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PHIUS+ 2018: Getting to Zero


March 1, 2021 - January 31, 2022: PHIUS+ 2018 and Phius 2021 Submission Overlap
January 31, 2022: PHIUS+ 2018 ends

February 1, 2022*: All new project under Phius 2021

*Must have a signed project contract submitted to PHIUS by above date to secure the version.


PHIUS+ 2015 was the first climate specific passive building standard. PHIUS+ 2018 is the first updated revision to the PHIUS+ 2015 standard. The focus of PHIUS+ 2018 is to add more nuance for different building types and support an overall transition to renewable energy. PHIUS + 2018 has three main tiers for certication.

Each tier uses the same method for determining space conditioning targets.

What’s the same:

  • Pass/fail performance-based passive building standard with prescriptive quality assurance requirements
  • Three Pillars: Limits on heating/cooling loads, limits on source energy use, required air-tightness and other prescriptive requirements
  • Climate specificity on a location-by-location basis

New in PHIUS+ 2018

  • Occupant density and building size (envelope to floor area ratio) influence heating and cooling load limits.
  • Calculate space conditioning targets using the PHIUS+ 2018 final calculator below.
  • Read the 2018 update report (email for a copy).

PHIUS+ 2018 Final Calculator v2

The differences between each tier lie in the Source Energy (SE) target and the way renewable energy offsets this SE.


This path emphasizes on-site conservation and efficiency. This path only allows the use of on-site renewables to meet the Net Source Energy target.

Source Energy

What’s the same

  • Source energy used for overall energy budget
  • Source Zero available as add-on certification

Different for PHIUS Core

  • On-site renewable energy offset is calculated based on coincident production and use (utilization fraction)
  • Source Energy limit is applied to the calculated net of the estimated utilization fraction of on-site PV or other renewable electricity generation 
  • Off-site renewable energy generation is not counted.

The PHIUS Core Source energy targets are:

  • Residential: 5,500 kWh/person/yr
  • Non-Residential: 38 kBTU/ft2.yr (120 kWh/ m2 yr)

PHIUS+ 2018

This path moves closer to net zero projects. The limit for source energy is based on a 'fair share' of carbon emissions allowed for each sector.

Source Energy

What’s the same

  • Source energy used for overall energy budget
  • Source Zero available as add-on certification

New in PHIUS+ 2018

  • Source energy criteria tightened, on a path towards zero
  •  No cap on total source energy, but rather on 'Annual net source energy', after offset by qualified renewable energy measures, on-site and off-site. See off-site options noted under PHIUS+ Source Zero below.
  • The airtightness target is now q50 <= 0.06 CFM50/ft2 of gross envelope area

The PHIUS+ 2018 source energy targets are:

  • Residential: 3,840 kWh/person/yr
  • Non-Residential: 34.8 kBTU/ ft2 yr (110 kWh/ m2 yr)

PHIUS+ Source Zero

PHIUS+ Source Zero is a practical and practicable approach to advance community goals of carbon neutrality in the building sector. Source Zero extends from the PHIUS+ Standard, which was developed based on a robust analysis of building optimization to determine a sweet spot for investment in energy conservation measures. PHIUS+ provides numerical energy targets that project teams must meet but retains flexibility and creativity to design to achieve these targets while satisfying other project requirements. Achieving PHIUS+ means dramatically reducing demand. Achieving PHIUS+ Source Zero means meeting the small remainder with on-site or off-site renewable energy.


To meet PHIUS+ Source Zero, the building must generate or procure as much renewable energy as it uses, on an annual, source-energy basis. Because total energy is addressed with a source energy criterion, when it comes to adding an extra badge for “zero”, it was logical to base that on “source net zero”.

On-site renewable electricity generation counts toward source net zero with the same source energy multiplier for electricity, i.e. 2.8. In other words, with the source energy factor for grid electricity at 2.8, every kWh electric generated on site is considered to neutralize 2.8 kWh at the source.

The following arrangements for procuring off-site renewable energy are also regarded as offsetting the source energy use:

Directly-owned off-site renewables.

  • Community renewable energy.
  • Virtual Power Purchase Agreements.
  • Green-E Certified Renewable Energy Certificates (RECs)

For detailed information related to the offset factors for different off-site energy sources & the relationship between fuel switching & PHIUS+ Source Zero, review the Phius Certication Guidebook V3.02.

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