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Are Passivhaus Requirements Logical or Arbitrary?

Martin Holladay’s keynote address at the Passive House Northwest conference in Olympia, Washington

Posted on Apr 1 2011 by Martin Holladay

What follows is a reconstruction of Martin Holladay’s keynote address at the 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. 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.

Click here to view the presentation slides

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-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. 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., argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -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 Lindås, 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 bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. .
  • 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/m²∙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 Lindås 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 Lindås] 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/m²∙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 energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. 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 PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. 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 XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.), 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 polyisoPolyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. 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 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 zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. 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 StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. 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 biomassOrganic waste that can be converted to usable forms of energy such as heat or electricity, or crops grown specifically for that purpose. 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

Image Credits:

  1. Martin Holladay

Apr 1, 2011 7:56 AM ET

Foam & Carbon
by Jesse Thompson

Great conversation Martin. Two points:

1) Individual designers and builders don't have the ability to decide if they get to spread the available resources for a project across multiple buildings. This is the realm of policy, not design & construction.

If the Energy Apocalypse magically arrives and each community is rationing their last 10 sheets of rigid foam, then we'll talk, but until then it's a distraction to even claim this is a choice of design.

2) In your discussion of the PH space heating limit, you've totally ignored climate damage reduction as a goal of the space heating limit when PHI developed the standard. 15 kWH/m2/yr in a Central European climate turns out to be a reduction of ~80 - 90% in heating energy from typical building stock, which is right in line with all indications of where we need to get to to stop ripping our climate apart. It lines up with Bill McKibben's initiative, and the european Factor 10 and 2,000 Watt Society's goals.

It's not just an engineering game, in other words. We need to get our energy intensity down by really staggering numbers as quickly as we can, and the 15 kWH/m2/yr range lines right up with where we need to be, and was one of the fundamental reasons behind the creation of the specific PH limits.

Jesse Thompson
Kaplan Thompson Architects

Apr 1, 2011 8:41 AM ET

Great article and good
by Armando Cobo

Great article and good synopsis of the Passivhaus program. It shows there are many ways to skin a cat… and no one system is the Holly Grail to achieve high-energy efficiency and healthy homes. As in most cases, exaggerations and misinformation is what brings negativism to green building. Good information and education, helps us overcome the bad rap and hype of most programs in the public view and skeptics in our industry.

Apr 1, 2011 9:11 AM ET

Edited Apr 1, 2011 9:12 AM ET.

Response to Jesse Thompson
by Martin Holladay

1. You're right, of course, that "individual designers and builders don't have the ability to decide if they get to spread the available resources for a project across multiple buildings." But just because "this is the realm of policy, not design & construction," doesn't mean it is irrelevant.

If a design standard results in buildings that are examples of a bad policy, it surely makes sense to consider altering the standard in such a way that better policy results are achieved.

2. I didn't "totally ignore climate damage reduction as a goal of the space heating limit when PHI developed the standard"; in fact, I wrote that the Passivhaus standard "sets an energy goal that is in the ballpark of what will be necessary to achieve required carbon reductions."

Let's look at this issue in greater depth. It is theoretically possible to supply our energy in a carbon-free manner, using a combination of PV arrays, wind turbines, biomass, and tidal power; in fact, the Danish island of Samsø is already close to achieving that goal. The main reason that we haven't already jumped at the chance to supply all our energy in a carbon-free manner (in addition to the fact that the existing energy infrastructure represents a huge investment that our capitalist system is unwilling to abandon or decommission) is that generating carbon-free electricity is very expensive. Dr. Feist agrees with me on this point; he told me, "At the moment, the cost of electricity produced by photovoltaics is in the range of 40 to 50 cents per kWh, which is still ten times the cost of electricity produced by oil or gas. ... I am not against subsidies for renewable energy, but you shouldn’t mix up [the issues] that way. The difference in price is just made by governmental subsidies. You have to be careful with governmental money."

So, we agree that it's theoretically possible to obtain our energy from carbon-neutral sources. We aren't doing it, however, because it's so expensive. So what possible logic is there to addressing global climate change by choosing a solution that is even more expensive than the renewable energy route?

Apr 1, 2011 10:27 AM ET

Edited Apr 1, 2011 6:07 PM ET.

Superinsulation revisited
by Doug McEvers

Passive House has revitalized superinsulation, I have no doubt about it. Superinsulation was the residential building breakthrough and clearly laid the groundwork for Passive House. Since the introduction of PHIUS we now talk matter of factly of R-40 walls and 1 ach50, this is progress.

Apr 1, 2011 12:13 PM ET

Response to Martin, re: subsidies for renewables
by Larry Burks

I'm not an expert so please don't quote me, but I believe the petroleum industry enjoys many subsidies as well. Only a small percentage of the savings is passed onto the shareholders, and likely less onto the rest of us. The gap between renewable and not, is likely to be smaller than it appears on the surface.

Apr 1, 2011 12:16 PM ET

Response to Larry Burks
by Martin Holladay

The statement about PV subsidies was by Wolfgang Feist; I was just quoting him. It was not my intention to knock PV subsidies.

You're quite right that the oil industry (not to mention the nuclear industry) enjoys all kinds of subsidies. I would be in favor of gradually eliminating subsidies to oil companies and the nuclear industry.

Apr 1, 2011 1:27 PM ET

Wonderful summary
by John Straube

Martin, this is an excellent job of summarizing the issues, both good and not so good. This is the kind of discussion we should be having more of.
BTW. The Austrians and Swedes are not the only ones to challenge and modify PH. The French also have a program which started from somewhere other than PH but ended up near the same spot. It is called -- dont laugh -- effinergie, that does a really nice job too. Tweaked what and how is measured, accomodates French climates and building practise, and gets to the same rough range of numbers, eg around 120 kWh/m2 source energy for all energy uses.

Apr 1, 2011 3:04 PM ET

Edited Apr 1, 2011 3:05 PM ET.

I wouldn't agree that we're
by Jesse Thompson

I wouldn't agree that we're not implementing renewables because they're an expensive way to produce energy. We have no problem as a country spending money on areas powerful interests have decided are important (3 concurrent foreign wars?). If we felt like it, I'm sure we could be moving as fast as Germany is in changing our energy mix, but so far we haven't wanted to enough.

It's not because we've been wasting our money on 16" sub-slab insulation :)

In our own practice, we're trying to keep our eye on the primary reasons we're working on these problems beyond merely enjoying the technical challenge, and in my opinion the climate destruction issues are first and foremost. You mentioned it as one bullet point in a long list, but whenever I've been around PH advocates, climate change mitigation is the first reason mentioned for the standard's existence.

Technically, I agree with you, in our colder northern climate we've generally seen that the PV production cost tipping point arrives before a building meets PH, but that's also because we haven't been as skillful (or have been too constrained by our renovation projects or urban sites) at being good passive solar designers to take advantage of all the free heat we have in our climate.

Our current wave of buildings is doing much better at this now that we're using PHPP for analysis and can really see how every individual window is working as a little heater (or not).

Apr 1, 2011 6:55 PM ET

cost issues
by samuel koerber

You have to accept basic economics as a fundamental rule of reality or your efforts will have no far reaching impacts. The challenge is to get people to understand the true costs of the choices we make once we factor in the life expectancy of the building and the environmental costs of the energy source we are using. Ignoring economics simply means that you have the luxury to ignore economics because you are one of the elite. Which for most of us in the US, we are, whether we feel it or not. Global climate change will not be stymied by a standard that ignores cost effectiveness, it will merely be a cool niche market and maybe an example to future post apocalyptic societies. If you have money to spare and climate change is your main concern, why not spend the extra money on a massive pv installation and stop at 4" of sub slab foam. Governments don't always make very rational economic decisions (three foreign wars) but private markets generally do, of course when private markets are injected with government backing of insurance for nuclear power than the whole thing gets skewed. I think we we should build the houses that make sense to build based on the cost of wind and solar like Martin says and work to see a change in government policies that allow the true cost of our choices to be more obvious.

Apr 2, 2011 5:58 AM ET

Second response to Jesse Thompson
by Martin Holladay

While I agree that adding unnecessary insulation under the slabs of our buildings is not the reason that our nation lacks a commitment to renewable energy, I fail to understand your apparent disregard of the economic discussion I have raised.

If a mix of renewable energy sources can provide energy without negative effects on our planet's climate, and if that solution is cheaper than adding 14 inches of foam under our homes, how is this economic discussion irrelevant? It appears to go right to the heart of the matter. Architects who choose the thick-insulation route are choosing an expensive path, and doing a disservice to their clients.

Apr 2, 2011 12:25 PM ET

Edited Apr 2, 2011 12:26 PM ET.

by Matthew Amann

I suggest that you all realize that you will not change each others' minds, that is if you are as sure about your views as I am of mine. We are all on the cutting edge of the learning the best building technologies, implementing what we think is right and what we can afford. While I think Martin's picture pretty much sums up the issue, I don't think Passivhaus is truly, at this time, about moderacy for the masses, it's more about, please read with a sense of humor,"We're German energy Nazis, look what we have done". And I understand it, but 14" of foam is not even responsible, unless you're trying to heat your home with farts in Siberia.......

Apr 2, 2011 1:35 PM ET

A voice of reason
by bill bradbury

As a BPI certified contractor specializing in deep energy retrofits of historic homes, I am caught in the middle of; clients, architects, inspectors, sub-contractors and government and utility rebate programs. Each of these people has his or her own agenda and have gleaned enough disinformation to formulate an opinion that supports that agenda, so when I read an article like this, balanced and thoughtful, it makes me so happy that I have to post. We ( yes us, the ones with the computers, who have done this to the world) are stuck in quicksand. If we do nothing, we will go under, but if we flail around without direction, we will go even quicker. We need to work together to build a rope, not argue about what kind of rope is best. Instead of supporting your point of view to the end, humbly weave yourself into your own community. Be the rope you want to see.

Apr 2, 2011 5:01 PM ET

Passive House as Rule of Thumb gone awry
by Brennan Less

Martin, great article! I dug into comparing net-zero energy design approaches (BEopt for example) against the Passive House design approach a couple years ago, and I came to nearly the same conclusion as you. I think the PH standard was developed as a set of "rules of thumb" that would lead to near-optimal cost-effectiveness, IF the conventional heating system was done away with. Cost-savings/effectiveness though elimination of the conventional system is the crux of the argument, and was the driver behind development of the standard, in the context of Central Europe. But as we know, rules of thumb are often less useful outside of the context in which they were developed, and they are a method that is supposed to simplify analysis. Carefully conceived rules of thumb should get you near optimal solutions without the help of overly complicated technical analysis, and PHPP does not give this. I think the rule of thumb that is the PH standard is out of context in much of the US, and as a result, we get perversely designed buildings with 16" of sub-slab foam. The goal in PH design has become the religion of the PH standard, WITH the best of intentions, of course.

Apr 2, 2011 8:14 PM ET

passivhaus as rule of thumb
by mike eliason

would be correct if PHPP wasn't so accurate and proven across a wide range of HDDs.
within the context of central europe, it's more difficult to achieve passivhaus than in the US.

the 16" sub slab foam is the anomaly based on several factors, none of which include passivhaus being used 'out of context' - especially as that context is built upon north american pioneers.

Apr 2, 2011 8:18 PM ET

Meaning what? Mike Eliason
by Matthew Amann

"within the context of central europe, it's more difficult to achieve passivhaus than in the US." Explain your point further if you would sir....I certainly don't see any vague "rules of thumb" I see German detail fixation, which quite honestly I am a victim of......

Apr 2, 2011 11:30 PM ET

Edited Apr 2, 2011 11:53 PM ET.

I am all in with what Bill
by aj builder, Upstate NY Zone 6a

I am all in with what Bill Bradbury posted sort of.... The discussion is great, but the actual building of all kinds of low energy, no energy, carbon neutral, non polluting healthy fun livable homes is... super-active-passive-cali-fragile-istic-extra-all-n-ala-doshiaus!

I gots lots of rope and am even pretty darn good at a weave splice of sorts....

Here's my nickel's worth...

Let's rebuild a 100,000 homes to net zero this year and then do 10% more each year following. Rules? Any damn way you feel you can get there. With or without LEED, PH, EnergyStar, and all the rest. Foam, no foam, some foam. Do it your way and in groups and individually. Be a do-er. Be a proud rebuilder of a home to Net Zero!

The 100,

Off to ready me rope for some weave splicin...

Apr 3, 2011 12:24 AM ET

ease of achieving PH
by mike eliason


When I take a project in PHPP and migrate to every climate in the program, tracking resulting specific heat demand, the EU climates are trending higher (meaning more difficult) than North American ones. I've done this to several projects, and the results are all similar to the graph posted yesterday (

So to say that the envelopes here are perverse, when most EU envelopes aren't as perverse and it's harder to achieve PH there - tells me that there is a disconnect. The rules of thumb are there, but it's possible they've been ignored. They relate to orientation, massing, etc.

We need better rules of thumb in designing a passivhaus. The technical analysis will get you the rest of the way. Frankly, I've never found the analysis part to be difficult or complicated, and we use it as an integral part of the design process, constantly refining so we can avoid those perverse assemblies.

How are you a victim of details?

Apr 3, 2011 4:48 AM ET

Edited Apr 3, 2011 9:10 AM ET.

Response to Mike Eliason
by Martin Holladay

You write, "the 16-inch sub slab foam is the anomaly." But observers in northern climates are seeing R-50+ sub-slab foam and R-90+ attic insulation in PH project after PH project, from very smart designers who can't easily be dismissed as idiots or misguided fools.

So it's not enough to tell those of us in New England and Minnesota, "Just sharpen your pencil. There must be a better way to do it." Because these smart PH consultants tell me, "I keep going back to the spreadsheet and I can't hit the number without R-50 under the slab and R-100 in the ceiling."

So, if these very smart designers can't do it, and Mike says, "Well, they should be able to do it with a lot less foam," then there's something about the software that makes it particularly hard to use. Because these designers in New England and Minnesota aren't idiots.

And if the software is that hard to use -- and if the software even confused Katrin Klingenberg, who after all built a simple cube without any bump-outs -- then I think it's the Passivhaus standard that needs to sharpen its pencil, not cold-climate designers.

Apr 3, 2011 8:01 AM ET

by John Brooks

Mike Eliason,
I admit that I have not designed any extremely high performance homes to date.
I have only designed a few "Half-Assive' homes (Homes with A HERS Index around 50)

Can you provide links to some of the Passivhaus Homes that you have designed and Built?

Apr 3, 2011 9:16 AM ET

Response to John Brooks
by Martin Holladay

Do your homes fully comply with all requirements of the HalfassivHaus standard?

Apr 3, 2011 11:28 AM ET

built Passivhaeuser
by mike eliason


re: PH homes - none built yet, but we're working on it.

I can point to two certified Passivhaus projects in 8000 HDD+ North America climates that don't have R-100 assemblies or 16" sub-slab insulation.

1. Osterreichhaus, Whistler BC:
ground: R-47
wall: R-47
roof: R-54

1. Bagley Nature Center, Duluth MN:
ground: R-53
wall: R-64
roof: R-85

The Bagley Center, based on our research, could have lowered their insulation levels with better glass. In our findings, the Cardinal 179 is decent glass, and is still energy positive in this project, but routinely comes up short compared to EU glass.


The R-50slab /R-80 roof is the upper limit we're seeing for projects we've migrated around North America. But that's not 16" in the ground, and it's only in the more extreme portions of the Midwest and New England. Most of the East Coast needs less.

For maximizing solar gain (or daylight, or natural ventilation), a cube isn't the most efficient shape. I know these consultants aren't idiots - in fact most are a hell of a lot smarter than we are. But maybe the biggest problem is going back to the spreadsheet - but not going back to the drawing board. Dr. Feist's Kranichstein project is a great formal model - compact shape oriented east-west with no bumpouts, simple roof line, maximizing glazing to the south...

Honestly, when you start there - the numbers start to look less dramatic than when you start by shoehorning a design into a Cape Cod or Saltbox. Perhaps this means Passivhaus and modern architecture are better paired?

Apr 3, 2011 12:27 PM ET

Edited Apr 3, 2011 12:29 PM ET.

by Matthew Amann

Mike, the victim comment refers to my fixation on details. I don't view the Passivhaus standards as ambiguous "rules of thumb", but as fairly acute prescriptions. Rules of thumb would be superinsulate, passive gain, grid tied solar, solar hot water, energy efficiency, massing, etc; this is how I build homes. Although my homes are efficient and well detailed, I am sure I don't meet the Passivhaus standard, and believe doing so is actually arbitrary in itself. As with LEED, I believe it is divisive, saying THIS is good, and THAT is not, meaning the way the rest of us are building. Not to say I don't believe in the core elements of Passivhaus and LEED, as I try to implement building styles that appease both. As far as the Cardinal 179 glass, triple pane American wood window with the low-e on the #3 surface, I believe it gets close to the performance of the uber fiberglass and uber German wood windows' performance, at roughly HALF the cost(of the serious windows anyway).

Apr 3, 2011 2:14 PM ET

Edited Apr 3, 2011 2:14 PM ET.

Don't get too wound up... It's still early.
by albert rooks

Obviously it's a little early to say that there is a last word on how much underslab foam is needed for an American PH Project in a northern climate. It would be naive to think there is enough data to support a statement that the Passivhaus requires 16" of foam in high HDD climates.

A little more patience and time is needed before a "rush to judgment".

As Martin admitted (and thereby aging himself -smile) He was involved in super insulation in the US at it's inception. I'm sure that he would not say that they "had it down" to an optimized approach in a few years. There were only a few working in the field and you can only learn so fast...

The PHPP is the crux of the underslab foam issue. Getting a project through it is demanding. The PHPP is a tool created in Germany. When it's used (today) in Germany, the values used are based on products and values that are available in that market... And at market competitive prices due to concentrations of vendors in competition with each other.

Currently, the American designer does not have that luxury. And in this case -it is a luxury. The American Designer is having to: 1, Learn an extremely complicated new tool designed in a non english speaking country. Work with materials that are not native to the tool, trying to "shoe horn" North American products that don't have the high values common to the practice. And then deal with building shape orientation options that for the most part, have not even made it on the radar... as even a variable that one would adjust.

Considering the handicaps in being an early PH designer/builder in the US, is it any wonder that underslab foam is one of the first "go to" points for getting it through PHPP? It's far less expensive than Import windows and doors with the values needed.

And what does that mean? That PH is too foam reliant -or- that our supply industry is behind the supply industry of Europe? We don't have the product choices here... And we have to work with what we can economically get.

Too say that the only PH option is for far too much foam is, at this point, is a rush to judgement.

I mean come on... We're just getting warmed up!

(No pun intended.)

Apr 3, 2011 3:15 PM ET

Edited Apr 3, 2011 3:21 PM ET.

Mike Eliason's R-values
by Martin Holladay

Your examples of R-50 floors prove my point. An R-50 floor, according to John Straube's calculations, requires between twice as much and 2.5 times as much sub-slab foam as can be justified by comparing the energy savings of the foam with the energy output of a PV array.

Apr 3, 2011 6:33 PM ET

R Values continued
by albert rooks


Now that the examples are out of the range of your sketch (thank goodness it was not to scale! What was that: R-150 compared to R-2?) and into the R 50 range, I've lost the thread of the issue:

MH: "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 seems to me suggesting that: in Mike's above cases, R-25 foam is better than R-50 foam is semantical. If either measure is equalizing the same demand, does the issue then turn to a suggestion that PV is a better strategy than sub slab foam?

I can see the case for R-70 and up. I make no secret of the fact that I'm not a big fan of foam, but if there is foam going under the slab, than going from R-25 to R-50 seems to me to be in a reasonable range, and not what I would consider a "foam hog".

If I have it right that your advocating the same load reduction is better delivered by PV than foam (in this R-25 load range), then I feel it is important to bring up the points that you were not interested in discussing:

MH: "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.) "

Those above points are important to the "lasting effect" of load reduction. It eliminates the issues of owner care, lack of owner care, and the failure of the PV array to remain in place due to remodel, re-roofing, storm damage and other cases that can cause the PV to not deliver the load reduction. The point after all is- that a load reduction actually happens.

It's not just a semantical cost argument: PV is better than foam -or- foam is better than PV. Durable and Passiv envelope improvements should always trump roof top gadgets.

If buildings can be built in this range, with durable results, then I don't see how 15kwh/m2 is arbitrary. There is nothing wrong with an R-50 slab.

Why settle for mediocre results as a benchmark? I'm hoping that getting the envelope load down to PH levels is the starting point. Project budget or not, there are those (certainly myself) who see this load reduction as a way to leap frog over zero and head to plus homes. It'll be a disappointment if we get there and you've already filled the roof with PV to get to zero just to make up for poor windows and slab demand.

Apr 3, 2011 6:51 PM ET

Edited Apr 4, 2011 1:06 AM ET.

Straub's calcs
by mike eliason


I don't know what kind of project John ran through PHPP to determine those calcs, so it's hard to get around his thinking on them.

Here is what I do know. I put together a compact 1440 gsf (TFA=1236), 3 BR project. I migrate that to Minneapolis (8033 HDD), and have to add a little insulation...
Walls: R-44
Slab: R-34 (4" slab on grad over 7" type IX EPS @ R-4.55/inch)
Ceiling: R-57
Windows: R-6.5 (installed)

The resulting PHPP specific space heat demand comes in at 4.67kBTU/ft2a

If I peel the ground slab back to the BSC R-10 approach (walls and roof are already at BSC levels), the specific space heat demand jumps to 7.47kBTU/ft2a.

this is a difference of 2.8kBTU/ft2a. I then go to the PE Value tab, and can find out how much PV is needed to make up that difference: PHPP says just over 1,000kWh/yr.

1. Is 292 (700 sf * 5") cubic feet of EPS, plus scraping a little more dirt for the slab really more cost than enough PV to produce 1000kWh/yr, which in Minneapolis appears to be about a 0.6kW system?

2. With the additional 5" of EPS in my Passivhaus, it's a one-time 3,205 CO2 output. PHPP shows the CO2 emissions of the PV at 0.41lbsCO2/ft2-yr, which equates to 507 lbs CO2/yr total. Over 30 years, that PV is responsible for 15,210lbs of CO2. Is the active approach, which emits another 6 tons of CO2 before taking into account the embodied energy of the PV panel the right approach?

To me, it's a no-brainer, especially if we're talking about reducing energy bills AND CO2 emissions - that tuning the envelope correctly (which may mean thicker slab assemblies than we're used to) is the way to go.

[edited to reflect correct TFA]

Apr 3, 2011 7:36 PM ET

i'm between Martin and Mike
by j chesnut

I haven't read this whole discussion carefully but here are a couple points to add -

I don't know who Martin has been speaking with in Minnesota but I think the R values Martin points to (R-50 slab, R-100 roof) are elevated based on my experience with the PHPP in the same climate. Even though smart people are working on this stuff there is too much going on to nail it down in the first two designs even. Martin give us some time to get to our third project and beyond and get some feedback from how the projects act in the field. Passivhaus is still maturing in my area and part of the elevated cost is the fact that it is new.

Mike, I would caution anyone trying to achieve Passivhaus, in a cold climate at least, to not try to widdle down insulation levels by maxing out solar heat gains. The day/ night temperature fluctuations need to be considered as well as periods of no clear weather. Balance between high levels of heat retention and allowing only as much solar heat gains in the winter as needed is key (you can have an excess of heat gains even during the coldest Minnesota weather). Light construction lacks the thermal mass of construction more common in Europe so watch out for increased day/ night temp fluctuations.

My opinion still stands that learning Passivhaus is the best method for any cold climate designer serious about making an energy efficient buildings. The fact a designer needs time and experience to fully understand the software isn't a bad thing.

As for cost optimizing software, what designer wouldn't love to have cost optimizing software!

Apr 4, 2011 4:20 AM ET

Edited Apr 4, 2011 5:42 AM ET.

Response to Albert Rooks
by Martin Holladay

It seems to me that much of the desire to hit the Passivhaus number is emotional rather than logical. The argument seems to be, "R-50 instead of R-25 isn't that much more -- why are you making such a big deal about it? After all, that's what I need to get the certification, so it's worth it."

I feel that basic math and economics aren't enough to convince Passivhaus die-hards, so perhaps it's not worth trying. After all, it's a voluntary program, and if you want R-50 foam under your slab, go ahead.

I'll make one last stab at introducing logic, however:

1. To set up a basis for understanding PV costs, I'll quote Dr. Wolfgang Feist, who is respected by the Passivhaus community: "At the moment, the cost of electricity produced by photovoltaics is in the range of 40 to 50 cents per kWh, which is still ten times the cost of electricity produced by oil or gas."

2. If someone is building a net-zero-energy house, they have to assume that their energy costs are equal to the current cost of PV. That's expensive electricity, but some people want a net-zero-energy house anyway.

3. According to Dr. Straube's calculation, if you are building a cold-climate net-zero-energy house, you should put R-20 or R-25 foam under your slab. After that, the foam costs more than PV. Almost no one puts R-20 or R-25 foam under their slab, though, because it's really expensive to build a net-zero-energy house.

5. Passivhaus proponents are proposing R-50 foam under a cold-climate slab -- twice as much as is needed for a net-zero-energy house. They aren't just assuming that the cost of electricity will rise to 45 cents a kWh like people who build a net-zero-energy house. They are assuming, bizarrely, that electricity will cost much, much more than the current cost of PV. When? I don't know.

6. So, net-zero requires R-25. It's wicked expensive, so it's rarely done. Passivhaus says, "Install twice as much as is needed for a net-zero-energy home." Well, you can do it if you want the PH certification -- so go ahead. But the math doesn't make any sense.

Apr 4, 2011 4:42 AM ET

Response to J Chesnut
by Martin Holladay

I think you made an important point about south glazing area when you wrote, "I would caution anyone trying to achieve Passivhaus, in a cold climate at least, to not try to whittle down insulation levels by maxing out solar heat gains. The day/ night temperature fluctuations need to be considered as well as periods of no clear weather. Balance between high levels of heat retention and allowing only as much solar heat gains in the winter as needed is key (you can have an excess of heat gains even during the coldest Minnesota weather)."

I've seen two or three Passivhaus designs that make me nervous -- big walls of south-facing glass, obviously driven by the numbers on the PHPP spreadsheet. More solar gain appears to make the spreadsheet work, but at the risk of overheating during sunny weather in March and April, and at the risk of poor performance during long cloudy stretches of weather in November and December.

Apr 4, 2011 5:35 AM ET

Edited Apr 4, 2011 5:38 AM ET.

Response to Mike Eliason
by Martin Holladay

You wrote: "I don't know what kind of project John ran through PHPP to determine those calcs, so it's hard to get around his thinking on them." If you want more information on John Straube's calcs, see the extensive explanations in my earlier blog, Can Foam Insulation Be Too Thick? and in the comments to that blog.

Here are some of Straube's assumptions:

— “A slab on grade insulated to R-32 in Finland had an average heating season soil temperature of 12.5°C (55°F). Hence, during the heating seasons the average temperature difference between soil and indoor air is about 15°F.”

— “If you account for a coefficient of performance of 2.5 for the heat pump over the season (3.3 in 40°F weather but 2 in -10°F weather), the cost of PV-powered heat is no more than 60/2.5 = 24 cents per kWh. Note that many central forms of renewable electricity production work at 25 cents per kWh, such as wind, microhydro, tidal, biomass, concentrating solar thermal, etc. So this seems like the high end of electric production costs.”

— “The cost of insulation becomes more than the cost of generating energy for the walls in a typical house in a 7,200-HDD climate at about R-60 (using the Building Science Corporation approach), and slabs [on grade] at about R-20 to R-25, depending the cost of placing EPS (which costs around 10 cents per R per square foot).”

— “If I base my design on real measured results, rather than someone's model, I repeatedly find that the temperatures of the sub slab range from the 10°C to 15°C range (50° to 60°F).”

— "By measuring the soil temperature under a slab, the impact of insulation on reducing heat flow and the insulation and thermal storage capacity of the soil are directly considered. No estimates or fudge factors needed. All but the Cardiff slab were measured in a cold climates with lots of insulation (4 to 8 inches), so the impact of heat loss should be mostly accounted for. Heat flow through a layer of insulation, whether under slab, roof, or wall, is driven by the temperature difference across it. For roofs, the challenge is to account for the solar impact on the surface temperature. For slabs, the challenge is to estimate the soil temperature. So, I repeat, regardless of the fudge factors, standards, estimates, and computer models, heat flow across an insulated slab is due to the temperature difference across it, and the limited measured data provides consistent information about the size of this temperature difference. The real-world measurements simply do not match the standard approaches and assumptions.”

— “I use an average of thousands of measurements (hourly) over the year. As you must know, the thermal mass of the soil under the slab means that the temperature varies incredibly slowly. I did not use a steady state model. I am using measured boundary conditions that are far from steady state. I have also done these types of calculations with Heat 2D, a dynamic 2D program, and was brought up on Mitalas's brilliant and still relevant basement heat loss models, which include 3D effects, dynamics, etc but unlike all other models, was carefully benchmarked against multi-year heat loss studies of DOZENS of REAL basements (the reason I trust his results more than most other paper studies).”

— “Of course the perimeter is different than the edges. Of course geometry has an impact. But both of these do not affect the answer to the basic question of how much insulation should be under a slab. I hope it is also obvious that the perimeter should have more insulation if it is easy to do so, and the center less. My calculations are normally based on a 7.5x12 m floor plan, which … reflects the lower 50% of the housing market in North America, and probably 70% in Europe. A 10x15 plan is OK for a ranch house, and will mean the perimeter zone is about 25% of the total slab area, depending on your definition of a zone. Physics of heat flow across a slab much wider than it is thick exposed to slowly varying temperatures: Q = U A Delta T. The only issue is the Delta T.”

Apr 4, 2011 9:25 PM ET

Question for Mike Eliason
by Matt Jennings

In 2nd through 4th sentences after the number 2 in your comment, do you say that PV panels EMIT CO2?

If I am reading your comment correctly, could you explain how a PV panel emits CO2 during use (ie separate from the emissions created to manufacture the panel)?


Apr 4, 2011 9:48 PM ET

Passive solar
by Chris Herman

I really appreciated Martin's recognition of the confusion caused by using passive house vs. Passivhaus. I have been designing passive solar homes in WA state for 24 years and feel like my specialty label has been co-opted. I'm sure this causes some folks to make assumptions about my design strategies because they have heard of Passivhaus, and those strategies seem extreme for our mild climate. I have worked very hard teaching classes, giving talks, writing articles and developing a criteria for cost effective passive solar homes in WA state. I feel like I have been hit with a double blow when Passivhaus proponents' considerable marketing confuses my potential clients into associating me with them and then further hurts me by using all my good work to get audience for their techniques. I am familiar with double wall construction and super insulation from my education in the early 80's. They were called envelope houses and didn't make much sense in western WA's mild climate. Even with higher energy prices 30 years later, I'm still not convinced that taking up more floor space and using more resources to achieve super duper energy efficiency is worth the trouble and expense, especially with a limited budget. I have attended a few introductions to Passivhaus standards and have always specified above code insulation and windows. Since air leaks are typically the biggest heat loss area I am very diligent with air sealing details. As a Lung Assoc. certified healthy house designer, I am also concerned about making houses super tight when so many finishes and furnishings available in the U.S. are made with petrochemicals. Hi tech ventilation systems are only as good as their installers and operators. I appreciate designers pushing the envelope of energy efficient design. I wish the Passivhaus folks would get their own term for it, like high performance or super efficient. Because as you said, these phpp houses are not passive.

Apr 5, 2011 12:37 AM ET

CO2 output of PV
by mike eliason


PHPP doesn't consider grid-tied PV as carbon neutral, but carbon reducing. the house still draws energy from the grid at night and during winter, and while you can net meter a house - you aren't zeroing out the CO2 emissions from grid-utilized source and transmission losses. As such, there is an associated emissions factor, and PHPP kicks out the resulting CO2/ft2a.

Apr 5, 2011 1:15 AM ET

Great Article, BUT
by Kevin Dickson, MSME

The real congratulations goes to the brave Passivhaus folks who invited Martin to speak. They must have known they would get a healthy dose of real science aimed squarely at their sacred cows.

Apr 5, 2011 3:21 AM ET

The cows and their tenders in the field are doing just fine
by albert rooks


I do get your point about a cost valuing insulation levels in the PHPP as being an improvement. It's a good point and would be a good feature. No doubt. I am not "die hard" to the point that I would not respect your opinion on this or any other issues. I come to GBA to get it so don't hold back.

Frankly it's great that we have the opportunity to push these issues around. I certainly hope I don't come off as "it's Passivehaus or nothing". The reason most of us are in "low energy building" is to get more good buildings built. Regardless of how much sub slab foam, or what "program" they are built in.

So thanks for the opportunity and the "gentle nudge" to examine what we're doing and why.

I hope I can be forgiven, and still be viewed as "sane" if I have a "favorite path". Obviously I can't answer the issue of how Dr Feist chose 15kwhrs/m2. I think that I, along with many more, understand why that mark was chosen. I've gone to both US and european conferences and heard the presentations and they match: It's a reachable level of load reduction through passive envelope improvements and orientation. That's not to say it's an easy one. Nor is it to say it's for every project.

I also want to acknowledge all of the positive things that both you, and Dr Staube, have said in this post about what the introduction of Passivhaus has brought to the US. MH:"The Passivhaus standard is now attracting wide attention, and designers are thinking and talking about design details in a new way." Hopefully that continues and doesn't stifle other developments, values or viewpoints.

It would be presumptuous of me to speak for PHUIS or PHI, but I can say that the hopes of Passive House Northwest are that PH in our region adds to the overall atmosphere of low energy building to both it's practitioners and the general public. Regardless of what our personal favorite is, regionally we support every form of energy efficient building.

With that, I'm going to let the subslab foam issue drop. I really don't think it's important today to have a final word on what is possible with the PHPP as it stands now. Both you, me and J cheastnut have admitted here that there are really not enough projects on the ground to see what American designers can do with it. Even Dr Staube pointed out that the PH standard was "tweaked" in France, but wound up near the same values. It means to me that it's attainable and bears further investigation before applying the label "arbitrary".

Ps... I love the "HalfAssiveHaus". We'll need to develop the HalfAssive Planning Package. (HAPP).



Apr 5, 2011 11:02 AM ET

thoughts on conservation vs production
by Dan Whitmore

I guess I'm going to join in here and though I may be on the 'illogical'' and non-scientific standpoint, my experience comes from being in the building trades for 25 years, living through the ‘70s & ‘80’s in a well-monitored & well-engineered (for the time) Solar Home (passive and active), and also being a numbers geek.

The main point of contention I see flowing through the conversation is the idea of the most cost effective method of meeting the energy needs of a building's occupants in an environmentally conscious method. In our reach for this I really don't think we can set aside the soft sciences, namely human behavior. This is why a passive approach holds the most promise in my view.

Utilizing active systems demands higher levels of human involvement. Call me cynical but my hope for humanity-in-general's motivation to maintain an optimized PV system is rather low. Maintaining a substantial thermal envelope is generally no different than non-super-insulated structures.

As for the high–cost of the thick blanket in a Passive House approach, cost effectiveness in any project always rests with the designers and builders. As folks have said above, sharp pencils, experience and optimal use of available materials are the main means there. As for conservation vs production (foam vs PV), one of my main concerns is how an alternate method will affect the building production. We can’t just look at material costs isolated from installation. The Passive House I’m finally completing does have thick layer under the slab field. Placing 4” under the perimeter grade beam took no less time than the center 11” (ok maybe 1 hour less). Is this overkill in a 4900 HDD climate? Possibly. However, having the higher inner portion also allowed me to reduce the need for fill. Spending a good amount of time crunching a numbers and using PHPP as a tool enabled me to create a very cost effective sub-slab assembly sequence. And the extra few inches? They helped allow the use of a less expensive and local window package.

Our pool of successful Passive House projects is still rather small. Examples are being added regularly, currently I’m bidding a PH Single Family House that uses just 5” of sub-slab foam. One of the beauties of PHPP is it does allow the designer to readily adjust placement, material and thickness of the blanket.

Don’t get me wrong, I am a fan of a PV, co-generation, wind +++. However I think they are best utilized in concentrated situations. The cost effectiveness of a significant installation on a nearby institutional/industrial or such structure would be soooo much more cost effective (from both installation and maintenance standpoints) than on a single family house.

Yes I’ll agree the 15 kWh/m²∙year is set somewhat arbitrarily. Some think it should be more stringent, especially for our climate here in Seattle. Is that illogical? Less logical than concentrating populations in climates with 7,000 or more heating degree days and deciding that supplying the energy to keep comfortable (at the flick of a switch) is more important than political and environmental instability?

As for how the Solar Home from 30 years ago doing? It’s still there and reportedly warm/cool, but all the active Solar elements have now been stripped (and not replaced) while the passive ones continue.

Apr 5, 2011 11:12 AM ET

Response to Dan Whitmore
by Martin Holladay

You've raised many good points. I couldn't agree more with your point about passive systems outlasting active systems; the researchers who built the Saskatchewan Conservation House in 1977 came to the same conclusion, and there are lots of examples of passive solar homes from the 1980s that still work well but have abandoned one or more active elements.

I think you misunderstood my point about the cost of electricity generated by PV arrays. This is what I wrote: "I'm not advocating that builders actually install a PV array; ... I am proposing that the cost of PV is a useful benchmark representing the high limit of likely future energy costs."

Most homeowners want to leave the hassles of electricity generation in the hands of their local utility, and that's as it should be. In the future, as now, almost all Americans are likely to get their electricity from their local utility -- they won't be generating electricity on site.

At the risk of repeating myself, I'll try to explain why I think the cost of generating electricity from a PV array is a useful benchmark: (1) It's a technology that already exists, and (2) It's expensive -- more expensive than several other types of renewable energy, notably utility-scale wind.

So that if our utilities make a total switch to renewable energy -- a mix of wind, tidal power, PV, and biomass, with a little bit of deep-hot-rock thermal generation thrown in -- it will never cost more than the current cost of PV-generated electricity.

Apr 5, 2011 4:48 PM ET

Edited Dec 30, 2011 10:32 AM ET.

Another rebuttal - this one from Graham Wright
by Martin Holladay

You can read Graham Wright's rebuttal of my keynote speech here:
Response to Martin Holladay's critique of the Passive House movement.

Apr 5, 2011 5:36 PM ET

Edited Apr 5, 2011 5:39 PM ET.

swiss standard
by marc ritter

interesting observations about the standard. you might also want to look into the swiss standard of passivhaus, which has a much better name: minergie [minimal + energie (energy)]

btw, if you take a look at old (and yes, 100+ years) houses in the alps, you would find them to be quite possibly the first energy efficient homes, with stone walls 3+ feet thick, "powered" by wood burning stoves.

Apr 5, 2011 7:04 PM ET

by mike eliason

minergie isn't equal to passivhaus, though they do have more stringent levels of certification, including one based on passivhaus (minergie-p) and a 'green' label, minergie-eco. both can be combined for a super green high performance building (minergie-p eco)

minergie goes off ERA (energy reference area) which is gross floor area, instead of the more stringent treated floor area (TFA) of passivhaus (basically livable area from gyp-gyp minus a fraction of storage/mech, stairs, etc)

there are a number of other subtle differences as well, different source factors, performance criteria, etc.

Apr 5, 2011 11:31 PM ET

Losing the forest for the trees
by Katy Hollbacher

I have really appreciated GBA, John Straube etc.'s critiques of Passive House... this is what evolution is all about, continually questioning & rethinking & improving. These discussions are invaluable, not to mention entertaining (I was sad to miss the fun up at PHNW!) I've been perplexed & a little frustrated by some Passive House evangelists that are so defensive, seem unwilling to accept the notion there could be potential improvements to be made w/ PH... it's the Holy Grail, can do no wrong, is perfect and will save the world all by itself. Don't get me wrong, this is a wonderful standard and I'm a huge proponent--but of course it's not perfect. And while this work we're doing is very important, it's still just a small piece of what this world needs. How will our world look with automobile-dependent suburbia filled with Passive Houses? Or an Afghanistan where every building is a Passive House but a woman better not flee from her abusive husband lest her nose and ears get cut off?

Back to the point, these are my main observations:
1) People can and do get caught up in the numbers and sometimes end up missing the point and doing REALLY illogical (and certainly not cost-effective, no matter how you slice it) things with their projects. But I don't see this as such a terrible thing--rather part of the evolution of high-performance building in this country. It's too bad when a "bad" example is overly harped on, potentially misrepresenting the standard on the whole, giving the public the wrong idea of what it takes to get to PH. But I think this comes with the territory of learning and applying what is, in this country, a new standard. Bring on the critiques--everyone needs to hear and learn from them.

A challenge I've seen is that we in the U.S. lack experience with the standard, and tools, those in Central Europe have had for 10+ years. As Martin said, many smart people are building PHPP models. But--these smart people haven't necessarily been taught all the aspects of the PHPP, or might not understand the importance/sensitivity of certain data that can hugely (and positively) impact the numbers. We don't yet have the luxury of a comprehensive book of details from which to pull thermal bridging coefficients, so certain details that might be beneficial to a project are often ignored in modeling. Likely, some of these potentially overdesigned PH projects are based on models that are too conservative.

2) Using one set of numbers to define a standard--for any climate, any building size, any building type, will by default give you arbitrary (or you might say unscientifically determined) numbers, right? I actually find this aspect of PH quite compelling--while the numbers might be somewhat arbitrary, there are just 3 of them (compare that to a green building checklist!) and they provide something simple, solid and absolute to help guide decisions and provide a sense of how a project is doing. It's up to the project team (or wise consultant) to have some perspective about the numbers and decide whether it makes sense to achieve them "at any cost" for a given project. While I would like to see some adjustments made for climate & occupancy types, there's power in the simplicity of the PH criteria.

3) The fact that a building standard can inspire such passionate debate is amazing, and very telling about the compelling nature of PH! What nationwide "movement" have we seen that causes builders to work double-time to fanatically airseal. Overkill on such a project, perhaps--but who cares. I've seen PH transcend what's logical/pragmatic/cost-effective and give many people in this industry renewed passion for something they long ago forgot they loved. I'm all for us running with it, missteps and wrong turns and all. Let's keep constructive debates going, but not get caught up in fighting ghosts.

Apr 6, 2011 5:01 AM ET

Response to Katy Hollbacher
by Martin Holladay

Great post! And thanks.

As you might have guessed, I'm a big proponent of the Passivhaus standard, which is why I want to see the standard changed and improved -- and why exaggerations pain me. It's exciting to see these projects get built.

Apr 6, 2011 2:27 PM ET

An e-mail from Gary Proskiw
by Martin Holladay

Today I received an e-mail from Gary Proskiw, one of the authors of the study mentioned in Solplan Review and cited in my speech in Olympia. Proskiw wrote, "Someone just sent me your article in Green Building Advisor and I must say you are right on the money. Designing a Net Zero Energy House is easy, the trick is doing it without spending a truckload full of money. I have been working on the whole business of NZEH optimization for a while and have concluded that many of the things we are doing may, or do not, make sense."

Gary kindly agreed to allow GBA to publish the presentation that he and Anil Parekh gave at the BEST 2 conference in Portland, Oregon, in April 2010. Here it is: Optimization of Net-Zero-Energy Houses

Apr 6, 2011 3:04 PM ET

Economics of low-energy
by Jesse Thompson

To add even more variables to the conversation, so much of what we're talking about is based on ever-shifting costs as well. The Passivhaus standard was developed at a time when PV was much more expensive than it is currently (early 1990's).

I was reminded of this when we had to revise our net-zero design spreadsheet this week and dropped the price per installed kW of PV from $8,000 to $5,000 before tax credits. Insulation prices sure aren't dropping that quickly, in fact they seem to rise every time oil goes up in price...

The current PV cost curve may not continue, but it's currently behaving in a way that is disruptive to conservation economics.

Apr 6, 2011 3:24 PM ET

Edited Apr 6, 2011 3:25 PM ET.

Dropping PV prices
by Martin Holladay

You're right. But designers of net-zero-energy houses can take comfort from one level of certainty: they know exactly what their energy costs will be. Other designers have to scratch their heads and throw darts at the wall as they try to guess what energy prices will be in 15 years. Not designers of net-zero-energy homes: they know that they are designing a building that is optimized for a known energy price. That price is the cost of electricity generated by a PV array purchased at today's price for PV modules.

Apr 6, 2011 4:52 PM ET

by David White

i regret that i haven't taken enough time to read the full article or all the comments. however, i'd like to address some of the apparent demerits.

"Calling these superinsulated houses 'passive' is problematic." i used to work for a company called Transsolar and people frequently harrassed me about the fact that my company didn't design solar systems. one even suggested that i design solar systems for trannies. let's get over it. passive solar houses have heating systems too, and we don't complain about that, do we? the Passive House name is a matter of history - it stemmed from a research project to improve comfort in unheated houses in china.

"Delivering heat through ventilation ducts makes no sense." i believe the original intention of PH was to deliver heating via the fresh air supply, and it did work, and continues to work in many cases. if it leads to the elimination of a furnace and forced hot water distribution system without loss of comfort, that seems to make sense to me. not to say that i'm opposed to recirc.

"The annual space heating limit of 15 kWh/m²∙year is arbitrary." Juergen Schneiders at PHI told me that the original definition of PH, "a house that can be heated only by heating up its fresh air supply," led to overventilated houses in some cases, so first a peak load limit, and later an energy standard were set to close the loophole. 15 kWh/m2a is about what a house needs if it can be heated by its fresh air. this varies a lot with climate and especially glazing ratios. but it's not arbitrary.

i was disappointed to read these "demerits" because the information is freely available.

Apr 6, 2011 5:16 PM ET

Response to David
by Martin Holladay

I'm sorry to hear that my article disappointed you.

On point one, your advice is "get over it." That doesn't sound like disagreement with my point -- just an acknowledgment that the problematic name has been in use so long that it's too late to change. Unfortunately, however, this problematic name is still leading to misstatements, including a whopper -- the Passivhaus Institut's definition of a passive house, prominently featured on its Web site: a passive house is “a building in which a comfortable interior climate can be maintained without active heating and cooling systems.” As long as these misstatements continue to be promulgated by the Passivhaus Institut, I'm not going to "get over it."

On point two, you say that delivering space heat through ventilation ducts "continues to work in many cases." I agree; I don't dispute that. I object to the continuing presence on Passipedia of a passive house definition that says that space heat MUST be delivered that way.

On point three, you note that the origin of the heat load limit is the requirement that space heat be delivered through ventilation ducts. This is circular reasoning, especially if it is indeed true that the Passivhaus Institut has rescinded the requirement that space heat be delivered through ventilation ducts. In light of the irrelevance of the requirement that space heat be delivered through ventilation ducts, your explanation strikes me as arbitrary.

Apr 6, 2011 8:29 PM ET

Gary Proskiw's Presentation
by Daniel Ernst


In Gary's presentation he mentioned that they assembled 50 different Energy Conservation Measures (ECMs), then evaluated those measures against their PV Value Index---in four different climates, using three different house designs.

Do you know if the detailed information from this study is available to the public?

I looked on the NRCan website, only found mention of NZE cost optimization here:


Apr 6, 2011 10:55 PM ET

why only the PV vs foam comparison?
by deniz bilge

My comment regards homes in the mostly heating climate zones. PV vs underslab foam costs have been compared, but why isn't the discussion including solar thermal? (unless I missed that comment) I haven't done any math, but off the top of my head, I can't see why not install R-20 below slab insulation, then heat pex and run glycol through the collectors. The insulation wouldn't need to be as critically sized, nor would the relatively high PV costs come into play. 1 more point: I'm sure I'm the only nut who actually cares about environmental impact, but less foam = more environmentally responsible.

Apr 7, 2011 5:21 AM ET

Edited Apr 7, 2011 5:26 AM ET.

Response to Deniz Bilge
by Martin Holladay

Although solar thermal equipment appears at first glance to be more cost-effective than PV equipment -- because of all the BTUs you can collect in July -- it turns out that when used for space heating, solar thermal equipment is usually LESS cost-effective than PV. There are two reasons for this:

1. Most of the energy collected by a solar thermal system is collected during the summer, when it isn't needed. Storing heat energy for more than three or four days is very difficult and expensive.

2. Net-metered PV systems have a wonderfully efficient storage system -- the grid. As long as a homeowner has access to the grid and is able to sign a net-metering contract with the local utility, 100% of all PV energy is credited to the homeowner. (This contrasts sharply with the owner of solar thermal equipment, who collects a lot of energy that can never be used.)

I discussed this issue at length with the designers of the Riverdale net-zero energy house in Edmonton, Alberta. I reported my findings in the September 2008 issue of Energy Design Update. Here's what I wrote:

“The Riverdale design team assumed that an active solar thermal system was an essential component for a zero-energy house in Edmonton. As the project progressed, however, the solar thermal system became increasingly large and complex. ‘Even though we made the house envelope as efficient as we could, so that the house could be heated at minus 32 degrees Celsius with the equivalent of six hair dryers, we were still amazed at the size of the solar thermal system we needed,’ [Gordon] Howell told EDU. ‘We needed to extend the solar thermal collectors and the PV array beyond the roof line. We were also surprised at the huge complexity of the solar space heating system. We really did not expect solar space heating to be this complex.’

“[Peter] Amerongen echoed Howell’s observation. ‘We spent more on solar thermal than we ever expected,’ said Amerongen. ‘The solar thermal system is not hugely practical. We have a fair amount of technology chasing small amounts of energy, going after the last little bits of thermal load. When it comes to chasing net-zero energy, in some ways it actually makes more sense to go 95% of the way on a number of houses than to go 100% of the way on a single house.’

“As the building neared completion, Howell began to doubt the wisdom of including a solar thermal system. Howell recounted, ‘I said, “Peter, this is ridiculous. Let me go back and see what would happen if we had eliminated the solar thermal equipment.” After running the numbers, I was dumbstruck. The cheapest house would have been a house without a solar thermal system, using just PV and geothermal heat. That would have cost $8,000 less than what we did. If we went with a PV-only system — with no solar thermal and no geothermal, only passive solar heat, electric resistance heat, and a PV system — it would have cost only $1,000 more than what we are doing now, and it would be hugely less complex. I was stunned with this. The increased area of the PV array would have been identical to the area of the existing solar thermal collectors, and the PV array could have been integrated into a single sloped roof.’

“Heating a house with PV instead of a solar thermal system is counterintuitive. ‘PV is way more expensive and less efficient than solar thermal,’ Howell noted. Although a large solar thermal system can collect a lot of heat during the summer, the heat is difficult to store. ‘The big difference between PV and solar thermal is that we haven’t figured out how to convert solar thermal heat to natural gas and feed the gas back to the grid,’ said Howell.”

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