TrekHaus: How a Portland Duplex Reached Passivhaus Performance on an Urban Infill Lot

In southeast Portland’s Sunnyside neighborhood, a duplex known as TrekHaus demonstrates how the Passivhaus standard can be applied to infill development while pushing toward net zero energy performance. Designed by architect Robert Hawthorne of PDX Living and built by Bart Bergquist of Willamette Valley Remodeling, the project delivers two mirror-image three-bedroom homes on a single urban lot. The name pays homage to the Star Trek franchise, with owner Ella Wong framing the project as an exploration of energy efficient construction on American soil. The approach builds directly on lessons from the Shift House, another notable Passivhaus project in northern Oregon that demonstrated the viability of the standard in the region’s climate.

The Passivhaus Approach to Duplex Design

The two units in TrekHaus share a common roof but divide the interior space down the center, each offering 1,556 square feet of conditioned living area. Every unit contains three bedrooms, two bathrooms, and a 125-square-foot semi-conditioned workshop. The floor plans are mirror images of each other, though the east and west sides receive slightly different sun exposure, a factor that becomes relevant for the photovoltaic systems planned for the roof.

This was not Hawthorne and Bergquist’s first encounter with the Passivhaus standard. In 2010 they completed CoreHaus, a single-family home in Portland that met the rigorous energy requirements and caught the attention of prospective homeowners Wong and Hayslip. That earlier project served as a proof of concept for what could be achieved with careful design and airtight construction in the Pacific Northwest climate. For builders curious about scaling up their own skills, what builders can learn from the world’s tallest Passivhaus building offers valuable insights into how extreme performance targets translate across different project scales.

• Each unit provides 1,556 sq. ft. of conditioned space
• Three bedrooms and two bathrooms per home
• 125 sq. ft. semi-conditioned workshop included
• Mirror-image floor plans maximize construction efficiency
• Sited on an infill lot in Portland’s Sunnyside neighborhood

Phase-Change Materials and University-Led Performance Monitoring

One of the most distinctive features of TrekHaus is the use of soy-based phase-change material behind the drywall. This product, called BioPCM, is installed in one unit’s interior walls and second-floor ceiling. Phase-change materials absorb and release thermal energy as they transition between solid and liquid states, effectively smoothing out temperature swings and reducing the load on mechanical heating and cooling systems. The building science behind these materials continues to evolve, and Birds Wing Passivhaus Duplex represents another project where similar performance-driven material choices were applied to a multi-unit residential design.

The deployment of BioPCM in TrekHaus is not merely a design experiment. Students and faculty at Portland State University’s Green Building Research Laboratory are monitoring the building to compare the unit with phase-change material against the control unit without it. The research extends beyond the PCM to include the overall performance of the building shell, the mechanical systems, and the effects of occupant behavior on energy consumption. One of the PSU graduate students originally suggested testing BioPCM in the building, highlighting how academic partnerships can bring innovative materials into real-world construction projects.

The monitoring program covers several key areas:

• Effectiveness of BioPCM in reducing peak temperature loads
• Thermal envelope performance under real occupancy conditions
• Mechanical system efficiency across seasonal variations
• Impact of occupant behavior on overall energy use
• Comparison between the PCM-equipped unit and the control unit

Mechanical Systems and Thermal Envelope Specifications

The mechanical and enclosure specifications for TrekHaus reflect a holistic approach to energy performance. Each unit is equipped with an AirGenerate AirTap heat-pump water heater, a Mitsubishi Mr. Slim SEZ-KD09NA minisplit heat pump, and a Zehnder ComfoAir 350 heat-recovery ventilator. These components work together to maintain comfort with minimal energy input, while the HRV ensures continuous fresh air delivery without the thermal penalty of open windows. Oregon has seen increasing attention to construction standards and material quality across the industry, and background checks for nail guns under Oregon law illustrate how the state has pursued broader accountability and safety in construction practices, even extending to the tools used on job sites.

The airtightness result of 0.34 air changes per hour at 50 Pascals pressure difference places TrekHaus well within Passivhaus certification thresholds. The triple-glazed Thermotech windows with fiberglass frames combine low thermal conductivity with durability, reducing heat loss at one of the most vulnerable points in any building envelope. The R-83 roof insulation demonstrates the level of thermal protection needed to meet the standard in a climate that experiences cool, wet winters and moderate summers.

Cost Analysis, Photovoltaic Integration, and Net Zero Trajectory

Construction costs for TrekHaus came to $150 per square foot, excluding the land and the photovoltaic systems. Hawthorne noted that this figure covers all other elements of the build, from foundation finishes. For a Passivhaus project in an urban infill setting, that cost represents a competitive benchmark that suggests the standard can be achieved without the extreme premiums often assumed by developers. The economics of multi-unit net zero construction are also explored in how precast concrete duplex construction and net zero energy design work in cold climates, offering a contrasting approach to achieving similar performance targets.

The photovoltaic strategy for TrekHaus involves a phased deployment. The west unit will receive a 4.14 kilowatt roof-mounted system first, and its performance will be monitored before a comparable array is added to the east unit. Once both photovoltaic systems are operational, the building is expected to operate at net zero energy with three occupants in each unit. This staged approach allows the design team to verify system performance and refine the installation before duplicating it on the second unit.

Key financial and energy metrics include:

• Construction cost: $150 per sq. ft. (excluding land and PV)
• West unit PV: 4.14 kW capacity (installed first)
• East unit PV: comparable system (installed after monitoring)
• Target: net zero energy with three occupants per unit
• Combined conditioned area across both units: 3,112 sq. ft.

Infill Development and the Green Building Workforce Pipeline

TrekHaus occupies an infill lot in a established urban neighborhood, a siting strategy that avoids contributing to sprawl while putting energy efficient housing within reach of existing infrastructure and transit. The project demonstrates that Passivhaus design can work on constrained urban parcels, not just on expansive suburban lots. This matters for cities like Portland that are pursuing density and sustainability simultaneously. The connection between green building education and workforce readiness also plays a role, and how Oregon Coast Training Center redefines career and technical education highlights the importance of training programs that equip the next generation of construction professionals with the skills needed for high-performance building projects.

The partnership with Portland State University’s Green Building Research Laboratory adds an educational dimension to the project that extends beyond the construction phase. Real performance data from the monitoring program can inform future designs and help refine the Passivhaus model for the Pacific Northwest climate. The involvement of graduate students in proposing and evaluating innovative materials like BioPCM creates a direct pipeline between academic research and construction practice.

For the broader green building sector, projects like TrekHaus serve as living laboratories. The data generated from the monitoring program has the potential to influence everything from insulation specifications to HVAC sizing guidelines for future Passivhaus projects in similar climates. As the construction industry continues to adopt higher performance standards, the practical experience gained from early adopters becomes increasingly valuable.

Lessons from TrekHaus for the Building Industry

TrekHaus offers several takeaways for architects, builders, and developers considering Passivhaus construction. The $150 per square foot construction cost demonstrates that high performance does not require luxury budgets when the design team has experience with the standard. The use of phase-change materials suggests that envelope innovation can complement mechanical efficiency rather than replace it. The university partnership shows that monitoring and research add value without adding significantly to project costs. The building industry in Oregon has been adopting efficiency improvements across many sectors, and how machine control technology helped Oregon mainline paving cut project time in half is another example of how technology and method improvements are raising productivity and quality benchmarks across the state’s construction landscape.

The phased photovoltaic installation represents a pragmatic approach to achieving net zero energy without requiring the entire renewable energy investment upfront. This model could make Passivhaus-plus projects more accessible to owners who want to spread capital costs across multiple phases. As more projects like TrekHaus come online and share their performance data, the business case for high-performance construction in urban infill settings will only grow stronger.