Passive house history (PHistory) Part I–North American roots

In 2002, when I set out to build my own passive house as a proof of concept, I eventually selected a site in Urbana, Ill. I had was working in Chicago at the time, but Urbana made sense for several reasons: it offered affordable land, the city and its citizens have a progressive history in terms of environmental issues, and it is home to the University of Illinois at Urbana-Champaign (UIUC) and all the resources that a research institution offers.

What I’ve learned since then is that pioneering work at UIUC decades ago actually helped spawn what we now refer to as passive house. It’s a fascinating history, and one worth sharing here. To all the pioneers out there—weigh in with additions and clarifications. I hope you enjoy!


Passive house describes a set of design principles and defined boundary conditions that—if applied holistically—lead to a building that remains comfortable with only minimal active heating or cooling during extreme climate conditions. The specific boundary conditions determine the design of the thermal envelope. Minimized mechanical systems result from specific space conditioning energy consumption and peak loads: quantitative, measurable performance-based energy metrics for homes and buildings.

The underlying passive principles were pioneered and formulated in the United States and Canada in the 1970s and 80s following the oil embargo and resulting energy crisis of 1973. By 1986 the noted physicist William Shurcliff was able to summarize what at the time he considered a mature and widely adopted technology. He described the five main principles of superinsulation also known then as passive housing in his article int the 1986 Energy Review”:

a) thick insulation
b) airtight construction
c) prevention of moisture migration into cold regions within the walls, and other regions where much condensation could occur
d) optimum sizing of window areas
e) a steady supply of fresh air

He goes on to describe in detail the necessary components: triple pane windows, heat recovery ventilators, thermal bridge free and airtightness design strategies, vapor retarders, a small wood stove as a heat source for the entire house etc.

In essence, what Shurcliff termed “Superinsulation” was essentially identical to passive house as we know it today.

Council Notes–the University of Illinois’ Small Homes Council periodical–featured the Low-Cal house back in 1981. Plans and energy modeling details were published in a standalone paper years earlier.


Where it started: Back to the future

Urbana, Illinois. The same Urbana that—by Kismet—is today home of PHIUS. In the early 1970s, a group of engineers and architects at the University of Illinois Small Homes Council (now knows as the Building Research Council) began experimenting with highly insulated envelope components. The group included included Wayne Schick (who coined the term superinsulation), W.S. Harris, R.A. Jones and S. Konzo. Their research culminated in the concept of the Lo-Cal (for low-calorie) house in 1976. (You can still buy original publications about Lo-Cal by the Council and Schick  here. And Building Science Corporation’s Joe Lstiburek writes about it here.) Lo-Cal was projected to save 60% in energy consumption compared the most efficient design promoted at the time by the Department of Energy.

A young architect working with the Council at the time, Mike McCulley, built four Lo-Cal houses in Urbana and Champaign. The Council monitored and evaluated them for performance, and these projects gained some attention from press outlets around the country.

An article about one of McCulley’s Lo-Cal houses appeared in the 1982 Louisville Courier-Journal. (Click to enlarge)

This Illinois group’s ideas greatly influenced a Canadian group of engineers working on the Saskatchewan Energy Conservation House (well chronicled in 2009 by Martin Holladay in Green Building Advisor–“Forgotten Pioneers of Energy Efficiency). They succeeded in reducing losses and peak loads even further. The peak load of the Conservation House in this extremely cold climate was designed to be approximately 1.5 W/sqft, equivalent to the best peak loads we are seeing in today’s passive houses in similar climates.


The concepts gained momentum in both countries, spawning prototypes and buzz at building conferences.  The press and the public took notice. The term superinsulation was evolving as the most commonly used label for this set of principles in a growing North American high performance building community.

In 1980 William Shurcliff published one of the first books on the topic, called “Superinsulation and Double Envelope Houses.” Shurcliff, an accomplished physicist who took up the subject after his retirement from Harvard, went on to publish many books on the passive solar and superinsulation concepts in the late 1970s and early 1980s. In fact, Shurcliff appears to be the first to have labeled the new concepts “passive house” in his 1982 self-published book “The Saunders-Shrewsbury House” [Shurcliff, 1982]. It describes direct-gain and indirect gain passive houses. Later in a 1986 article he states that “a superinsulated house is really a special type of a direct-gain passive solar house.”

Because many architects and builders felt that superinsulation was too narrow a term, passive housing started to be commonly used interchangeably with “superinsulation.

Regardless of labels, Shurcliff states that by the mid/late 80s there were tens of thousands of homes built in the United States and Canada (as many as in Europe today!) to these design specifications. By 1982 a movement had formed. Thousands of building professionals were traveling to conferences taking training to learn the techniques. Construction of such homes was growing “explosively” as Shurcliff puts it in one of his early books in 1980 (Superinsulated Homes and Air-to-Air Heat Exchangers). The Canadian government offered free builders trainings. Widely read magazines sprung up, amongst them the still today well known and respected Energy Design Update.


Shurcliff defined a superinsulated house as follows: “…a) receives only a modest amount of solar energy […], and b) is so well-insulated and so airtight that, throughout most of the winter, it is kept warm solely by the modest amount of solar energy received through the windows and by intrinsic heat, that is, heat from miscellaneous sources within the house. Little auxiliary heat is needed: less that 15% as much as is required in typical houses of comparable size built before 1974.”

He further explained: “The 15% limit on auxiliary heat […] was chosen because a house that conforms to this limit can get through the winter fairly tolerably even if auxiliary heat is cut off entirely. Specifically, the house will never cool down to 32 F. […] In summary, the basic strategy of superinsulation is to make the house so well-insulated and airtight – so conserving of heat – that it is kept warm almost entirely by heat that is received informally and is free.” (2)

What’s striking is that the 15% maximum limit cited for the annual heating demand compared to standard construction at the time is very close to the energy metric that defines today’s passive house criteria: 4.75 kBTU/sqft yr!

To explain: Comparing current contemporary home energy consumption for heating to the energy consumption of a home built in 1970 one finds that the reduction in heating energy consumption from 1975 to 2006 is approximately 17% (see DOE graph). In 2005 a typical home in the state of NY consumed approximately [34.76 kBTU/sqft yr] according to the EIA for heating. Increasing this energy consumption by approximately 20% (MEC-IECC Graph) results in 41.71 kBTU/sqft yr for a home built in 1974 (before the MEC took effect). 15% of that total value equals 6.25 kWh/sqm yr, (19.7 kWh/sqm yr) an energy metric limit very close to the current Central European passive house metric of 4.75 kBTU/sqft yr which was codified in the late 80s to early 90s.

Note that most passive houses at the time were built in quite a bit colder climates of the US and Canada. The colder climate boundary conditions are likely reflected in this slightly higher annual heating demand limit (as a direct result of greater peaks).  Peak load then as it is today was understood to be the determining factor. Another curious historic trace of those early superinsulation experiences describing very low load homes similar to the European secondary passive house standard peak load threshold of 10 W/sqm exists in the International Energy Conservation Code (IECC). The current International Energy Conservation Code (IECC) still recognizes extremely low load homes, defining them as homes with a peak load equal or smaller than 1 W/sqft (10 W/sqm) for heating in section 101.5.2 [International Code Council, 2012] effectively exempting them from having to have a conventional auxiliary heating system. The code assumes in this case that the intrinsic heat sources are equal to the tiny peak losses aka no need for additional heat. According to the Code Council the IECC is the successor of the first 1975 Model Energy Code (MEC), from which this definition was originally adopted!

Shurcliff goes on to describe the performance of such houses in winter:

“1. The typical annual heat requirement on the auxiliary heating system is so small that the annual cost is almost negligible compared to the main household expenses […] 2. The occupants benefit from the absence of drafts, cold floors, and cold spots near windows. 3. Because the south windows are of modest size, little or no sunny-day overheating occurs. 4. Anxiety as to possible failure of the auxiliary heating system is minimal because the rate of cool-down is so low (a fraction of a degree per hour) that the house can easily ride through a 24-hour period with no auxiliary-heat-input. 5. Thanks to the use of an air-to-air heat exchanger, humidity tends to remain in the desirable 40-60% range and there is a steady inflow of fresh air (at, typically, 50-150 CFM, or about half a house volume of fresh air per hour). 6. Little outdoor noise penetrates the house.”

He also notes that the orientation of the house is not critical to the concept. He says that the house can have almost any orientation, unlike only passive solar-heated designs that had to be oriented within 25 degrees of south.


The technology matured and the market began to follow. Energy Design Update published an entire edition in 1987 as a consumer guide devoted solely  to the many air-to–air heat exchangers. The Canadians appear to have taken the technology lead in the 1980s. Shurcliff credits Harold Orr’s construction type from the Division of Building Research of the Canadian National Research Council to be the most widespread type being built in North America.

In 1984 young J.W. Lstiburek and J.K Lischkoff publish a book called “A New Approach to Affordable Low Energy House Construction,” further advancing various aspects of passive housing and related sciences. The “Superinsulated Home Book” by Ned Nissen and Gautum Dutt published in 1985 is the most advanced construction and detailing book in the industry at the time. The book even presented a detailed chapter on the theory of energy balancing and sample calculations for low load homes, explaining how to balance losses and gains to arrive at a design with an extremely low balance point temperature.

In 1988 Shurcliff concluded in his book “Superinsulated Houses and Air-To-Air Heat Exchangers” [Shurcliff, 1988] that this type of energy efficient home construction is here to stay and that one might see some further improvements in window technologies, vapor retarders, more efficient heat exchangers and compact minimized mechanical systems, “…but that there is no need to wait for such refinements. Superinsulation is already a mature and well proven technology.”

That was 1988, and the future of superinsulation/passive housing in the United States was bright, but…

See the passive house history Part II





Ten years after

Hi folks, this is Mike Knezovich, also known as Mike #2. (PHIUS has a Mike problem.) I pitch in here on communications, conference, and, like everyone does in a small organization, whatever might need done. Anyway, Katrin’s in Pittsburgh for CPHC training at CMU, and is loaning me the Klingenblog space to wax a little nostalgic. Hope you enjoy.

A little more than 10 years ago, my wife and I took a frigid winter walk from our vintage (as in older than dirt) house in Urbana, Ill., to a little downtown bar called The Embassy. A good band was playing that night, and the place was packed. Friends waved us over, and in turn introduced us to their friends from out of town, and invited us to sit with them.

Raising the TJI-framed walls for Smith House.

One of their visiting friends was Katrin Klingenberg, an architect who lived and worked in Chicago. She had this idea to build a proof of concept for something called a passive house and was scouting for an empty lot–knowing land would be a lot more affordable in East Central Illinois than Chicago.

I was editor of an alt-weekly newspaper in town and started grilling Katrin. With healthy skepticism. But she wasn’t talking pie-in-the-sky bleeding edge technology like a magical yet-to-be-developed hydrogen fuel cell that would sit in the back yard.

Superinsulation. Airtight envelopes. Energy recovery ventilation. Triple pane windows. Passive solar. I’m a journalist by training—building science ain’t my forte. But I understood this stuff. And I figured if it made sense to me, it probably would make sense to a lot of other people, too. And that this might be a great story. I got Kat’s card, and later, when she and her crew got the slab for Smith House in the ground, I attended the groundbreaking party, and I got a nice feature for my paper.

During the summer months, vegetation on the trellis provides nice shading.

PHIUS staff celebrated the 10 year anniversary of the groundbreaking for Smith House just last week with an autumn cookout. And it brought to light just how much has changed in 10 years.

Urbana is now home to seven passive houses, three of them affordable housing projects built in partnership with the City of Urbana. More than 800 folks have taken the PHIUS CPHC training, with better than 400 earning CPHC status. Dozens of projects have been certified, and more than a hundred are in the pipeline.

Established institutions—like the U.S. Department of Energy, RESNET, Building Science Corporation and Fraunhofer IBP—that once were as skeptical as I was about passive house now see the value.

Years after writing the newspaper story I was recruited to the Ecolab and later the PHIUS boards. And a couple years ago, I joined PHIUS –at that time PHIUS was founders Katrin and Mike Kernagis, plus Ryan Abendroth — at PHIUS as an employee. Since then it’s been a ride.

I was lucky back in the 90s to have a front-row seat at the birth of the Web; I see definite similarities.

A peak inside from the loft.

Technologies once reserved for elite technocrats being democratized. Tremendous excitement. Constantly changing technology and changing assumptions. A feeling of infinite potential alternating with fear of losing steam. New players. Intense passion and competition. A need for open, adaptable standards and technologies that will help accelerate—not impede—growth.

During our conference in Denver, the sense of busting out was palpable. Passive house principles are on the verge of going from being a boutique program with a cultish following to something that will soon be commonplace. I feel proud and privileged to be along for the ride.

Thank you all for continuing to push. And though I can’t design or construct buildings, I’ll do my small part. I mean, I know a good story when I see one. And I think this one’s just getting started.

Mike Knezovich