What follows is a reconstruction of Martin Holladay’s keynote address at the Passive House Northwest conference in Olympia, Washington, on March 18, 2011. The piece has been fleshed out somewhat, in light of the fact that the original time constraints no longer apply. For the most part, each paragraph corresponds to one slide of the accompanying PowerPoint presentation.
Are Passivhaus requirements logical or arbitrary?
Over the last seven years, it’s been exciting to see the Passivhaus standard take root in the U.S., where several dozen Passivhaus buildings have already been built.
But it’s important to remember that superinsulated houses are not new. Canadian and American researchers and builders began building superinsulated homes in the late 1970s.
A brief look at recent history
My own interest in superinsulation can be traced back to my years as editor of Energy Design Update, a superinsulation newsletter launched by Ned Nisson in 1982. I took over as editor in 2002.
In 1985, Ned Nisson and a co-author, Gautam Dutt, published a landmark book, The Superinsulated Home Book.
The book emphasized the importance of careful air sealing measures, and it provided details for building double-stud walls, Larsen-truss walls, and foam-sheathed walls. It described the advantages of low-e glazing, argon-gas-filled glazing, and triple-glazed windows.
By 1985, superinsulation concepts were well understood. Researchers had studied and quantified air leakage in homes. Books and magazines with superinsulation details were widely available. Builders could buy low-e windows, triple-glazed windows, HRVs, and blower doors. Builders had developed a number of techniques for building homes with very low rates of air leakage. And many successful homes with R-40 walls and R-60 ceilings had already been built.
Eleven years after this somewhat arbitrary milestone, Dr. Wolfgang Feist founded the Passivhaus Institut in Darmstadt, Germany, to promote the newly developed Passivhaus standard.
During the 1990s, a group of Vermont builders and energy experts, including Andy Shapiro, were advocating superinsulation techniques. All over the country, builders interested in superinsulation were building similar homes. In the fall of 2001, my photo of one such house — David Hansen’s house in Montpelier — appeared on the cover of the Journal of Light Construction. The house had double-stud walls, an R-60 ceiling, careful air sealing details, triple-glazed Canadian windows, and a Venmar HRV.
Early U.S. reporting on the Passivhaus standard
As far as I can determine, I was the first American journalist to report on the Passivhaus standard.
- In the February 2002 issue of EDU, I reported on a multi-family affordable housing project in LindÃ¥s, Sweden, that was built to meet the Passivhaus standard.
- In February 2004, I published on overview of the Passivhaus standard. The article was titled “Superinsulated Houses in Europe.”
- In May 2004, I published an interview with Katrin Klingenberg and reported on the construction of her home in Urbana, Illinois — a house known as the Smith house.
- In November 2006, I reported on the first certified Passivhaus building in the U.S., a language school in Minnesota known as the Waldsee BioHaus.
- In May 2007, I reported on the Fairview 1 house, an affordable housing project in Urbana, Illinois.
- Finally, in January 2008, I published an interview with Dr. Wolfgang Feist.
Gold stars and a few demerits
What do I like about the Passivhaus standard?
- It is based on the concepts championed by the North American pioneers of superinsulation.
- It sets a high bar for airtightness.
- It requires high-performance windows.
- It addresses thermal bridging.
- It focuses on envelope improvements rather than fancy equipment.
- It sets an energy goal that is in the ballpark of what will be necessary to achieve required carbon reductions.
- PHPP is an extremely useful and accurate design tool.
- The Passivhaus standard is now attracting wide attention, and designers are thinking and talking about design details in a new way.
- The number of Passivhaus buildings is growing.
However, these excellent characteristics of the Passivhaus standard must be balanced against a few flaws and missteps:
- Calling these superinsulated houses “passive” is problematic.
- The claim that these are “houses without heating systems” is false.
- Delivering heat through ventilation ducts makes no sense.
- The annual space heating limit of 15 kWh/m²âˆ™year is arbitrary.
- The PHPP software has no cost-effectiveness feedback.
- The standard has a small house penalty.
- The standard doesn’t distinguish between energy sources.
They aren’t passive
These houses are not passive; they require active space heating systems, active hot water systems, and active ventilation systems. That’s why the original German designation of “Passivhaus” is problematic. For English speakers, the two-word spelling “passive house” is even worse than “Passivhaus,” because it introduces a new confusion — the confusion between passive solar houses and buildings that meet the Passivhaus standard.
The choice of the label for this superinsulation standard (“Passivhaus”) influenced the European decision to market these homes as “homes without a heating system.”
They aren’t “homes without heating systems”
In my early reporting on the Passivhaus standard, I fell hook, line, and sinker for the marketing claim that these were “homes without heating systems.” Based on information provided by Swedish architect Hans Eek, I reported in EDU that the LindÃ¥s development was “the first project in Sweden without any heating systems.”
Later, I had to publish a retraction. In July 2005, I reported, “Total mean electrical energy use per apartment [at the project in LindÃ¥s] was 8,200 kWh per year, including 1,800 kWh per year for space heating …” The heating requirements were very low, raising the question: why exaggerate?
Dr. Wolfgang Feist’s statements on this issue appear to be tailored to his audience. In October 2010, Dr. Feist told a Boston audience, “In the heating climates, a Passivhaus building is not a zero-energy building — you still need to heat it.” In stark contrast, however, the definition of a passive house on the official Passivhaus Institut Web site states, “A passive house is a building in which a comfortable interior climate can be maintained without active heating and cooling systems. The house heats and cools itself, hence ‘passive.’” Yet every single Passivhaus building I have studied and reported on includes an active heating system.
Although some Passivhaus proponents say that no-one ever claims that these are homes without heating systems, the claim is actually plastered all over the Web, in articles posted by writers in Germany, Ireland, Sweden, Denmark, Norway, and the U.S. In fact, all Passivhaus buildings require a heating system. (I suggest that you flip quickly through the slides showing examples of false claims to the contrary; there is no need to read them in depth.)
- A site in Germany has the headline: “Passive House: Houses Without Heating.”
- An article published in Ireland begins, “Imagine moving into a house without a heating system…”
- Another article published in Ireland claims that Tomas O’Leary lives in “Ireland’s first ‘passive’ house — a new home without a heating system…”
- Another article published in Ireland claims that passive houses are inexpensive because they are houses “without a heating system.”
- An article published in Sweden describes a Passivhaus project as “a house without a heating system.”
- Another article published in Sweden, “What is a Passive House?”, says that these buildings are “heated passively by energy from occupants, electrical appliances and sunshine; in short, a building without a heating system.”
- Another article published in Sweden is titled, “Houses Without Heating Systems.”
- An article published in Denmark claims that in a passive house, “there is no need for heat supply or a heating system.”
- An article published in Norway states baldly that “A passive house is defined as a house without a heating system.”
- A PowerPoint presentation from the U.S. is titled, “Passive House: Living Without a Heating System.”
- An article published in the U.S. describes a Passivhaus project in Michigan; the first sentence reads, “Building a home in Michigan without a heating system …”
So clearly, the “homes without a heating system” boast is alive and well. Such exaggerations undermine the credibility of the Passivhaus movement.
Why deliver space heat through ventilation ducts?
The next misstep made by the Passivhaus movement was the declaration that space heat should be delivered through ventilation ducts. It seems that Dr. Feist recommended this method of heat delivery to bolster his claim that these houses don’t require heating systems. In recent years, Dr. Feist has rescinded this requirement, but it still appears in many Passivhaus documents.
This recommendation makes no sense, so it’s worth puzzling out how it came about. The apparent rationale behind the recommendation: since these houses are called “passive,” they can’t have a furnace or a boiler. If heat is added to the ventilation air, it’s disguised, so proponents feel justified in claiming — albeit at the cost of straying from the truth — that these are houses without heating systems.
Why is this heat delivery method such a bad idea? Ventilation airflow requirements are quite low — often only 40 cfm — while the delivery of space heat or cooling generally requires higher air flows. In a cold climate, ventilation air flow limitations and limitations on the maximum temperature of ventilation air make this heat-delivery method impossible.
Some Passivhaus documents make a fetish of requiring that all duct systems deliver 100% outdoor air, and ridicule U.S. forced-air systems that include partial recirculation of indoor air. But there is no scientific basis for preferring 100% outdoor air systems to systems with partial air recirculation. A designer striving to deliver all space heat through ventilation ducts actually has a perverse incentive to overventilate the house, since an increase in the ventilation air flow rate may be the only way to deliver enough heat to keep the occupants comfortable. Clearly, overventilation is undesirable, because it incurs an energy penalty.
Really, who cares how space heat is delivered? The Passivhaus Institut has released contradictory statements on whether the delivery of space heat through ventilation ducts is required; the recommendation is still featured prominently on the Passipedia Web site.
The annual space heating limit is arbitrary
The next problem with the Passivhaus standard is that the annual space heating limit of 15 kWh/m²âˆ™year is arbitrary. The requirement is easy to achieve in a mild climate, but tough to achieve in a cold climate.
Where did this limit come from? It appears to simply represent the space heating energy required to heat a well-built superinsulated home in the climate of Central Europe, with the following assumptions:
- Space heat must be delivered through ventilation ducts.
- Ventilation rate = 0.3 to 0.4 air changes per hour.
- Temperature of ducted air = no higher than 122°F.
- The best windows in Europe are U-0.14 windows; the best achievable air tightness is 0.6 ach50.
With these limits specified, the best houses in a central European climate need 15 kWh per square meter per year for heating. The problem with an arbitrary standard like this is that building a house that complies with the standard may cost much more than can ever be justified by anticipated energy savings.
The Passivhaus software provides no cost-effectiveness feedback
The entire Passivhaus approach provides no cost-effectiveness feedback, so designers often specify very thick layers of insulation — even when energy saved by the insulation is worth so little that the investment makes little sense. These high levels of insulation are specified for a single reason: to meet the arbitrary goal of 15 kWh per square meter per year. North American designers of net-zero energy homes take a different approach than Passivhaus designers: they compare the energy savings attributable to each measure under consideration with the energy production of a PV array. For example, if $1,000 of insulation saves less energy on an annual basis than the energy produced by a $1,000 PV array, then the insulation is not worth installing.
But the PHPP software has no red flag to warn designers that they have chosen to install insulation that costs more than PV, so Passivhaus installers don’t know when to stop making their insulation thicker and thicker. The result: insulation that costs more than a PV array.
When this problem was first explained to me by John Straube, an alarm bell went off in my brain: more expensive than PV? But PV is really expensive — generally $0.28 to $0.75 per kWh. If you are designing a net-zero-energy house, it makes no sense to exceed this level. Since electricity generated by wind turbines already costs much less than the current cost of PV, it’s hard to imagine a future in which energy costs rise to a level that is higher than the current cost of PV. It’s important to note that I’m not advocating that builders actually install a PV array; nor am I particularly interested in arguing over whether insulation usually lasts longer than PV modules. (For the record, it usually does.) I am proposing that the cost of PV is a useful benchmark representing the high limit of likely future energy costs; for this reason, it makes sense to avoid envelope measures that yield a smaller energy return than a PV array. If you add more insulation than this benchmark justifies, you are planning for a future that will never come.
It’s easy to find examples of Passivhaus buildings with very thick layers of sub-slab foam that make no sense from a cost-effectiveness standpoint.
- In 2004, Katrin Klingenberg built the Smith house with 14 inches of sub-slab EPS foam.
- In 2006, the Waldsee BioHaus in Minnesota was built with 16 inches of sub-slab EPS foam.
- In 2007, Rachel Wagner and Michael LeBeau designed a house in Duluth, Minnesota with R-60 sub-slab foam (12 inches of XPS), and the home’s thermal envelope still fell short of the Passivhaus standard.
- In 2011, Ben Southworth built a Passivhaus building in Lancaster, N.H., that required 12 inches of polyiso in the floor — about R-78 — as well as R-148 insulation in the ceiling.
Many engineers have performed calculations to show when the cost of sub-slab foam exceeds the cost of a PV array. According to calculations made by Gary Proskiw and Anik Parekh (published in Solplan Review, January 2011), you don’t need much sub-slab foam, even in Canada.
According to Proskiw and Parekh’s calculations, even in Yellowknife in the Yukon Territory, a basement slab requires no more than R-10 vertical insulation at the slab perimeter. John Straube’s calculations point to somewhat thicker foam, however. Straube says that cold-climate builders should install between R-20 and R-25 foam under a slab on grade. Beyond that point, says Straube, the extra foam costs more than a PV array.
If you see a Hummer parked in someone’s driveway, you might infer that the residents are energy hogs. Is there any more logic to being a “foam hog” — installing what amounts to unnecessary foam — than there is to wasting other types of materials? After all, it makes much more sense to install 2 inches of foam under 7 houses than 14 inches of foam under just one house.
In August 2009, I wrote a blog on this topic, titled “Can Foam Insulation Be Too Thick?” Dr. Wolfgang Feist eventually posted a reply on the GBA Web site. He wrote, “There are those deliberately spreading disinformation. What about spreading such nonsense as ‘PV is more cost efficient’ than slab insulation. Get real guys! … Not nice enough? Offer something better! Contribute to the development. And stop blaming others.”
The Web is full of misstatements about Passivhaus cost-effectiveness. Some examples:
- Dennis Wedlick, the architect who designed New York state’s first passive house, said that the Passivhaus standard is “the most cost-effective way of accomplishing the least energy use.”
- Michael Hindle, a certified PH consultant, said, “Passive House provides the most cost-effective means of achieving the highest goals of LEED’s energy performance criteria.”
- The Web site of Solar Knights Construction in Napa, Calif., includes this misstatement: “Passive House Construction: This standard has become our baseline for building near-zero, net-zero and carbon-neutral structures in a cost-effective manner.”
- Glenn Haupt, a certified PH consultant, wrote the following profile: “Glenn strongly believes that Passive House design coupled with modest scale renewable energy generation is the most cost-effective approach for achieving net zero energy homes and carbon neutral homes today.”
- The Web site of Artisan’s Group, a design/build firm,e claims there is “growing national interest in Passive House as the most cost-effective, sensible solution to net-zero energy housing.”
Unfortunately, however, the Passivhaus standard ignores cost effectiveness. As with the false statements about “homes without heating systems,” these exaggerations about cost-effectiveness undermine the credibility of the Passivhaus movement.
The Passivhaus standard includes a small-house penalty
The next problem with Passivhaus — the small house penalty — is shared by many other standards, including the Energy Star program. It’s easier for large homes to comply with the Passivhaus standard than small homes, so the standard creates a perverse incentive to increase the size of homes. The main reason why it’s easier for larger houses to comply with the standard is that the ratio of the area of the home’s envelope compared to the interior floor area is less for a large home than a small home, so large homes have less heat loss per unit of floor area than small homes. As Marc Rosenbaum has said, “Why should energy budgets be calculated on a per square meter basis instead of a per person basis?”
Not all energy sources are dirty
Finally, the Passivhaus standard doesn’t distinguish between energy sources. If the source of a home’s energy is biomass or a wind turbine, there is less of a need to design a heroic envelope than when the source of a home’s energy is coal. Again, Marc Rosenbaum is worth quoting here: “There is certainly a point where load reduction should hand the baton over to renewable generation.”
Some people in the Passivhaus community have adopted an all-or-nothing posture that stifles legitimate questions. Such a posture raises many warning flags. Beware of false statements and explanations that don’t make any sense:
- Why does the Passivhaus Institut Web site falsely claim that a passive house is “a building in which a comfortable interior climate can be maintained without active heating and cooling systems”?
- Passipedia says that if a building wants to meet the definition of a Passive House, space heat must be delivered through the ventilation system.
- According to Dr. Feist, a Passivhaus building needs to achieve 0.6 ach50 “because you get structural damage without airtightness.”
- According to Dr. Feist, “The reason for the [window U-value] number which we now use in Europe is the comfort of the occupants.”
Conclusions and recommendations
Here’s my advice:
- If the Passivhaus standard can be achieved with insulation that doesn’t cost more than PV, it’s well worth achieving. However, saving BTUs at a higher cost than PV is wasteful of resources.
- We need to start talking about energy use per person, not per square meter.
- Let’s stop calling these buildings “homes without heating systems.”
- Let’s start spelling “Passivhaus” the way it’s spelled in Britain and Germany.
- It’s time to consider climate-specific standards.
Americans can be emboldened by the example of Upper Austria, which (along with 7 other Austrian states) decided to modify the Passivhaus standard to meet local conditions. In Upper Austria, the area of a Passivhaus building is calculated by measuring the outside (gross) area of a building rather than using PHPP’s “treated floor area” method. This difference makes it much easier to meet the Passivhaus standard promulgated in Upper Austria than the standard used elsewhere.
It would be better to change the Passivhaus standard than abandon it.
Read Mike Eliason’s response to Holladay’s address: A Passivhaus Rebuttal: In Defense of the Standard