The Evolution of Passive House in North America

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In 2002, Katrin Klingenberg introduced the passivhaus program to North America when she built the Smith House in Urbana, Illinois. She had come to the US from Germany, where she studied architecture and got involved with passivhaus. But is this really where it all began?

Of course it's not. The Passivhaus program, promulgated by the Passivhaus Institut in Germany, formalized the requirements but was building on earlier work, much of it from North America. Even the term "passive house" has American origins.

Here are three of the early superinsulated houses in North America:

  • Illinois Lo-Cal House, 1976. Lo-Cal here is short for low calorie, as in low energy. That's a sketch of it above and a vertical wall section below. Notice the double-stud walls and triple pane windows. This was the beginning of superinsulated houses.
  • Saskatchewan Conservation House, 1977. Another superinsulated house, this one with R-40 walls, R-60 roof, triple pane windows, and extremely airtight.
  • Leger House, 1977. And a third, this one in Massachusetts.


But were they "passive houses"?

William Shurcliff was a Harvard physicist who worked on the Manhattan Project in World War II, helped stop supersonic passenger planes in the 1960s, and took a big interest in passive solar and superinsulated building in the 1970s and '80s.

In 1979, he put out a press release praising the characteristics and benefits of superinsulated houses. He described the thick insulation ("Not just thick, but clever and thorough"), the airtightness, the lack of a need for thermal mass and large, south-facing windows, and the ease of controlling temperature and humidity.

He concluded his press release with this:

"What name should be given to this new system? Superinsulated passive? Super-save passive? Mini-need passive? Micro-load passive? I lean toward ‘micro-load passive.’ Whatever it is called, it has (I predict) a big future."

Martin Holladay resurfaced this piece of superinsulation/passive house history in his 2009 article, Forgotten Pioneers of Energy Efficiency on Green Building Advisor and republished nearly the entire piece. Go to his article to read that and more on this topic.

The evolution of passive house

Shurcliff's preferred term, micro-load passive, didn't catch on, but the passive part did. Those "forgotten pioneers" also pushed another piece of the passive house concept. They understood that airtightness and energy efficiency were important. That meant quantifying the goals, setting limits for annual and peak loads.

Dr. Wolfgang Feist, a German physicist, and Dr. Bo Adamson from Sweden took those early ideas and created the Passivhaus program. In their program, certification required hitting an annual load at or below 4.75 thousand BTU per square foot per year or a peak load of 3.17 thousand BTU per hour per square foot. They also have to achieve an airtightness of 0.6 ACH50 or less and a primary energy of 38 thousand BTU per square foot per year.

That's what Klingenberg learned in Germany and brought with her to the US. Those numbers worked great in Germany but not so well in all parts of the US. There were problems with the insulation required in really cold climates like Minnesota and with cooling and dehumidification in places like Kentucky and Louisiana.

So the Passive House Institute US (PHIUS), of which I'm a board member, developed new climate-specific passive house standards. Instead of one set of numbers for every place in the world, we have numbers that came out of a lot of work by Building Science Corporation and others on what numbers are supported by the science for different climates in North America. PHIUS also has a rigorous quality assurance program called PHIUS+ Rater, using HERS raters to verify homes going for certification.

The split between PHIUS and PHI

Unfortunately, relations between PHIUS and PHI came to an end a few years ago. I wasn't involved at the time and don't know all the details, but now there are two separate groups promoting passive house in North America. The North American Passive House Network (NAPHN) was created after the split between PHIUS and PHI. They promote the German standard. Passive House Institute US now has gone its own way, with a variation of the German standard.

Both groups have their own conferences. I attended the NAPHN conference in New York City a couple of weeks ago. It was well attended (about 500 or so) and had a good trade show. I got to see some old friends and meet some IRL for the first time. (Hello, Terry!) There were also quite a few people there whom I know from PHIUS conferences.

In September, PHIUS will host its 10th anniversary North American Passive House Conference. It's in Philadelphia, and I'll be giving a presentation there on a topic that's gotten me in trouble once already this year. The title is The Global Warming Impact of Insulation Revisited. Joe Lstiburek will be there again, of course, as will Marc Rosenbaum and a bunch of other smart people. (And if you register by 18 July, you can be there, too, and get the early bird rate.)

What's next?

There you have it. Forty years of evolution of the passive house concept in North America, including a trip across the pond and back. Where it goes from here remains to be seen. There's some confusion in the marketplace because of having two groups and two different certification paths. (I'll write more about that in a future article.) Naturally, since I'm on the PHIUS board, I have a bias. I think anyone going for passive certification on a project should go through PHIUS's climate specific standards and PHIUS+ quality assurance.

A lot of others do, too, because PHIUS has more than a million square feet of buildings certified and pre-certified. When you add the projects that have been submitted but aren't yet pre-certified, that number jumps to about 2.5 million square feet. The big driver isn't single family detached homes, though. It's big multifamily projects.

Come to the 10th anniversary North American Passive House Conference in Philly to learn more about passive house. Will I see you there?


Related Articles

On the Edge: The North American Passive House Conference

Passive House — The Only Place Where Real Innovation Is Happening?

Dr. Joe Lstiburek Surprises Passive House Conference Attendees


Outside Resources

Forgotten Pioneers of Energy Efficiency, by Martin Holladay (GBA)

The History of Superinsulated Houses in North America, by Martin Holladay (GBA)

Passive House Institute US (PHIUS)

North American Passive House Network


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David Eakin

The original standard could still work, with 2 changes. Add "maintaining an inside relative humidity between 45-60 percent" to the air quality section, and convert the Btu/square foot per year measurement to kwh/square foot per year (to address air conditioning/dehumidification load) in addition to heating load.
Now if only this standard would catch on with architects, builders and code enforcement officials - as well as the US Department of Energy. Of course it's only been about 40 years and these things take time... What gets me is all the "opportunity costs" - all the millions of homes that have been built in 40 years that will still be around for 60 or more years - all with poor performance unless (expensively) retrofitted. So much easier (and less costly) to do it well initially.

John Nicholas

David, Why 45-60 on RH? ASHRAE 55 calls for 30 - 50. My home has been fairly constant the last 4 weeks at 40% +/- 2 with 75% RH Ambient. CZ 4 Mixed Humid and an ERV. Most folks are dialed in on the above 50% being a problem

I think part of the 40 year history is that the Passive Concept has be a niche market. Either highly motivated or DIY types. The activity in the multi-family area is a big boost. It will get exposure and those living in those apartments will not want much else when they buy a home.

Donald Endsley

John, ASHRAE 55 is mostly concerned with human comfort, not necessarily human health. A RH of 30-50 gives a high range of temperatures where humans are comfortable doing a high range of activities.

Human health, especially due to respiratory issues, seems to be best at around 50% RH.

John Nicholas

Do you have a citation for the Healthy connection with around 50%?

David Eakin

John - Krigger/Dorsi recommend less than 60% to preclude mold issues; several studies on what a minimum RH should be to preclude dry sinuses; Robert Bean's site says that humans can tolerate a fairly wide range of RH depending on temperature. I just picked 45%-60% interior RH as a workable range. FWIW - one of the assumptions in the Passive House design parameters that is not easy to dig out is what the interior temps are supposed to be (lots of talk about energy use, emissions, and cost but not interior temps or assumed comfort). Found some data in a slide presentation talking to the North American climate diversity and needed changes to the PH standard: 68 degrees for Winter and 77 degrees for Summer - but I'm not sure if this is truly a set design factor in the software or just a working recommendation. Would like to hear more from folks with experience in PH design as to planned interior temp and RH ranges.

Kent Lessly, RA, CPHD

Hi David,

The design metrics for Passive House that you most frequently hear about are quantification of the energy performance and air-tightness necessary for achieving Passive House Certification.

However, the central design criteria for a Passive House is comfort. Everything revolves around that. So the beautiful thing about the Passive House design standard is that you won't be making draconian sacrifices in comfort to achieve the predicted energy savings. You'll also find that excellent indoor air quality is another important criteria that the standard adheres to. These are considered"soft criteria" as they are not enumerated specifically but taken into account in the modeling software and are achieved when a compliant design is achieved.

Ultimately, the temperature settings are up to the occupant and therefore, to a degree, so is the energy savings. But if you want to achieve the precise level of energy performance predicted by the Passive House Planning Package (PHPP - the energy modeling software for International Passive House design) those are the settings. 77 degrees F may seem a bit high in the context of standard construction here in the US, but with lower indoor humidity levels, it is very comfortable. This is especially true when the radiant temperature from the surrounding surfaces are within 7.2 degrees from each other as they are in a passive house.

Because of the airtight construction, indoor relative humidity is controlled in the winter by the fresh air ventilation system. The design standard seeks to achieve less than 1000 ppm of CO2 and 30% to 40% min. RH in the winter.

Summer humidity levels are often controlled with air conditioning. In areas with mixed climates and higher levels of humidity like here in Philadelphia, a dehumidifier is often required in the shoulder seasons and milder summer rainy days to maintain a comfortable level of RH. This is because AC is needed only a few months out of the year.

The optimal range of RH is 35% to 55%. As with temperature, it is the occupant that ultimately controls the RH.

David Eakin

Kent - agree with all that you have said (I have extended family in Philly and live about 2 hrs West). My point was that there is no design criteria for those things deemed "comfort" (e.g., indoor air temps, indoor RH) but implementing solutions (as you described) will drive up energy use and reduce the apparent energy savings. So you could have a Passive House and still be uncomfortable unless you implement other countermeasures, that may drive energy use past the Passive House requirements. PS - in our area of the MidAtlantic I'm seeing more and more need for dehumidification PRIOR to AC - not just during shoulder months. Been following Matt Risinger's Ultra-Aire/Therma-Stor blog info.