Catawba College’s Commitment to North Carolina’s First Passive House Residence Hall

By Sophie Martin, Autusa Behroozi, and Justin Shultz

Catawba College’s new 130-bed residence hall is on track to be the first Passive House (Phius) certified residence hall in the state of North Carolina, reinforcing its reputation as one of the nation’s most sustainable campuses. Through advanced energy modeling, research-driven design, and strategic interdisciplinary collaboration, the building is projected to achieve a remarkable energy use intensity of 30 kilo British thermal units per square foot (kBtu/sf) per year, cutting energy use in half compared to a typical residence hall. With Issue for Construction (IFC) documents recently finalized, the project has entered construction and is slated to open in summer 2026.

Off to a Good Start – Aligning Catawba’s Goals to Vision

From the outset, Phius certification was a must-have goal for the new residence hall, guiding every decision. An early collaborative workshop aligned the college and team on three priorities: honoring Collegiate Gothic heritage, enhancing student well-being, and achieving Phius performance standards. Early technical analysis embedded Phius standards into the design, materials, and budget, resulting in a cost-effective, high-performance outcome.

The new residence hall reflects Catawba’s Collegiate Gothic tradition with local brick, stone accents, and pointed arches. A steep, south-facing pitched roof readies the building for future solar, and a south arcade creates a shaded gathering space. Inside, the program balances privacy and community with primarily single bedrooms complemented by generous floor lounges for study and recreation, and gender-neutral bathrooms. Heritage architecture, students’ well-being, and building efficiency are core priorities, reflecting both Catawba’s legacy and its commitment to the future.

Early Decisions – Setting the Groundwork for Significant Impacts

Early decisions set the groundwork for Phius certification and long-term efficiency. During schematic design, the project team shaped the attic strategy, limited thermal bridging, guided mechanical locations, and committed to an all-electric approach. We engaged Build Zero Consulting to leverage their technical Phius expertise, maximizing efficiency on the project.

Optimizing Form and Glazing

Massing and geometry studies informed the building footprint. The orientation and T-shape allow for self-shading. Parametric window studies identified 30 to 40 percent as the best balance of daylight, comfort, and energy use. The 8-inch window depth, coupled with internal shades, is optimal for glare and for thermal comfort.

Thermal Boundary and Attic Strategy

A critical choice was whether to include the 9,000 square feet of unoccupied attic space within the primary thermal and air control layers. The team weighed energy use, air and vapor control complexity, thermal bridging risk, material quantity, embodied carbon, constructability, and cost (see Table 1). The team ultimately excluded the attic from the conditioned envelope to avoid heating and cooling unoccupied space. Mineral wool insulation and the primary air barrier sit at the attic floor, reducing cost and simplifying continuity of control layers. The dedicated outdoor air system (DOAS) was shifted to grade for easier access, fewer roof penetrations, decreased duct lengths, and simpler maintenance.

Mechanical Systems Strategy

The residence hall connects to Catawba’s new geothermal campus loop to take advantage of the earth’s relatively constant underground temperatures for efficient heat exchange. Space conditioning maintains comfort with ground source heat pumps, one of the most efficient HVAC solutions available, paired with a hydronic distribution network that reduces refrigerant volume and associated carbon impacts.

The design uses a fully decoupled approach to ventilation and heating/cooling, allowing each system to operate at peak efficiency. This decoupling prevents over-ventilation to satisfy thermal loads and avoids running heating or cooling solely to meet ventilation requirements. Fresh air is delivered through a DOAS located outdoors that includes a high-performance energy recovery wheel that captures and reuses thermal energy from exhaust air. Early placement studies carefully considered duct lengths to keep energy use low, resulting in a final system layout that reduces losses and maximizes performance.

Plumbing and Electrical Strategies

Domestic hot water uses a geothermal heat pump with a coefficient of performance above 3, roughly triple the efficiency of electric resistance or gas systems. Plumbing design groups bathrooms, custodian closets, and other service cores together to minimize piping lengths, reducing material use and heat loss. On the first floor, a recirculation loop moves water to trunks, branches, and twigs that feed individual fixtures. This layout ensures hot water is delivered quickly by limiting the water volume between the heat source and the point of use.

The building runs on an all-electric, grid-connected infrastructure, allowing it to decarbonize alongside the regional grid, which Catawba College supports by purchasing power from renewable sources. Where possible, appliances are ENERGY STAR certified. These selections meet efficiency co-requisite requirements and further lower operational energy demand.

Data to Decisions – Minor Details, Major Outcomes

Throughout the detailed design process, we maintained consistent and careful coordination across all disciplines through weekly meetings and pull-planning. In parallel, the Page building sciences team ran options to inform data-driven decisions, and Balfour Beatty regularly refined cost and construction models to keep the project aligned with the budget and schedule. Value engineering began early, informed by global material cost challenges. This process aligned vision, scope, and materials with budget and schedule, while meeting Phius performance goals.

Detailed Evaluation of Thermal Bridges

The team reviewed the impact of thermal bridging in WUFI Passive energy modeling software to align design choices with Phius standards. The WUFI Passive model showed that the roughly 400 shelf-angle brackets made a substantial energy impact. The manufacturer’s analysis showed that the stainless-steel brackets performed the best, reducing heat loss and lowering heating demand. Thermal pads offered only minor further improvement, so excluding them cut costs while maintaining strong energy performance.

Page used THERM, a two-dimensional thermal analysis software, to model project-specific conditions such as steel stud penetrations through the attic floor insulation. Each stud rests on a structural thermal break, which reduces, but does not eliminate, thermal bridging. The analysis confirmed that interior surface temperatures will remain above the dew point, avoiding condensation. The point thermal bridging impact, expressed as a psi value, was incorporated into the WUFI Passive model for accurate performance predictions.

Reducing Condensation Risks

Placing the thermal control layer at the attic floor introduced the added challenge of preventing summertime condensation. The metal deck, a vapor-impermeable surface, is exposed to cool, conditioned interior air during summer, creating a potential condensation risk when it comes into contact with warm, humid attic air. In consultation with Build Zero Consulting, Phius, and Rockwool’s building science team, the design addressed this risk with two lines of defense: 1) a smart vapor retarder that will limit downward vapor movement in hot, humid conditions while allowing upward drying in cooler, drier seasons; and 2) a continuous vapor barrier with cover board installed directly above the metal deck.

Iterative Mechanical Ventilation Design

After the enclosure was optimized, ventilation and fans accounted for roughly 16% of total energy use, making them the second largest energy-impact area. The mechanical design followed an iterative process alongside the passive building energy model to reduce ventilation loads while maintaining occupant fresh air requirements. The alternatives considered to achieve these reductions are outlined below.

Design features required for code compliance and occupant comfort included individual room thermostats, minimum fresh air requirements, and interior shading. The project applied additional strategies to reduce ventilation loads, such as limiting the number of custodial closets and improving the efficiency of the energy recovery wheel to offset higher ventilation rates.

The team evaluated several control strategies that were ultimately not implemented. Individual bedroom controls with key-card access were replaced by larger thermal zones served by single heat pumps due to cost and limited effectiveness. For shared spaces, dampers tied to occupancy or CO₂ sensors were considered, but analysis showed minimal energy savings relative to system cost. At a utility rate of 8.2 cents per kilowatt-hour (kWh), the total savings for including dampers in the great room, lobby, study rooms, and other common areas would be $700 per year. However, the cost per damper would be ~$2,500 with the added complexity of maintenance and replacement.

Domestic Water Heating

Domestic hot water accounted for roughly 16% of total energy use, tying ventilation as the second-largest category. Drain water heat recovery was evaluated but not implemented due to high cost and limited energy savings.

Results – Achieving Phius Performance Criteria

Through a rigorous data-driven, and collaborative design process, the project meets performance criteria with a comfortable margin to accommodate construction-phase changes. The energy model will be updated throughout construction to ensure the project remains on track for Phius certification.