Over the past few years, AUROS Group's most popular blog, by a long shot, has been our original PHI or Phius? What's Right for My Project post from 2020. It's received more clicks than the rest of our blogs combined. Because we work in both Passive House standards and have a pipeline of PHI and Phius projects, we are in a better position than most to compare and contrast our experiences with the two standards. In the original blog, we made the case that it’s prudent to let the project design (new and retrofit) and the owner's performance goals inform the selection of which Passive House standard is appropriate for each project.
As we begin to wrap up 2024, we believe the world of Passive House is scaling rapidly. Building owners and design/construction practitioners are concluding that it's possible to achieve zero carbon without paying a premium in construction costs.
Passive House is not a premium, it’s a learning curve.
Knowing the benefits of a high-performing building envelope, awareness of and interest in aggressive load reduction strategies using Passive House building science are growing rapidly. Certifying Passive House is an important way to reduce financial and performance risks. But, the question remains, “which standard should I recommend to my client?” In this blog, we are clicking a few levels deeper, in a variety of areas, to help you answer that question.
Building Size – Until recently, we would have resoundingly said that very large buildings will naturally lean toward PHI and that much of Phius’ success has been limited to small to mid-size residential – single family and multifamily. That’s not the case anymore. Phius has expanded its portfolio of typologies and sizes of buildings. We haven’t seen large certified mixed-use towers or one million square foot office buildings in the Phius standard yet, but our guess is that it will happen one day soon. It is still fair to say that the PHI community and its list of CPHD/Cs and Certifiers have more experience in large, complex buildings than the Phius community of CPHCs and Verifiers/Raters.
Opinion – Advantage PHI
Climate – Phius appropriately gets credit for having a broader set of weather files for the North American market, but PHI has many certified buildings in climate zones colder than and warmer than climate zones in the United States. The Phius standard includes climate specific certification criteria, while PHI generally maintains the same certification criteria (there is a small climate specific allowance for dehumidification). Be aware that these factors may impact which certification is “easier” to achieve, but may not result in reaching the highest performance possible (i.e. energy, operational carbon, thermal comfort, ventilation rates, etc.).
Opinion – Advantage Phius
Typology – Both PHI and Phius certify all types of buildings. However, Phius appears to be certifying more Accessory Dwelling Units (ADU’s) under 1,000 square feet – where that’s a tall order for PHI’s PHPP to pass criteria. In general, we have found it easier to model non-residential buildings in PHPP compared to WUFI Passive.
Opinion –Advantage Phius
Renewables - Renewables are more of a cherry-on-top of an already amazing project when it comes to Passive House buildings. While we believe producing your own energy onsite or purchasing from community solar PV programs are important, we must remember that Passive House is an envelope-first load reduction approach to building performance. If we optimize the building envelope first and install correctly sized mechanical systems to match, the amount of electricity to run the building is minimized. Both programs allow you to utilize PV to achieve a higher-level certification. Phius ZERO requires an all-electric building with complete renewable offsets utilizing onsite and offsite renewable production. PHI does not require that the entire building energy use is completely offset by onsite or offsite renewables to achieve Passive House Plus or Premium.
Opinion – Advantage PHI
Zero Carbon –While both compliance BEMs (PHPP and WUFI Passive) can calculate carbon emissions, those calculations bear no weight on either certification. The carbon calculations for BEMs are based on blended rate emissions that are typically part of the CPHD/C’s input (Neither BEM program automatically imports hourly and/or annual blended carbon emissions factors.) There is room for innovation in this regard.
Opinion – No Clear Leader
Existing Buildings – Until recently, PHI had a sizable advantage over PHIUS in terms of existing buildings. The EnerPHit standard from PHI provides teams with a certification path along with significant reference buildings to feel confident that virtually any existing building can achieve EnerPHit certification. In 2024, however, Phius introduced their REVIVE 2024 standard which offers a range of solution packages to reach low carbon with an eye on costs.
Opinion –Advantage PHI
Commissioning Requirements – There is some light of day between the two Standards. Phius requires a certified Phius Verifier/Rater to complete field testing, whereas PHI allows anyone to complete this work. PHI requires documentation demonstrating that the testing was completed, and the results were achieved. Also, if IRA funding isn’t pursued, the fact that Phius requires HERS testing can make commissioning more expensive for a large multifamily building. Despite the higher costs for commissioning, Phius’ additional commissioning requirements can increase the team’s confidence in achieving long-term results especially for teams early in their Passive House experience.
Opinion –Advantage Phius
Financing Goals – There are many sources of funds and individual funders that use Passive House certification as an “easy button” path to aggressive energy efficiency. Funders and foundations have realized that the pursuit of a Passive House standard to deliver energy efficiency requirements de-risks building operations and provides a resilient building. Prescriptive approaches to building performance cannot deliver holistic PH solutions that simultaneously drive 1) low energy 2) resiliency 3) healthy indoor air quality and 4) thermal comfort. Passive House standards are uniquely positioned to tackle our generation’s most difficult problems: climate change, fuel poverty and inequitable indoor air quality.
Inflation Reduction Act (IRA) – While the change in Administration will likely affect future allocations of federal funds, it’s important to remember that Section 179D in the IRA has been around since 2005 and has enjoyed broad bipartisan support. Section 45L is focused on housing and, within that category, affordable housing benefits significantly from the ability to combine 45L with Section 42, Low Income Housing Tax Credits. Specifically, 45L credit amounts do not reduce the adjusted basis of buildings pursuing Section 42. As a result, it’s fair to assume that these sections will not be under as much political pressure as other elements of the IRA. We provide this important context to differentiate between PHI and Phius. While either Standard is equally beneficial to achieving maximum value from 179D tax deductions, the Phius standard has a leg up when pursuing 45L tax credits. Section 45L bonus credits must meet US DOE’s Zero Energy Ready Home (ZERH) Multifamily Program. Phius certification requires Energy Star Multifamily New Construction and Indoor AirPlus which are embedded in ZERH. So, in the world of affordable housing, the programs align most cost-effectively with PHIUS.
Commercial Property Assessed Clean Energy (CPACE) – Generally speaking, there is no advantage for one Standard versus the other when considering CPACE financing. CPACE is a financing structure in which building owners borrow money for energy efficiency, or renewable energy and make repayments via an assessment on their property tax bill. PACE Equity’s Cirrus Low Carbon is one program worth mentioning because it has an “easy button” that lowers CPACE financing with Passive House certification and they now accept both PHI and PHIUS certification. Check it out.
Opinion – Advantage Phius
Policy – Both Standards have spent time and money in the United States and Internationally (PHI) to educate policy makers on the benefits of Passive House.
Building Energy Performance Standards (BEPS) – most well known of these are New York’s LL97, Boston’s BERDO, Denver’s Energize Denver, etc. Passive House Network (PHN), on behalf of PHI, is a leader in convening broad swaths of policy makers to understand and incorporate Passive House into their BEPS. Similarly, Phius convenes local and state leaders to enlighten and encourage policy makers to set the proven energy performance goals. Neither Standard has an outright leadership position, so we encourage the leaders of both Standards to represent both Standards equally in policy discussions with jurisdictions of any size. Similarly, leaders of jurisdictions or funders of monies targeted for energy efficiency should never accept the position that one standard has policy advantages over the other. This is not a defensible point of view, and the ecosystem of practitioners needs you to call the ball fairly and equitably, giving us the greatest number of options possible to choose the right tools for every building.
Opinion –There is not enough discernable difference, from a policy perspective, to leave out the opposing Standard. This is a question of choosing code-based criteria or passive house standards. Passive House wins every time.
Tally of AUROS Group Opinions –
PHI = 3
Phius = 4
Bottom line: Jump in the Passive House pool. Quit standing on the edge; just jump.
We hope you’ve found our second installment of “PHI vs PHIUS? What’s Right for My Project -- part 2” thought provoking. You can find more information and white papers at www.aurosgroup.com.
IMPORTANT PASSIVE HOUSE RESOURCE LINKS:
Passive House Accelerator – a global, collaborative platform for sharing innovation and thought leadership in Passive House design and construction
Passive House Reports from Passive House Network -- a collection of reports on public policy, regulations and general information on costs, safety, etc.
Passipedia – Passive House Institute’s (PHI) robust resource library
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