Phius (Passive House Institute US) certification is a high-performance building certification that aims to achieve extremely low energy use through energy-efficient design, also known as the Passive House concept. Passive strategies such as a thermal-bridge-free enclosure, continuous insulation throughout the building enclosure, and high-performance glazing help the space maximize efficiency and cost-effectiveness, no matter the climate zone or building type.
PHIUS-certified projects typically use 40-60% less energy than buildings built to code. Let’s learn more about what pursuing this certification looks like and how intentional design can have that much of an impact on energy use.
Phius certification is a stringent certification process. The project team must have an understanding of the project site and orientation to determine how site conditions, solar exposure, shading, and building orientation can have a significant impact on the project’s ability to meet Passive House performance requirements. These factors should be considered early in the design process, along with the project’s goals, budget, and overall approach to energy efficiency.
Typically, a certified Passive House consultant + PHIUS rater or verifier (depending on whether it’s a residential or commercial project) will be required as members of the project team. The consultant will help during the design phase of the project, working with the computer model (WUFI / METr) to fine-tune the design and ensure it is on track to comply with the certification goal. The verifier or rater is instrumental during the construction process, conducting on-site visits and ensuring the assemblies are being built according to the drawings to meet certification.
While not a requirement, a contractor familiar with the Passive House process is very helpful. This helps the project remain on track while possessing a better understanding of means and methods needed to achieve certification. An example of this would be constructing high-performance assemblies to pass a blower door test—a test revealing gaps or cracks in the building envelope.
Phius has different certification tracks that projects can pursue. Factors such as the compactness factor, which demonstrates how much exterior surface area the building has relative to its internal volume, determine the PHIUS pathway the project can use.
While the compactness factor of a building is important, heat loss and heat gain can be dependent on the climate zone and location of the building, so it’s important to consider all these factors in the building design. A more complex building may require computer modeling to ensure the building aligns with the Phius performance path.
For example, a compact shape such as a cube compared to a design with “wings” or appendages will have a better surface-to-volume ratio.
Other decisions such as building orientation, openings and arrangement of them—Doors, windows, ventilation, skylights—and building envelope assemblies can impact the energy efficiency of a building.
Assembling a high-performance building envelope is vital for achieving certification. In traditional buildings. For Phius buildings, a common strategy is to wrap thick insulation around the exterior face of the framing like a winter coat to negate thermal bridging.
Products listed as “high-performance” are typically a necessity for Passive House buildings. This is similar to and includes products such as Energy Star products. These options are vetted to reduce energy and water waste while meeting strict standards.
Outside of Energy Star Products and continuous insulation, materials such as triple-paned windows can also have a substantial impact on heat gain or loss. These combined strategies help a building become more efficient and achieve a passive standard.
Of course, meeting the requirements of the certification itself is a challenge. To continue with the blower door test example, this high-stakes audit of the building’s entire enclosure is ultimately a pass/fail test for achieving Phius Certification. A mid-point test during construction can be helpful in discovering and resolving any leaks prior to the wall assembly being fully enclosed and applying finishes.
Another challenge is aligning the assemblies and opening locations with the model to stay on track to achieve certification. This is critical to ensure the building performs as simulated. Otherwise, the project could be at risk of not achieving certification.
Additionally, if project teams are using prefabricated panels for the walls, roof, and floor, the design needs to be “finalized” earlier in the process. This allows enough time for the fabricated panels to be made prior to construction. These panels are an important part of the design because they’re built to meet the strict Phius requirements. Constructing wall assemblies within a temperature-controlled interior environment can be beneficial in lieu of on-site construction.
Overall, achieving Phius certification is a more intensive process, but for good reason: to reduce energy consumption. By understanding things like building massing, orientation, and the cost/time requirements for implementing passive design strategies, project teams can apply these lessons to other projects to achieve higher-performing and more passive designs.
Learn more about deciding if a Phius Certification will fit your project.