PHIUS vs PHI – Lessons learned webinar recap

Katrin Klingenberg, PHIUS Executive Director


Thanks to all of you who took the time to join us for last week’s webinar on the differences between the PHIUS and PHI passive house and building standards. Due to popular demand (we sold out within 3 hours of the original offering) we had to get a bigger “boat” and were eventually able to get everyone seated!

Clearly, there is a lot of interest in the topic.

Two passive building design/construction standards are available in the North American market: The PHIUS+2015 Passive building Standard certified through the Passive House Institute US and the Passivhaus Standard certified through the German Passivhaus Institute.

We presented the webinar in response to growing confusion about the differences between standards and questions about how the programs compare to commonly used energy standards such as ASHRAE 90.1. Other common questions: Are they simply “two flavors of the same thing” or are there more fundamental differences between programs? Which program is more commonly used in North America’s widely varying climates and why?

As we all make progress in mainstreaming passive building to significantly reduce carbon globally, one lesson has become clear: details matter! Different standards and modeling protocols offer significantly different guidance to designers seeking cost- optimized, high-performance buildings in their region.

The European standard and its design parameters for energy comprise one target for heating and cooling to attain an optimized design solution in all climates and cost structures worldwide. The PHIUS+ tailors and optimizes energy targets for both climate and cost, and does so for every individual location. The updated 2018 version becomes even more granular by taking occupancy and building typology into account.

Two very different approaches.

If you missed the live webinar, you can still learn more about the differences and modeling protocols: A recording of the webinar is now online!

Some of the questions that were asked during the webinar and could not be answered are posted below and if you have any other questions please send us an e-mail at

Thanks again to all of you who attended!


A selection of Questions posed during the webinar event, that could not be addressed live due to time constraints:

When will PHIUS+2018 come into effect? How long can we continue to use 2015 for projects in development?

PHIUS+2018 will be launched at the Annual conference this September in Boston. Teams can still use PHIUS+2015 until March of 2019.

What can we carry forward as a message from PHIUS & you to building code legislators?

We have put a lot of thought into making PHIUS+ a good standard for how much the building sector contributes to climate goals and/or the renewable energy transition, while also protecting occupant health and comfort. We have given it features to make it suitable for policymakers to incentivize. We can do feasibility studies for specific model buildings in specific climates to give officials a better feel for what PHIUS+ requires and delivers.

It is my experience that PHIUS at this time does not accept published efficiencies of ERV’s, and therefore the derated efficiency of ERV’s are not compatible with PHIUS certification requirements.

We accept 3rd-party ratings from AHRI, HVI, and PHI as well as our own product program – only unverified manufacturer data is derated. For building project certification there is not a hard requirement on recovery efficiency for the ventilation, but yes, in some climates it will be hard to meet the other performance criteria without a good H/ERV.

Can you expand on the adaptation aspects of passive house for the changes which are observed and expected in climate?

Right now, our certification is based on TMY3 climate data, and will update when newer data becomes available. Although predictive future TMY climate data sets exist, these are not used for certification. Even so, the performance upgrades required to meet our criteria should provide resilience benefit against weather extremes and utility outages. Resilience and adaptation to changing climate can be evaluated in a different way, more focused than modeling a typical year for predicted energy performance. We are working on a form of resilience assessment for that purpose.

Followup comment by another attendee: I took the climate question to mean: if standard is zone-variable, can we on top of that adapt to how existing zones are shifting to becoming one zone warmer. 

We are working on calculations that would generate climate data taking possible changes into account.

Wasn’t PHI’s cost-optimization based on integrating ventilation into the heating ducts and not cost of PV?

The idea was to improve/invest in the envelope to a point so that a typical heating system, and the cost associated with it, could be eliminated. The now minimized heating system could be integrated in the ventilation supply air stream using the same fan and ductwork for delivery. In Germany, eliminating the heating system supposedly made up for the additional cost to improve the envelope. In the U.S., because ducts and furnaces are relatively cheap, that strategy does not net much if any savings after one adds the HRV. PHI did not include cost of PV at the time because it was cost prohibitive. In the U.S. today PV is no longer cost prohibitive and at some point becomes competitive with insulation. Yes, the point was that in the U.S., because ducts and furnaces are relatively cheap, said integration doesn’t net much if any savings after you add the HRV.

Has E-Quest been calibrated against measured building performance for a large sample size of buildings?

I would assume so, it is widely used for code compliance modeling.

Is there a bigger sample size of monitored data on single family homes like the one in Oregon?


Is there any measured data to correlate with the modeling comparisons on Slide 27?

The NYSERDA study was on model buildings not actual, so we can’t get a direct comparison in that case.

In the future will there be more resolution than the ASHRAE climate zones for space conditioning criteria?

In all likelihood yes.

Going back to the financial graph, would you say that solar thermal is pretty incompatible with PHIUS or could it still be useful in certain climate areas?

At this point it appears not to be very cost-effective, but it could still have a resilience benefit in some climates. System complexity works against resilience, and climates that require freeze-protection tend to have more complicated systems.

Why PHIUS? To Be Part of the Solution

Some inspirations from the Seattle conference to kick off 2018

At PHIUS, we’ve been at this passive building business for a good long while. And we’ve been inspired to see so, so many professionals join and build our community. Every year we’re all so busy that it’s pretty hard to find the time to just talk about why we’re all doing what we do. That’s why each conference is such a blast.

To capture a little of that fun–and inspiration–we asked a question of some attendees at the 2017 North American Passive House Conference in Seattle, Washington. The question:

Why do you build to PHIUS standards?

Here are some answers and comments we received–we hope you can relate to one or more of them, and please feel free to chip in your own answers in the comments section.

Elizabeth Correa, LMN Architects, Seattle: I design to PHIUS standards because it was a standard that allowed me to align my principles, my design principles, and ethical principles.


Sam Rodell, Rodell.Design, Spokane, Washinton: Building to the PHIUS standard is, I would say, our practice considers that to be our baseline and I think that anyone who builds today and does not consider the possibilities of what is happening here with building science wanders around in a dangerous territory of what I would consider to be professional negligence.


Lindsay Schack, Love | Schack Architecture, Bozeman, Montana/ Driggs, Idaho: I found PHIUS when I was researching affordable and high-performance wall assemblies for a client of mine. And once I found out about PHIUS, I went down this rabbit hole of learning building science, and now I can’t go back. I can’t, with good conscience, build to code anymore. I have to push farther.


Doug Farr, Farr Associates, Chicago, Illinois: Our practice is devoted to sustainability. We’re architects and we are striving to achieve PHIUS+ on a couple of projects, one is a new build and one is a rehabilitation. It’s challenging and frankly, that’s why I like it.

Schack: PHIUS, the institute, not only provides you with support and knowledge, it provides you with camaraderie, and I’ve learned from great professionals, and it has pushed my projects to a level that is gaining notice in my industry and where I live.

Correa: And that marriage between building science and architecture through PHIUS has made me passionate about architecture again and passionate about our mission to address the problems of climate change.

Farr: Some of the other systems which are also worthy and ambitious also are hard to do, but they all have what Kat always calls a ‘get out of jail free card,’ which is that you can always compensate for building a less efficient building by adding more PV or renewable energy.

Correa: And I realize that buildings being a large percentage of the carbon emissions problem and I don’t wanna be part of the problem. That is why PHIUS is especially important to me.

Farr: Passive House is the gold standard.

Correa: I’m part of the solution and I’m not any longer part of the problem.

PHIUS+: The path to positive energy

Become a PHIUS+ Professional and be a leader in the industry


Message from the Executive Director

Katrin Klingenberg, PHIUS Executive Director

Katrin Klingenberg, PHIUS Executive Director

Congratulations PHIUS professionals: thanks to your hard work, 2017 was perhaps the community’s best year ever! Together, in what was in other realms a tumultuous year, we maintained our focus and commitment to make high-performance passive building the mainstream market standard and best practice on the path to zero energy.

By the end of 2017, more than 1500 families now enjoy the benefits of buildings that are safe and comfortable for people and the planet. The buildings are thermally comfy, provide constant healthy indoor air, maintain safe living conditions during outages, produce super low cost utility bills, and are built at affordable costs. And they produce either zero CO2 or tiny amounts our planet can handle.

That is leadership in the most excellent way, urgently needed progress and really, really good news!

2017 highlights at a glance –

  • By all measures, PHIUS+2015 is the most successful passive building system in North America in 2017!
  • Under a previous grant and longstanding efforts, PHIUS jump-started the multifamily trend that continues to go strong. To maintain that growth, PHIUS received a grant from the Illinois Clean Energy Community Foundation to facilitate commercial certification protocols and uptake.
  • The 12th Annual North American Passive House Conference in Seattle was a huge success—a point of particular promise was that international sessions and keynotes showed global interest and relevance of PHIUS+2015 in other global regions.

    Signing cooperation agreement between PHIUS & PHIJP

    Signing cooperation agreement between PHIUS & PHIJP

  • PHIUS+ will soon be available in Japan—details of the collaboration with the Passive House Institute Japan (PHIJP) will soon be announced.
  • Research highlights:
    • PHIUS+2018, the scheduled update and evolution of PHIUS’ climate specific standard, is nearly ready for release for public comment. (Learn more at the Intro to PHIUS+2018 webinar on February 15)
    • Monitored data for the first PHIUS+ certified and quality assured multifamily projects match modeled performance predictions by +- 7%–proving we’re on the right track with PHIUS+ processes and tools.
    • PHIUS and Rocky Mountain Institute partnered to work under a DOE grant for retrofit research.
    • The Industry Advisory Council progresses with proof of concept of and all- climate monitoring project, funding installations in multiple zones.

In 2016, the Canadian Pembina Institute predicted exponential growth in the passive building sector. Their graphs showed that PHIUS certified the vast majority of all passive projects in North America up to that point and was generally on a trend to more than double certifications each year, as PHI certifications were declining.

In 2017 PHIUS met and slightly exceeded projected certifications for the year: Certifications more than doubled compared to 2016. PHIUS certified all but 1 passive building project in all of North America in 2017! And this year 100% of all certified projects had PHIUS trained professionals on the team. CPHC®s, PHIUS® Builders and PHIUS® RESNET Raters/Verifiers will continue to anchors of nearly all teams certifying projects.

This is a great endorsement of PHIUS+2015 certification: Climate specific design methodology assures appropriate thermal comfort, cost optimization assures avoiding pitfalls like over-investment in the envelope, and industry-standard quality assurance protocols endorsed by our partner the DOE eliminates risk of building failure. PHIUS+2015 has proven itself as the industry’ leading passive building system.

Beach Green Dunes in Queens, New York

Beach Green Dunes in Queens, New York

In 2016 we were thrilled to celebrate the milestone of reaching over 1 million square feet of PHIUS+ certified and pre-certified projects across 900 units – and families – nationwide. It took five years to reach that milestone. In 2017 alone we nearly doubled that square footage, reaching 1.75 million square feet of PHIUS+ certified and pre-certified projects across 1,500 units. Wow!

2017 has continued to be a great year for multifamily passive building projects, led by uptake seen in the affordable sector. We are very proud of the great strides the community has made in bringing the benefits of passive buildings to more people than ever before—and to the people who need it most.

In 2017, a marquee multifamily project—Steve Bluestone’s Beach Green Dunes in Queens, New York, became the first mid-rise project in the country to be completed. Its 101 units are now occupied and the project started winning awards right out the gate. It is not only passive, but also uses onsite PV and CHP to generate one third of projected energy consumption. It’s a model project illustrating the path to zero energy and emissions. New projects in the pipeline are getting even bigger: 425 Grand Concourse, a 28 story affordable hi-rise has completed planning and is scheduled to break ground in 2018. Many housing agencies across the country continue to support affordable multifamily developments.

The really good news: The Pennsylvania Housing Finance Authority (PHFA) was the first affordable housing agency to recognize and reward passive buildings. A study of projects spurred by the PHFA, as well as other affordable MF projects around the country, shows costs coming in at 0-2% additional costs over conventional projects. The cost-optimized targets are working!

RMI Innovation Center Basalt, CO -- PHIUS+2015 Certified, PHIUS Source Zero Energy Certified

RMI Innovation Center Basalt, CO — PHIUS+2015 Certified, PHIUS Source Zero Energy Certified

Commercial developments are also being submitted for PHIUS certification. The RMI Innovation center was completed in 2016, winning Best Overall Project in the Annual Passive Design Competition for that year. RMI’s leadership spurred other commercial project teams to conduct feasibility studies, and several are in various states of completion: A planned office hi-rise in Chicago, an administrative building in Spokane, Washington, with a commercial kitchen, a church in Hudson Valley, New York, and multiple school buildings are underway, aiming for passive even for zero energy. (Learn more about the RMI Innovation Center at the Commercial Webinar Series kick-off presentation on February 7)

Following the multifamily approach, we look to lead a similar spike in adoption in the commercial sector. Thanks to a generous grant from the Illinois Clean Energy Community Foundation in 2017, we are in the process of assembling an online Commercial Resource Center; a companion to the MacArthur Foundation funded Multifamily Resource Center that we launched in 2016.

The Commercial Resource Center will serve as an information hub for developers, policymakers, and investors in the design, financing, and execution of commercial passive buildings. We have demonstrated with projects such as the RMI Innovation Center in 2016 that the PHIUS+ Passive Building Standard can be more cost-effective than business-as-usual commercial construction practices to reach zero and positive energy targets. The Commercial Resource Center will help to make even more of these projects a reality.

The encouraging growth in the commercial and multifamily sectors was fully illustrated during sessions at the 12th Annual North American Passive House Conference in Seattle. The conference sold out for a third year in a row and sparked an advanced level of discourse, especially in the building science field.During our 3rd Annual Design Awards Ceremony the Best Overall Project prize was awarded to Elm Place, an affordable multifamily housing development in Burlington, Vermont. A successfully certified PHIUS+2015 project, it elegantly proved the cost effectiveness of the design targets: The project was realized at a 2% cost premium in climate zone 6! Congratulations to CPHC Chris West and his team for this outstanding project! (Learn more about Elm Place at the Developers Webinar Series presentation on January 30)

Milton, VT -- PHIUS+ 2015 Certified

Elm Place, Milton, VT — PHIUS+ 2015 Certified

Internationally, building scientists and government organizations have taken notice of the PHIUS’ unique, climate specific approach, and approached PHIUS about potential collaboration. In August of 2017, Mike Kernagis and I went to Tokyo to keynote the kick-off symposium of the Passive House Institute of Japan (PHIJP). There we signed an international collaboration agreement between PHIUS and PHIJP. In 2018 we will work together to generate cost optimized design targets for the climates of Japan and to translate training materials and certification protocols. Following our keynotes in Shanghai, China, in November of 2017 we were invited to send a keynote presentation on our work in the US to be presented to the attendees of the 4th Chinese Passive Building Summit. More international collaboration talks are to follow in 2018.

In conclusion, a few more notes on research: PHIUS is committed to excellence and continued improvement of the design methodology and standards. We recalibrate the standards regularly to make sure that they are optimized to changing market and climate conditions, as well as advances in components. PHIUS+2018 will be released soon for public comment and adoption. (Learn more at the Intro to PHIUS+2018 webinar on February 15)

Our goal is to have the effort continuously informed by hard monitoring data from certified projects. That effort has been launched by the Industry Advisory Council, a group of leading passive building component manufacturers. In 2017, thanks to the IAC, we selected 6 pilot projects, representing key typologies and climate zones. We finalized appropriate monitoring protocols and selected equipment manufacturers and installation is underway at the first projects. The pieces are now all in place and we will use our pilot project experience to streamline and replicate the monitoring processes, with end goal of making it a fairly routine option available during the PHIUS+ certification process.

Under a DOE grant, PHIUS and RMI will work to provide guidelines and practices for exterior scalable retrofits of projects to achieve zero energy buildings. Work on this project will kick off in January in Boulder, Colorado.

This is all thanks to all of the partners, certified professionals, manufacturers and other supporters who help us advance passive building each and every day. We have accomplished so much already, but there is still much great work left to do. Looking forward to what I believe will the best year ever!

Katrin Klingenberg
Executive Director, Passive House Institute US | PHIUS

Why PHIUS? Because Climate Specific Design = Quality Assurance

Why do you build to PHIUS Standards?

Asked at the 2017 North American Passive House Conference in Seattle, WA.

Lindsey Elton, ECO Achievers:  …E-L-T-O-N like Elton John…

I believe in PHIUS because the organization has taken an extremely detailed look according to our climate zone of what it takes to build a net-zero home or a net-zero building.

Peter Marciano, Legacy Buildings, New York, NY: I’ve come to the conclusion based on what I’ve built that there’s a lot of information out here. There are several passive house programs available. And, for me, having come to the realization that it has to be climate-specific because that’s what works. That’s what works in this nation. That’s what works in this country.

Marc Rosenbaum, EnergySmiths, West Tisbury, MA: I’ve been doing this for almost 40 years, and one of the things that PHIUS brings to the table here that are so amazing to me is people are interested in the actual performance of the buildings. They’re measuring them. They’re comparing them to what they thought they should do, and it’s a really terrific community that is sharing the information to make better buildings.

Elton: They’ve taken all the guesswork out, they’re doing the calculations, and they were smart about it. And we can employ this time after time after time again.

Marciano: If it’s not climate specific, I have had definite problems with certain aspects of my enclosure and certain aspects of my building. And I wouldn’t make that mistake again. I would definitely use a climate specific standard to establish… To build my next passive house.

Rosenbaum: And I think we all know why we’re doing it. We’re doing it because we care about the climate, we care about the kids, we care about other species besides ourselves. And we don’t talk about that. We talk about BTUs, and thermal bridges, and solar heat gain coefficients.

Elton: We’re firmly behind it, our company’s firmly behind it. We believe in it, and that’s why we’re here.

Rosenbaum: PHIUS has really created this community of people, who I think, care about each other’s learning, and share our successes and our failures, and it makes all of us better.

PHIUS+: The path to positive energy

Become a PHIUS+ Professional and be a leader in the industry

Comparing ASHRAE 90.1 Appendix G / PHIUS+ / Passivhaus methods and standards

– James Ortega, PHIUS Certification Staff

The New York State Energy Research and Development Authority (NYSERDA) promotes energy efficiency and the use of renewable energy resources. NYSERDA has been at the forefront of promoting adoption of passive building in NY State. For example, over the past several years, NYSERDA has partnered with PHIUS and other organizations to offer qualified students substantial fee reductions for passive house professional training.

For the past year, PHIUS has collaborated with NYSERDA on a vital study of multifamily buildings in New York. The results of that study were released this past October, and we’re excited to share some of the summarized highlights that show we are on the right track with PHIUS+.

NYSERDA conducted the study to compare standards and methodologies to inform its development of the Multifamily New Construction Program (MF NCP). This program follows the goal of 40% reduction in greenhouse gas emissions that New York State set as part of the Clean Energy Fund (CEF), one of the pillars of the Reforming the Energy Vision (REV) program launched in 2014.

The study is part of NYSERDA’s exploration of alternative approaches and standards to promote high-performance buildings to supplement the ENERGY STAR® Multifamily High-Rise (MFHR) program, which NYSERDA has supported in the past.

The goal of the study is to create equivalent building performance targets for each certification program with the intent that the submitted projects achieve similar energy performance to qualify for incentives offered through NYSERDA’s new MF NCP, regardless of which energy modeling tool and protocol are followed.

Comparing ASHRAE 90.1 Appendix G_PHIUS+_Passivhaus methods and standardsStudy Description

This case study emulated a typical high-rise multifamily building designed and constructed in New York State based on the DOE/PNNL Prototype Models. The five design cases created and modeled using the three tools and protocols described above are listed below[i]. You can also review a fully detailed description and full PDF version of the NYSERDA report here.

Energy Modeling Tools

The study looks at and compares three different approaches and energy modeling tools and protocols.

  • The MFHR program uses the Quick Energy Simulation Tool (eQuest) in combination with ASHARE 90.1 Appendix G Performance Rating Method as the modeling tool and protocol
  • WUFI® Passive is used by the Passive House Institute US (PHIUS) to model performance
  • The Passive House Planning Package (PHPP) is used by the Passivhaus Institute (PHI)

Note: There neither was nor is an expectation that the three different methods would yield equal energy usage estimates because each protocol has different assumptions for operating conditions.


The Base Case and Packages A-C have prescriptive envelope and mechanical systems, but some assumptions such as occupancy, residential plug loads and residential lighting patterns vary based on the different modeling protocols from each organization. As shown in Figure 1 below, the difference in results between protocols is substantial.

For example, the PHI protocol estimate for source energy usage is nearly half of the Appendix G cases. This discrepancy stems directly from the PHI assumptions for residential plug loads and lighting.

Figure 1: Annual Source Energy by end use and Protocol (Using EPA Portfolio Manager Site-to-Source Conversions)

Figure 1: Annual Source Energy by end use and Protocol (Using EPA Portfolio Manager Site-to-Source Conversions)

The NYSERDA report explicitly calls out the plug loads category. First, while acknowledging that some difference in plug load assumptions were to be expected, the report finds the size of the difference troublesome, suggesting that the PHI assumptions are overly optimistic and warrant review.

From the report:

            Variations in this category [plug loads] are expected due to differences in the protocols’ assumptions, but the magnitude of the difference appears excessive, and warrants further investigation. Aside from affecting the total electricity consumption, plug loads interact with heating and cooling and significantly impact the total energy use of high-performance buildings.

The report summarizes that:

            PHI defaults for in-unit lighting and appliances energy use are significantly more optimistic than presented in references such as Building America and COMNET, which contributes to a much lower EUI projected by the protocol for equivalent design. It is recommended that PHI review those default assumptions made regarding multifamily buildings in the U.S.

Packages D-F designs include changes to envelope and mechanical systems by PHIUS and PHI to comply with their respective standards. The proposed design changes by PHIUS and the PHI for these cases are translated into eQuest to investigate the associated energy savings/difference that eQuest registers. There are some exclusions to these proposed changes that are left out of the eQuest model. For example: Both the PHIUS and PHI models incorporate interior blinds to incorporate passive cooling, but Appendix G protocol does not allow manual controls to contribute towards savings.

The difference in Source Energy by End Use between PHIUS and PHI improvements as modeled in eQuest are minimal as shown in Figure 2 below. However, the difference in envelope assumptions are not (particularly windows and airtightness) as shown in Figure 3.

The PHIUS Package (D) uses windows with overall U-value of ~0.28 Btu/hr.sf.F and an airtightness limit following the PHIUS protocol of 0.05 cfm/sf @50Pa. The equivalent infiltration at natural wind pressure is 0.017 ACH. The PHI Package (F) uses windows with overall U-value of 0.15 Btu/hr.sf.F and an airtightness limit following the PHI protocol of 0.6 ACH @50Pa. The equivalent infiltration at wind pressure is 0.05 ACH. The difference in required window U-value between these two models has significant cost implications in that the PHIUS modeled window performance could be met with high performing double-pane windows, while the PHI modeled window performance could only be met with triple-pane windows.

When it comes to airtightness, Appendix G protocol assumes an infiltration at natural wind pressure of 0.186 ACH. PHIUS protocol mandates an airtightness 10x tighter than the Appendix G Baseline for this building (0.017ACH). The airtightness is specified for this particular building because the PHIUS limit is per square foot of envelope area, which equates to varying ACH values with different building sizes. While the PHI target of 0.6ACH @50Pa may be comparable to the 0.05cfm/sf @50Pa target of PHIUS for small buildings, for large scale buildings such as used in this study, the PHIUS target is 3x tighter than the PHI requirement. (0.017ACH PHIUS vs 0.05ACH PHI). This difference in requirements has important ramifications for building durability as well as energy loss.

Figure 2: Energy by Protocol and End Use (Using EPA Portfolio Manager Site-to-Source Conversions)

Figure 2: Energy by Protocol and End Use (Using EPA Portfolio Manager Site-to-Source Conversions)

Figure 3: Modeled Configurations - Packages D-F window U-values and airtightness

Figure 3: Modeled Configurations – Packages D-F window U-values and airtightness

This comparison study is an important step for financing bodies and agencies to meaningfully evaluate performance and incentivize passive buildings. It also serves as a solid case study to build upon for other building types and sizes across the country. As larger passive projects continue to develop, monitored data will become an important assessment tool to verify the modeled results of comparison studies such as this one.


[i] Base Case: ASHRAE 90.1-2010 Appendix G Baseline Design

Package A: Base Case modified to include building components found in better performing MF NCP projects.

Package B: Package A with exhaust air heat recovery in corridors

Package C: Package B with Variable Refrigerant Flow (VRF) heat pumps in apartments

Package D: PHIUS design to meet PHIUS+ 2015

Package E: PHI Team 1 design to meet PHI Standard

Package F: PHI Team 2 design to meet PHI Standard