Phius ZERO Standard Specifications

Below is the Phius 2021 Performance Criteria calculator as well as a summary of program requirements. Refer to the Phius Certification Guidebook for more details.

Key Phius ZERO Requirements

Below is an overview of Phius ZERO requirements. Further detail on each item can be found in Section 3 of the Phius Certification Guidebook.

Passive Conservation

Cost Optimized

Passive conservation strategies, also referred to as passive building principles, reduce heating and cooling demands on an annual and peak basis. They include improved thermal performance of the building enclosure, minimized thermal bridging, high performance windows, optimized solar gain, air-tightness, and balanced ventilation with heat recovery. Phius sets project-specific limits on each of these thresholds based on climate, building size, unit and occupant density. The limits are set per square foot of interior conditioned floor area and project-specific targets can be calculated using the Phius 2021 Target Calculator.


Critical for building durability

Phius sets a pass/fail certification requirement on airtightness. It is per square foot of gross enclosure surface area and has varying limits based on test pressure. Full building pressurization and depressurization tests are required to show compliance with this threshold. For most projects, the threshold is 0.06 CFM50 per square foot of enclosure, but the exact requirements and protocol for each project can be found in the Certification Guidebook.

Active Conservation

In addition to using passive conservation strategies to limit the needs for heating and cooling, the overall building performance must be addressed in the design. This shifts focus to conserving energy in all other energy end-uses for the building such as lighting, appliances, mechanical systems and other equipment. The investment in these strategies is guided by the Source Energy target.

Renewable Energy

Renewable energy is required for Phius ZERO. Renewable energy offsets may come from on-site or off-site generation resources. The amount that can be credited as offset is dependent on the adjust factor for that renewable energy type as shown in the chart. See Certification Guidebook Appendix A for more details.

Appropriate Moisture Design for Assemblies and Details

It is important to avoid risks related to mold and moisture in opaque building assemblies. Phius provides three compliance paths to ensure proper, climate-specific moisture design for all assemblies. Phius also provides interior surface temperature requirements on the interior of windows to minimize risk of condensation. The window condensation risk calculator can be found in the Resource Library. And lastly, the interior surface temperature of thermally bridged construction details must avoid mold growth.

Window Condensation Risk Calculator

Window Comfort

Phius sets a limit on the maximum whole-window U-value that may be used in a building pursuing Phius certification. It is set based on the window height and ASHRAE 99% design temperature for that location. The window comfort criterion applies to all projects, regardless of size. The U-value required scales by window height – the taller the window, the lower the required U-value. The maximum U-value allowed can be calculated using the Window Comfort calculator in the Resources Library.

Use the Window Comfort Calculator

Electric Vehicle Charging Infrastructure

Infrastructure for the current and future charging of electric vehicles (EVs) is required for all residential buildings where parking spaces are required. The number of EV Ready and EV Capable Spaces required depends on the building’s parking requirement. For one-to-two family dwellings and townhouses, 1 EV-Ready space is required per dwelling unit. For multifamily dwellings use the requirements table in the Certification Guidebook.

Combustion & Fireplace Safety

Passive buildings are airtight, requiring special attention to combustion and fireplace safety. For Phius ZERO, fossil-fueled combustion is not permitted. Installed fireplaces and woodstoves must have a combustion air inlet connected to an airtight firebox. Natural draft fireplaces are not permitted in any Phius projects.

3rd Party On-Site Inspection and Quality Assurance

All Phius projects require stringent on-site inspection and testing throughout the construction process. This is conducted by a Phius Certified Rater for single family project or Phius Certified Verifier for a multifamily or non-residential project. Their scope includes, but is not limited to: foundation & pre-drywall inspection, verification of compliance with co-requisite program requirements, whole building airtightness testing, ventilation system balancing and commissioning, room by room pressure balancing, and hot water, heating and cooling distribution system testing. More information can be found in the Certification Guidebook, Appendix E: Rater/Verifier Manual.

Find a Phius Certified Rater or Phius Certified Verifier