekHaus, a duplex built to the Passivhaus standard in southeast Portland, Oregon. At some point this spring, if all goes according to schedule, the west unit will be equipped with a 4.14 kW roof-mounted photovoltaic system and monitored for performance for a while before a similar system is added to the east unit. Once the renewable-energy systems are in place, the building is expected to operate at net zero energy with three people in each unit.
While they might not get exactly the same sun exposure, the two homes in this project divide the space under the roof pretty neatly down the middle: the unit floor plans are mirror images, each with 1,556 sq. ft. of conditioned space, three bedrooms and two baths, and a 125-sq.-ft. semi-conditioned workshop.
Passivhaus duplexes are hardly unique – GBA highlighted one in British Columbia in June – but this one does have a few atypical features. The name, for one. The duplex is owned by Ella Wong and Randy Hayslip, who explain in a website devoted to TrekHaus that because Wong is an obsessive “Star Trek” fan, the couple decided to play off the TV series’ “boldly go where no one has gone before” theme and tie it to the notion that the Passivhaus standard in the U.S. ventures into the frontier of energy efficient construction.
Closely tracking performance
Another feature of the building is the soy-based phase-change material, called BioPCM, that has been installed behind the drywall of one unit’s interior walls and second-floor ceiling. The building also is equipped with a system of monitors to track its performance. Students and faculty at the Green Building Research Laboratory, at Portland State University, will monitor the effectiveness of the PCM — the unit without it is the control. They will also study the performance of the shell and the building’s mechanical systems, as well as the effects of occupant behavior on the building’s performance. (One of the PSU grad students suggested testing BioPCM in the building.)
TrekHaus is the second Passivhaus project for a design-and-build team headed by architect Robert Hawthorne, of PDX Living, LLC, and builder Bart Bergquist of Willamette Valley Remodeling, who in 2010 completed a three-bedroom, 1,407-sq.-ft. single-family home in Portland that met the standard. That project, called CoreHaus, attracted the attention of Wong and Hayslip, who liked the idea of nudging a Passivhaus building toward net-zero-energy performance by adding a photovoltaic array.
Mechanical systems in the TrekHaus units include an AirGenerate AirTap heat-pump water heater, a Mitsubishi Mr. Slim SEZ-KD09NA minisplit heat pump, and a Zehnder ComfoAir 350 heat-recovery ventilator. Triple-glazed Thermotech fiberglass-framed windows are used throughout.
Construction costs, excluding the land and PV system but including everything else, came to $150 per sq. ft., noted Hawthorne. Thermal resistance is R-38 for the floor, R-49 for the exterior walls, and R-83 for the roof. Airtightness came in at 0.34 air changes per hour at 50 Pascals pressure difference.
Hayslip, a chiropractor who will use a portion of the first floor as office space, and Wong expect to rent out the second unit sometime early this year.