Phius CORE Prescriptive Standard Specifications

Below is an outline of the program requirements. Refer to the Phius CORE Prescriptive Checklist linked below for all program details.

CORE Prescriptive Checklist

The Phius CORE Prescriptive Checklist requirements are divided into 10 categories:

  • General Scope & Co-Requisite Programs
  • Air-Tightness
  • Compactness
  • Solar Protection
  • Thermal Enclosure
  • Moisture Risk Limitation
  • Mechanical Ventilation
  • Mechanical Systems
  • Lighting, Appliances & Water Heating
  • Electric Vehicle Ready

Project Eligbility

The Phius CORE Prescriptive program is limited to single family detached residences, townhomes, and duplexes.

For townhomes and duplexes, only vertical partitions are allowed, i.e. only side-by-side projects are allowed. Stacked units are not eligible for this program.

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Phius CORE Prescriptive Checklist

Get into the Phius CORE Prescriptive Checklist. This comprehensive checklist outlines all detailed requirements of the program, and a completed checklist is required for certification submission.
Download the Checklist

Phius CORE Prescriptive Requirements

Below is an overview of Phius CORE Prescriptive requirements. Further detail on each item can be found in the Phius CORE Prescriptive Checklist.

Passive Conservation

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. For the prescriptive program, Phius sets climate-specific requirements on each of these individual strategies with an option for some tradeoffs. Specifics can be found in the Phius CORE Prescriptive Checklist or Snapshot.

View the Phius CORE Prescriptive Snapshot


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 both pre-drywall and at final construction to show compliance with this threshold. The threshold for all projects certifying under the prescriptive program is 0.040 CFM50 per square foot of enclosure.

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. For the prescriptive program, Phius has set individual efficiency targets for each item and also allows the use of a performance tradeoff path.

Renewable Energy

Renewable energy is not required or credited under Phius CORE Prescriptive.

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.

Use the 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 planned. For prescriptive program projects, 1 EV-Ready space is required per dwelling unit.

Combustion & Fireplace Safety

Passive buildings are airtight, requiring special attention to combustion and fireplace safety. For Phius CORE, fossil-fueled combustion is permitted but all heating/water heating systems within the buildings' pressure boundary must be sealed, direct-vent appliances. Installed fireplaces and woodstoves must have a combustion air inlet connected to an airtight firebox. Natural draft fireplaces are not permitted.

3rd Party On-Site Inspection and Quality Assurance

All Phius projects require stringent on-site inspection and testing conducted by a Phius Certified Rater throughout the construction process. Their scope includes, but is not limited to: foundation & pre-drywall inspection, verification of compliance with co-requisite program requirements, whole building airtightness testing (pre-drywall and at final construction), 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