At the 2012 Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Conference in Denver, Dr. Joseph Lstiburek gave the keynote address for the opening plenary (or plenum, as Henry Gifford would say) session. His words, clever as always, added some nice historical perspective to what the Passive House folks are doing but also caught some people off guard.
Read on, and I'll tell you more about that.
First, the history. Joe went way back and started by saying that the igloo built by Eskimos was the first passive house. It uses ice, with an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 2 per inch, but with very thick walls. It has an air-lock entry to minimize infiltration. It has minimal glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.. And, Canuck Joe said, it's Canadian!
Jumping to modern times, Joe discussed the history of energy efficiency and mentioned that that efficiency movement split into two camps back in the '70s: those who pushed for superinsulated houses and the advocates of passive solar, or "mass and glass," as Joe called it. (The passive solar camp has since turned into the renewables camp, with a great emphasis on converting solar energy into electricity with photovoltaics.)
Back in the '70s, though, that camp was focused on capturing the heat from the sun in all kinds of ways. Joe mentioned a few and said, "If you need something like rock-bed heat storage, you've made a mistake."
Why did he say that? "I'm a conservation guy, not a renewables guy." In the end, that's what explains his interest in the Passive House program, I believe.
Following that introduction, Joe launched into the work he did in the early '80s building superinsulated houses. He explained that he was using the Perfect Wall idea first published by N.B. Hutcheon (a Canadian, of course) in 1964. He discussed the R-2000 program in Canada and how it became a boutique program because of unrealistic expectations.
He also showed a lot of photos of his early projects and the failures they had to work through. My favorite was the house where they were going to embed ducts in the slab and then had to fight to get them to stay down as they floated in the wet concrete. That must have been a fun day! It's also one of the reasons that Joe loves scotch so much.
The reason he was doing that work in the early '80s, though, is that he did NOT quit the profession. In 1980, after hitting a low point in his life, he was living in his mother's basement and ready to quit and do something different. Then he went to hear Amory Lovins speak in Toronto and got inspired to redouble his efforts. We're lucky that he did because his work and his company, Building Science Corporation, have helped to blaze the trail for those of us who came afterward.
Joe and his colleague, Professor John Straube, have been critical of the Passivhaus program. In his article, Just Right and Airtight, Joe wrote, "The group that really has me confused are the Passivhaus folks who are pushing 0.6 achACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.@50Pa." In the next paragraph, he wrote:
“Have you any idea how difficult it is to get to 0.6 ach@50 Pa? The number doesn’t seem to be based on anything that makes any sense. It is less than half the R-2000 number [1.5 ach@50 Pa] that didn’t make any sense. What I have been more or less able to figure out is that the 0.6 ach@50 Pa doesn’t come from any energy conservation rationale directly; it seems to be based on the need to prevent moisture problems in highly insulated building enclosures. That is the argument for the number 0.6 ach@50 Pa as I understand it. Never mind that the number, in itself, makes no sense as you can easily design highly insulated building closures without moisture problems that are not anywhere that tight.”
He didn't really raise this issue in his talk, and I think that caught some people off guard. One person told me afterward he was disappointed in the talk because Joe seemed too nice toward the program. He wasn't sure that Joe was sincere. I guess I can see how someone might think that if they know of his previous criticism and then hear the talk, but when I put it all in context, it does make sense.
First, Joe is a conservation guy, and Passivhaus is an extreme conservation program.
Second, Joe invited Katrin Klingenberg to speak at Building Science Summer Camp this year, and he gave an impassioned plea at the end of her talk not to let the Passivhaus program become a boutique program like R-2000 had.
Third, I was hanging out with Joe and Kat the night before his talk (and drinking plenty of scotch), and I can tell you that he really does have a great interest in and affection for the Passivhaus program.
You can find another clue to where he stands on this issue in a comment he made during the annual crawl space Twitterview at Building Science Summer Camp this year.
Asked if Passivhaus is an asinine program, he responded, "No, you just need to keep the good parts of Passivhaus and change the bad parts. And it needs to evolve. A boutique program that impacts a few hundred homes doesn't solve anything."
Joe concluded his talk by saying, "We're family," and he meant it.
I'd like to hear more about where he thinks the Passivhaus standard should go, especially regarding the issue of air leakage, but the substance of his talk didn't surprise me. What did surprise me, however, was that he gave his whole talk without a single F-bomb!
Allison Bailes of Decatur, Georgia, is a RESNET-accredited energy consultant, trainer, and the author of the Energy Vanguard blog.