Josh Salinger describes the evolution of the Phius standard, which adapts passive house design principles to diverse climates in North America, making energy efficiency more accessible without imposing excessive costs. Salinger points out that today’s passive buildings achieve high performance with less material and simpler designs, prioritizing healthy indoor air and resilience against environmental challenges. By integrating best practices in design and construction from the outset, builders can enhance the cost-effectiveness of passive houses, moving beyond outdated perceptions of complexity and expense.

The Passive House Problem

More and more frequently while speaking with building professionals, reading industry literature, and viewing product marketing materials, I am struck by how passive houses are held up as the pinnacle of residential construction—something for other homes to aspire to.

This is great to see, yet there always tends to be a “but” following that statement. This hesitation comes from the perception of a passive house as necessarily containing superthick walls, a complicated origami of control layers, small windows, high-carbon materials, and—as a result—additional and unnecessary costs. And all of this is for the purpose of saving the last possible few Btus of operational energy.

At my firm, Birdsmouth Design-Build in Portland, Ore., we have been building certified passive houses for almost 10 years. This type of building strikes our team as the best science-based approach to delivering high-quality and environmentally responsible buildings that our industry has come up with to date. I have seen firsthand how the passive house approach has evolved over time, and in my opinion, today there is little daylight between any high-quality home and a passive house.

When I hear the aforementioned hesitation, it occurs to me that a lot of folks are stuck in an outdated understanding of a passive house. In North America, we’re now on what I’m calling “version 3.0” of the passive house building methodology. It’s time for our industry to shake the old image and move toward this modern version.

Shared Goals

There are numerous certification sources for what I prefer to call “passive buildings”: the Passivhaus Institute (PHI), Phius (formerly an acronym for Passive House Institute U.S.), the Swiss Minergie standard, and still other variations, some of which have been adopted wholesale by European cities such as Brussels and countries such as Scotland.

Calling them “passive buildings” not only works to encompass the different certification programs, but it also avoids limiting these buildings to just single-family houses, as passive techniques can be applied to multifamily, commercial, and institutional buildings too.

The shared goal is to make our buildings healthier, more durable, more resilient, more comfortable, and more energy efficient through computer-modeled design, airtight construction, minimized thermal bridging, well-installed insulation, and balanced ventilation with heat recovery.

The Phius Standard

We work with the Phius standard, as we see it as the best fit for the diverse climate zones in North America, and this article is written through that lens. Ultimately, what really matters is a building’s impact on society, and our team appreciates that the Phius standard considers not just the site energy (what is read at the electric meter) but also the source energy, which includes all the losses of fuel procurement, electricity generation, and transmission—losses that total up to 70% of the original source energy.

The Phius standard also considers the fact that the electric grid gets cleaner each year with the expansion of renewables. It has adjusted energy targets to be less stringent with successive iterations to account for this. That is a way to meet the carbon-reduction needs of society while not burdening contractors with extra costs for overly robust enclosures that a fixed standard would incur.

Before we jump to today’s passive buildings, however, let’s back up several decades.

A Brief History

Passive building in North America started in earnest in Canada in the early 1970s at a time when energy costs were rapidly escalating and the United States faced an energy crisis with geopolitical roots. Although it unfortunately has a similar name to “passive solar building,” which started in the U.S. as early as the late 1930s, it is distinctly different.

The first passive buildings employed a “light and tight” approach. Avoiding the large expanses of south-facing glass paired with thermal mass that passive solar build­ing was known for, passive buildings favored light-framed walls with great attention to air-sealing and robust insulation.

One of the earliest examples of this is the Saskatchewan Conservation House, which showed that this type of building was more effective and comfortable than the passive solar homes of the day. Designed and built by a team of Canadian researchers, the house was built with rigorous attention to air-­sealing, superinsulated assemblies, triple-pane windows, and an HRV.

It was said to use 85% less energy than average homes of the time. But several factors that arose in the 1980s, including cheap energy and a culture that celebrated consumption (remember the Reagan White House removing the rooftop solar panels installed by the Carter administration?), meant that the desire to build more-efficient homes lost momentum in the U.S. for about a decade.

Meanwhile, in Europe, folks were paying attention to this type of building because of their own reliance on imported and expensive energy. They continued down the passive building path and improved upon it, which culminated with Wolfgang Feist’s creation of the first PHI Passivhaus in Darmstadt, Germany, in 1990.

The next iteration of passive building—version 2.0—landed back in the U.S. in 2003 with the Smith House in Urbana, Ill., and the BioHaus Environmental Living Center in Bemidji, Minn. Although these houses included some technologies that did not prove to be the most effective—earth tubes for space heating and solar thermal water heating, for example—they proved the effectiveness of air-sealing, increased levels of insulation with a focus on mitigating thermal bridging, and strategic siting and glazing orientation.

Low Carbon, High Comfort These clients approached us because they were interested in a high-quality, comfortable building that would have a minimal environmental impact. They hadn’t heard of passive building but were familiar with zero-energy building. After we explained the benefits a passive building would deliver, they were on board. They didn’t see the certification as onerous or expensive. They trusted us and our approach, and after living in the home for over a year now they are full-throated converts. The single-story, 2350-sq.-ft. home was designed with accessibility, low embodied carbon, zero-energy living, and high indoor air quality in mind. It has a concrete-free slab-on-grade foundation. Where we did use concrete, we ordered a 50% slag mix. Above grade, the house is all wood construction with no plastic. Where we needed rigid-foam insulation below grade, we used a low-GWP (global warming potential) XPS product. We used FSC-certified lumber throughout and wood-fiber exterior insulation. For the roof, we chose dropped parallel-chord trusses with a service cavity for running mechanicals within thermal and air boundaries. All the HVAC equipment is in conditioned space. The carbon impact, calculated with the BEAM calculator, was 47,438 kgCO2e—about 20% less than a typical build of this size. Photos: Corey Terril, Ruum Media

The Backlash Begins

Since the standard being used in these second-­generation passive buildings was originally based in central Europe, its landing on North American shores—with our widely varied climate zones—was not perfect. For instance, the BioHaus had 16-in.-thick EPS foam installed below the slab to meet the annual heating demand target in northern Minnesota.

The Smith House had 12 in. of blown fiberglass with 4 in. of rigid insulation on the exterior walls. Many of the passive buildings of this vintage have similarly thick assemblies that required a lot of material to chase the standard. On top of this, there were frequent reports of these homes overheating in the summer, even in those northern climate zones. Also, the one-size-fits-all airtightness metric of 0.6 ACH50 tilted in favor of larger buildings, as this volumetric target made it difficult for small buildings to hit the airtightness goals.

The pushback against the Passivhaus standard culminated in a few hard-hitting articles and presentations that questioned whether the requirements made sense in the U.S. One such presentation was given in 2011 in Olympia, Wash., by longtime Green Building Advisor and Fine Homebuilding editor Martin Holladay, in which he put forth the seemingly sensible argument that we can save a lot more energy by installing 2 in. of rigid foam insulation under seven houses than by installing 14 in. under one house.

A Pretty Good House

On the other side of the continent in Portland, Maine, Dan Kolbert and Steve Konstantino held a meeting of local building professionals in 2011 to discuss building science and high-performance homes. In response to overly designed buildings, the conversations at these meetings were the seeds of a series of blog posts on GBA questioning the sensibility of such building standards, and they ultimately culminated in 2022 with the Pretty Good House book.

At around this same time, Katrin Klingenberg, the founder and executive director of Phius, who built the Smith House, began to question if one static standard made sense in North America. Her home was reaching temps of near 100°F in the summer, so clearly there was something amiss.

Klingenberg said, “Using [the 2.0 version of] heating demand in California climates that have none was like building a fence sized for cows around chickens—lots of savings remained on the table.” Not to mention that the modeled vs. measured data of these projects was consistently off by 25% to 30%.

Lisa White, the co-director and a technical lead for Phius, said, “In general, we have found that not making targets climate specific can lead to issues such as overheating and discomfort. This can also guide overinvestment in some measures, which may seem harmless but directly correlates to additional up-front emissions and could often be invested in other decarbonization strategies.” It is at this point in history where I believe a lot of people simply got stuck. But things weren’t done evolving.

Iterative Changes

In 2015, Klingenberg and her staff partnered with Building Science Corporation under a U.S. Department of Energy grant to create an affordable, climate-specific standard with passive building principles, which became known as the PHIUS+ 2015 Passive Building Standard. Thus began the era of passive building version 3.0.

The goal was to correct the historical problems with passive buildings in North America by adjusting the size of the fence to fit the climate where the building was to be located. If the house was to be in the northern reaches of Minnesota, the “fence” would be bigger than if the house were in San Diego.

Keeping Up with Updates

Similar to how the International Residential Code (IRC) is updated every three years, the Phius protocol also kept changing with new information and feedback, which led to the PHIUS+ 2018 and Phius 2021 standards, and the current Phius 2024 standard.

Each successive standard is corrected and adjusted with new information and insights, with the goal of creating the most cost-­effective way to reach a zero-energy and zero-carbon built environment. Meanwhile, the International Energy Code Council has been making iterative changes in energy efficiency every three years.

These codes end up in the IRC, and if you follow this progression, it points to the energy code reaching parity with passive building in about two or three more code cycles. If the energy code meets passive building levels, then what is the point of the standard?

In one way, this would be great—mission accomplished! But passive building is primarily about durability, health, resiliency, and comfort—in that order. Energy efficiency is a happy side effect. As I have been prone to say, any knucklehead can build a zero-energy home, but it needs to be done so that it doesn’t rot and create mold and unhealthy indoor air quality.

This is where the Phius standard and the robust building science behind it will likely continue to endure.

Resilience, Forever This client hoped to build a forever home that would require little maintenance while being resilient enough to withstand the frequent power outages common to the rural area. The client, an engineer well versed in building science, thought a passive building would be overbuilt and expensive. I explained that an uncertified, high-quality home might have the same assemblies and systems as a passive building without the benefit of third-party quality control. He warmed to the idea, helped by the fact that we could pay for certification through incentives. The two-story, 2600-sq.-ft. home was built on a concrete-slab foundation insulated with 4 in. of low-GWP XPS foam. The wall assembly is 2×6 framing at 24 in. on-center with dense-pack cellulose insulation. The ZIP System sheathing is covered on the exterior with 1-1⁄2 in. of cork insulation. Both cellulose and cork are carbon-sequestering materials; cork also helped us achieve a fire-rated assembly (the home is in the wildland-urban interface). The truss roof is also insulated with cellulose—R-43 in the vaulted ceilings and R-60 in the flat ceilings. The innovative HVAC system was engineered by Energy Vanguard and combines a Minotair all-in-one ventilation, filtration, and heat-pump unit with auxiliary heating from a SanCO2 heat-pump water heater and a heat exchanger installed on the supply duct. A rooftop 8.4kW solar PV system gets the house to net-zero energy use annually. A standby generator provides uninterrupted power when the home is disconnected from the grid, which happens a few times each year.

Today’s Passive Building

Instead of fixed heating, cooling, and energy targets no matter where a building is located, and instead of a static 0.6-ACH50 airtightness metric no matter how big, small, or articulated a building may be, the latest Phius standard considers a number of factors that are entered into an online calculator to determine the heating, cooling, and source-energy targets.

The airtightness metric is no longer a volumetric measurement but is instead a ratio of enclosure area to leakage. This equalizes all buildings, large and small, as it becomes a percentage of allowable leakage. Simply enter the type of building, be it residential or commercial; the form of the building (a ratio of enclosure area vs. conditioned floor area); the number of dwelling units; the number of bedrooms; and the exact geolocation of the project, typically determined by the nearest weather station. The calculator then spits out custom heating and cooling targets per conditioned square foot and the allowable amount of source energy per person per year.

Tangible Change

This is all pretty technical stuff, but in terms of real-world impact, we can now determine where another 1/2 in. of insulation isn’t worth the cost, resulting in a building designed to hit the elusive intersection of energy efficiency and cost-effectiveness. Our team’s last three certified projects illustrate this point well when compared to the passive buildings that were produced in the 2010s.

Instead of 16-in.-thick walls, we’ve been regularly meeting project goals with 2×6 walls with 2 in. of exterior insulation. The revised airtightness requirement for these roughly 2500-sq.-ft. buildings is closer to 1 ACH50, which we’ve been able to hit without difficulty.

Ultimately, a passive building delivers comfort, durability, and healthy indoor air. It offers resilience against cold snaps and their associated frozen pipes and water damage, and against heat domes with their terrible effects on at-risk communities. It also delivers comfortable interiors that keep people from throttling their thermostats, and therefore fosters energy efficiency.

This is done with energy modeling, airtight enclosures, mitigated thermal bridges, high-quality insulation, and balanced fresh air delivered with heat recovery. What I just described is no different from a high-performance house or a Pretty Good House.

You wouldn’t slope the grade toward the house, skip kickout flashings, or not use a fully ventilated rainscreen—these are all best practices. Quality is delivered through best practices, and passive buildings are simply a collection of best practices from design through building and commissioning.

The good news is that the program has also evolved to be easier to work with. There are now mature passive building organizations, great opportunities for training and education, high-performance products and mechanicals, and readily available air-sealing and assembly details, along with a burgeoning knowledge base in the industry that is willing to share tips and lessons learned.

Real-World Examples

The absolutely critical key to unlocking cost-­effectiveness in passive building is to start with this methodology in mind during design. Ideally this is done with a design-build approach, but at a minimum it includes the entire team at the table from the beginning: the architect, the builder, the energy modeler, the engineer, and the mechanical contractor/consultant. To take any old design and try to wedge it into passive building compliance is a fool’s errand and will simply perpetuate the idea that this type of building is expensive.

Aesthetics are important. After all, an ugly building won’t be cherished or maintained and may even be taken down before its life­span has come to pass. With good design, aesthetics and performance can be complementary. The passive building shown above is a good example.

Making Energy Efficiency Look Good

The goal with this home was to create a simple thermal enclosure but maintain a compelling aesthetic. It is simply a box with one top corner clipped off. But look at the finished home and you will see a garage that is set back from the main home’s massing, two separate elevations for the roofline, a covered front porch, plenty of windows, and a balcony overlooking the river.

This home was affordable for our clients, responded to the site, met the clients’ aesthetic wishes, and generates zero energy bills. Because it is in the wildlife-urban interface (WUI), the home also has fire-resilient materials, including 11/2 in. of Class-A fire-rated cork exterior insulation over a 2×6 wall.

We were curious if the home would have met the Phius standard without any exterior insulation and just a 2×6 sheathed wall, so we modeled it; with an upgraded window package, it would have. The home is in a Goldilocks climate zone (4C), but with good design the premium doesn’t need to be excessive by any means.

Another one of our passive buildings, shown above, is similar in that the client’s goal was a modern farmhouse aesthetic with a single-story, aging-in-place design. We were able to simplify the footprint of the home and embellish it with gable trusses set perpendicular and offset from one another with an attached breezeway and garage to create interest while leaving the thermal enclosure as a simple “T” shape.

This resulted in a 2×6 wall with 2 in. of exterior insulation. This house needed only a 9000-Btu heat pump to keep it at 70°F on the coldest day of the year and was able to withstand a two-day power outage during an ice storm while maintaining full use of the home’s functionality due to battery backup power. This demonstrates resilience in action.

Doable Details If passive building programs are known for one thing, it is their high expectations for air-sealing. And even with a more flexible target for today’s Phius-certified houses, airtight construction still is part of the program. Once you get your head wrapped around a few important details, however, it’s just not that hard. Two places where houses tend to have big air leaks are where the concrete foundation meets wood framing, and where walls meet the roof. In these locations, we have adopted foolproof details that are common in passive buildings. Simple and quick solutions like these can put a house within striking distance of the Phius airtightness metric. We have been doing this for so long that it has just become a part of our muscle memory, and we consistently hit the airtightness goals on our first blower-door test without feeling like we have put much effort into it. Photos: courtesy of the author.

Incentives Can Cover Costs

Of course, certification with any program has costs. But these costs bring value and often come with incentives through federal, state, local, or utility programs. There are numerous states that offer incentives for certifying a passive building. Here in Oregon, we were able to capture almost $11,000 of incentives for the house.

The certification fees were a little over $3000, and we spent a total of 32 hours of back and forth with Phius during the certification process, which totaled almost $4000. So, we came out ahead by close to $4000 on this project.

Certification has other benefits. As a prerequisite, Phius requires compliance with the U.S. DOE’s Zero Energy Ready Homes program, the WaterSense program, the Indoor Air Plus program, and the Energy Star program. All these programs are intended for the final occupant’s health and safety while being energy and water efficient.

Performance-Based Standards

We don’t just want to boast to our clients that we are building the highest-quality home possible. We want to have a third party check our work at various stages during the design and building process to prove it and hold us accountable.

One of the great things about passive building is that it is a performance-based standard, meaning that we can build it however we want, but it must be tested to prove it meets the targets. I really haven’t had a hard time selling this to clients within that framework, especially since we offer to cover the costs of certification, as we know we will be getting the money back and then some through the local incentive programs.

Ever-Evolving

It is also true that passive building has a learning curve. Paul Eldrenkamp, the founder of Byggmeister Design-Build in Newton, Mass., has said, “There are two types of passive house projects: your first one, and all the rest.” I couldn’t have found this to be more true.

Now that the last five homes we have built have been certified to the Phius standard, our field staff has internalized this way of building and often questions what was so hard about it the first time. At this point it has become just building for them.

We have found that once you learn how to do something right, and if you are a reasonable human, you cannot go backward and do things you know to be wrong. It is time for us to move forward as an industry and jettison this antiquated idea of what a passive building is. As Yogi Berra once said, “The future is not what it used to be.”

— Josh Salinger is the owner of Birdsmouth Design-Build in Portland, Ore.

From Fine Homebuilding 328

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