Passive House Murder Mystery Part III: Passivhaus Becomes Phius

This blog is part of the Passive House Murder Mystery series. Read Parts I and II here. 

The adoption of the German-developed passivhaus model in the US starts in earnest in 2003 with the founding of the Ecological Construction Laboratory, a community housing development organization. Under it, following my house built in 2002, we designed and built a total of three affordable homes in Urbana, Illinois. In 2007, the Passive House Institute US is formed with the intention of providing passive building education and research. The first professional trainings are delivered around the country and Canada starting in 2008. Both entities merge in 2009. 

In 2005, a female architect from New York City kept calling our office. She was trying to get me to come to a conference in Boston to present on my house that I had built in Urbana. She was putting a “passivhaus” panel together after she had traveled to Europe. I was busy and had work to do (we were working on our affordable developments at the time). Boston? Who? Where? Why? It turns out that architect was none other than Chris Benedict, and she would not give up until I finally gave in. 

In 2006, we took a road trip out to Boston to attend and to present at my very first North East Sustainable Energy Conference (NESEA). I was matched up with Marc Rosenbaum, a mechanical engineer and high-performance pioneer from the early passive house era in the US, who had studied my house beforehand (there had been an early publication titled ‘An Illinois “Passivhaus”’ in the Energy Design Update in 2004). He ran a comparison to his Hanover House. Chris had thrown me in on the deep end with the North American experts, who I had no idea existed at the time. 

The next panel had Betsy Pettit and John Straube from Building Science Corporation on it, discussing the feasibility of the German concept for North America. Henry Gifford gave an impromptu introduction to humidity issues using his psychrometric T-chart. It was a memorable way of being introduced to people who would soon become my mentors, friends and highly respected and admired colleagues. We, as in Phius, have attended and presented at NESEA ever since and became an integral part of that community. In 2022, I was thrilled and honored that NESEA awarded me the Professional Leadership Award, joining an illustrious group of experts, many I have long admired.

Keenly aware of North American history and those who came before us, we decide to go back to using the original English term “passive house” rather than the German term “Passivhaus.” We continued to work with the German Institute until 2011 on mostly single-family homes. By then, we had fully certified about 10+ homes under their program in various parts of the US and a duplex in Toronto, Canada with another 15 in progress. At that point, we had collected enough evidence to conclude that the one-size-fits-all methodology and the accompanying design tool is not leading to optimal results in the varied climates of North America. 

Building typology, size and density are critical factors that must influence the design target setting in order to guide and deliver optimal design solutions for thermal comfort and total carbon (operational and embodied) and to avoid over-investment in the envelope (for cost and carbon reasons). 

While still applying it, we learned all the lessons our European counterparts had learned before us and more. One new revelation came from measured data: the internal gains assumed in the German design tool PHPP were nothing compared to what was known to be the norm in North America. With internal gains severely underestimated, measured heating was significantly higher than the model had assumed. Thus, the total energy consumption was regularly approximately 30+% underestimated. Cooling predictions did not match at all. The design methodology and model predictions simply did not hold true.

In addition, hygrothermal challenges were everywhere – in cold, mixed and hot climates as wall assemblies had to change according to climate. There was no design guidance on how and why it was important to change wall assemblies based on climate to avoid mold. It was obvious: the German-derived targets were, in most climates, not leading to optimized designs, and they could put people and their significant investments at risk. 

Marc Rosenbaum showed up for our first training on the "passivhaus" methodology in 2008 and immediately asked the obvious question: “Why 15? Why everywhere?” I was stymied by his question. At the time, I had no good answer. I hadn’t really understood yet where the targets actually came from and that they were specific to Germany’s climate.

I personally learned a few things in my house (beyond the obvious of the blown relay of the ventilation integrated heater and mismatched peak load). I learned about humidity the hard way. Earth tubes, while perfectly fine with no condensation in the non-humid European climate, do not fare as well in the continental humid climate of Illinois. My 8-inch, 100 ft long earth tube dehumidified brilliantly and filled up with fresh water by July and started gurgling (I am in swamp land, due to a very high water table I was not able to have a drain installed at the negative 6 ft low point). From then on out I was pumping loads of fresh clean water – drought solution anyone?

On cooling: the house overheated like crazy during the summer despite very few and small low solar heat gain windows on the East, West and North facades and almost total shading on the South. Natural ventilation was only possible during a couple of the coolest hours of the night (when I was sleeping) and provided little relief, because the temperatures did not drop enough and the air would be loaded with humidity. It was a tough choice to make – bringing in a few degrees cooler temperature in exchange for the mother load of humidity that came with it. I needed cooling and dehumidification badly –  it was very uncomfortable. 

The house also overheated in the winter, but then at least the air was dry and very cold so I could open the windows to cool off. Overheating relief during the shoulder months, especially in spring, was more difficult, as the humidity would rise quickly early in the year. It was a few very uncomfortable years trying to live passively within the 10% of overheating the PHPP had promised me until I finally gave up and retrofitted an appropriate, minimized mechanical system that included dehumidification and cooling.

After a particularly bad experience with a project in a challenging hot and humid cooling-dominated climate, we concluded that the one-size-fits-all targets really needed fixing and serious quality assurance is necessary to make sure things actually worked and to keep people comfortable and safe. At that time, only the need for climate-specificity became apparent to us and that we had to deal with the cost structure in the US to keep insulation investments from pushing into diminishing returns.

Later, as we started certifying bigger buildings (as their design is internal load dominated), we also understood that building size, typology and density were an entirely different ball game yet again. Cooling and dehumidification were the governing design conditions, while heating was very small and almost irrelevant. The name of the game was not as proclaimed under the German standard – to keep the heat in with superinsulation (very wrong focus for big buildings) – but how to shed it. It was all about the right balance of high-performance measures. More was not necessarily better; it made the cooling case worse. And to get to that balance point different targets were clearly needed. Specifically, more precise targets based on the unique conditions to guide heating and cooling were needed. 

The solution was clear: building typology, size and density are critical factors that must influence the design target setting in order to guide and deliver optimal design solutions for thermal comfort and total carbon (operational and embodied) and to avoid over-investment in the envelope (for cost and carbon reasons). It did not make sense to use design targets and tools for large buildings in varying climates that had been developed for an end townhouse in the moderately heating-dominated German climate.

Long story short, in 2012 we decided to leave our agreements with the German Institute behind and partnered with the US Department of Energy (DOE), the Residential Energy Services Network (RESNET) and Building Science Corporation (with principals Dr. Joe Lstiburek and Betsy Pettit) instead.

With them, we went on to develop the first and still only climate-specific, cost-optimized passive building standard. The methodology was published in 2015 as part of the Building America Program by NREL after intense peer review. That work became the foundation for developing the new Phius Passive Building design guidance and building certification program. Our monitored projects became proof of concept for the US. Excellent evaluation and documentation of performance and construction cost from third parties confirmed our premise – it is now available from a MassSave competition for eight projects in Massachusetts and NYSERDA's Buildings of Excellence Program for a much larger batch of projects. Two more updates to our new Phius Passive Building Standard followed in 2018 and 2021, which finally incorporated factors such as building size and density.

But our story doesn’t end there. We had proof of concept, but there was a long road ahead before we reached our ultimate goal: making passive building mainstream. Find out more about our strategy to revolutionize the building construction sector in Passive House Murder Mystery Part IV.