GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon
Musings of an Energy Nerd

Redefining Passivhaus

The Passive House Institute U.S. takes a stab at developing new passive house standards for North America

Image 1 of 3
The committee charged with developing new passive house standards for North America ran energy simulations that modeled a variety of envelope measures for homes in a great variety of climates. Each yellow dot on the map shows a location that was simulated in the study.
Image Credit: Images #1 and #3: Building America
The committee charged with developing new passive house standards for North America ran energy simulations that modeled a variety of envelope measures for homes in a great variety of climates. Each yellow dot on the map shows a location that was simulated in the study.
Image Credit: Images #1 and #3: Building America
This graph shows how BEopt software can help designers optimize the envelope design of a house. The X axis shows energy upgrade options; the Y axis shows total annual costs for a homeowner. Energy-efficiency measures can lower total costs to the owner of a new home — up to a point. Beyond that point, further investments in insulation or better windows will result in higher mortgages costs — more than the energy savings justify.
Image Credit: Image #2: NREL
This table shows proposed energy targets for a new North American passive house standard. The first column shows climate zones.

In January 2012, Katrin Klingenberg, the founder of the Passive House Institute U.S. (PHIUS), announced that her organization would develop a new passive house standard for North America — a standard that differed from the Passivhaus standard developed in Darmstadt, Germany.

Writing in her blog in 2012, Klingenberg explained that “it’s time to allow for a modification process to the rigid annual heating and cooling requirement of less or equal to 15 kWh/m²•yr… for the North American continent’s more extreme climates… This idea that we need to adapt the standard to various regions has taken root around the world from domestic energy experts like Martin Holladay, Alex Wilson, and Marc Rosenbaum and to Passive House groups from other countries, like the Swedes.”

Almost two years later, Klingenberg made another announcement: the work required to develop the new standard would be partly funded by U.S. taxpayers (through the Department of Energy), and one of the contracts for the required study would be awarded to the Building Science Corporation of Westford, Massachusetts.

A few weeks ago, Klingenberg’s first goal was reached when the DOE-funded paper (“Climate-Specific Passive Building Standards”) was published. The report has three authors: Betsy Pettit (from Building Science Corporation), Graham Wright (from PHIUS), and Katrin Klingenberg.

In effect, the paper is a draft for a proposed new passive house standard. PHIUS is now inviting the public to comment on the draft standard; after the public comments are reviewed, the standard may be modified before being adopted by PHIUS.

What is a passive house?

A few years ago, PHIUS cut the umbilical cord linking it to Germany. Since then, the U.S. organization has no longer been bound by the German definition of a “Passivhaus.” Because if its recent independence, PHIUS now has a chance to ask an important question: what, exactly, do we mean by a “passive house”?

Back in the late 1970s, the term “passive” was used to differentiate two different approaches to solar architecture. The “active solar” approach included either a system with fluid-filled solar collectors and a pump that circulated fluid from a storage tank to the collectors, or a system with a fan that circulated air from a bin filled with rocks to roof-mounted solar-air collectors.

The “passive solar” approach did not include any pumps or fans. Instead, it depended on oversized south-facing windows, interior thermal mass, and properly sized roof overhangs.

While the latest PHIUS document hints at this early distinction between the “passive” and “active” approaches — the new paper says that “PHIUS acknowledges that passive house was born in Canada and the U.S. in name and concept” — it has come up with a new definition of the “passive” approach. The draft document states: “The view of what constitutes a passive measure … includes fan- and pump-assisted devices such as HRVs, earth air tubes, brine loops, and whole-house fans, in addition to insulation, air-sealing, overhangs and such.”

For designers who are old enough to remember the 1970s, such a definition is startling. When I saw this ahistorical definition, I felt like putting my forehead on the table. But by now, any attempt to reclaim the old definition of a “passive solar house” seems doomed to failure. Evidently, the muddying of the waters that began when Dr. Wolfgang Feist established a definition for “Passivhaus” in the 1990s can’t be fixed. It’s now too late to untangle the string.

The new PHIUS document notes, “As passive house standard adaptations go, the one described here is relatively far-reaching. Nevertheless it retains all defining characteristics of a ‘passive’ building.” If only the confused reader knew what a “passive building” is, perhaps these two sentences might make sense.

For the time being, however — at least until the new standard is finalized — we’ll all have to shake our heads in dismay and avoid asking the embarrassing question of what anyone means these days when they use the phrase “passive house.”

What is wrong with the existing Passivhaus standard?

The new PHIUS document alludes to at least 14 problems with the existing Passivhaus standard developed in Germany.

1. A single rigid standard — one requiring a maximum peak heating load of 10 W/m² or a maximum annual heating energy budget of 4.75 kBtu/ft²yr — can’t possibly represent the “economic optimum” approach for every location on the planet. As the draft proposal notes, “PHI [the Passivhaus Institut in Germany] claims that the ‘economic optimum’ occurs at 10 W/m² peak heat load or the 4.75 kBtu/ft²•yr annual heat demand everywhere in the world. ‘That can’t be right’ is the objection.”

2. North American climates aren’t comparable to European climates. While the number of heating degree days (which influence the annual heating fuel budget required for a building) for many locations in North America is similar to the number of heating degree days in European locations, North American locations often have higher design heating loads (which influence the size of the needed heating system). As the PHIUS paper notes, “the relation between degree-days and peak design temperature varies by climate; they are but weakly correlated. Away from the [Atlantic and Pacific] coasts [in North America], peak design conditions are relatively harsh compared to degree-days.”

The paper also notes, “PHI literature usually quotes -10°C/14°F as a peak load design temperature for central Europe … In the mid-continental United States, places with similar heating degree-days to Germany have much harsher design temperatures.”

The fact that many North American locations have colder design heating loads than German locations means that our thermal envelopes have to include much more insulation to meet the 15 kWh/m²•year (4.75 kBtu/ft²•yr) heating energy budget than would be the case in Germany. The insulation required to meet the German energy budget are so thick that they aren’t cost-effective.

3. “Tunneling through the cost barrier” didn’t work. Wolfgang Feist, the German physicist who developed the Passivhaus standard, claimed that Passivhaus levels of airtightness and insulation save money, because a Passivhaus building doesn’t need a conventional heating system. This idea — that it is possible to add so much insulation to a building that savings can occur by simplifying the building’s HVAC system — was termed “tunneling through the cost barrier” by Amory Lovins.

The “tunneling through the cost barrier” idea is like a unicorn: often described but rarely seen. As the PHIUS report notes, “In North America, ‘tunneling through the cost barrier’ was not achieved. Unlike Germany, there is not such a clear breakpoint where an expensive baseline boiler and hydronic distribution system (the typical heating system in Europe) can be eliminated for great savings.”

Compared to conventional buildings, most Passivhaus projects in North America have seen significant cost premiums rather than cost savings. The PHIUS report notes, “In a 2009 article, John Straube critiqued PHI’s standard. While this article contained some misunderstandings, its basic point was accurate that in ASHRAE Climate Zones 5 through 7 in North America, the standard is not economically justifiable, by and large.”

4. When used in North America, the existing Passivhaus standard results in overglazed buildings that sometimes overheat. Several GBA articles, include one that I wrote in 2012, have noted that many Passivhaus buildings in the U.S. have too much south-facing glazing. The new report acknowledges that this is indeed a problem: “PHIUS+ certification that uses European energy metrics and specific standards as written has resulted in (broadly speaking) passive-solar-esque designs with a tendency to overheating, and discouragingly high cost premiums.”

5. The existing standard’s default values for miscellaneous electrical loads are unrealistically low. PHIUS would fix this problem by setting new (more realistic) default values for electrical loads.

6. The existing standard’s default value for domestic hot water use is unrealistically low. PHIUS would fix this problem by setting a new (more realistic) default value for domestic hot water use.

7. The European method of calculating a building’s floor area is quirky and cumbersome. The PHPP spreadsheet that determines whether a proposed design gets a “ja” or “nein” has an unusual definition of floor area. The definition is taken from a German law, the Wohnflächenverordnung, that defines floor area as the interior area of a building, excluding the following elements: the exterior walls, the plaster on walls, the area of chimneys, the area of interior partitions, the area defined by an interior door, the area of columns, and the area taken up by stairs with more than three steps. Other caveats: rooms with a ceiling height below 6.6 feet are excluded (although rooms with ceiling heights between 3.3 feet and 6.6 feet in height are added at 50 percent of the area); the rooms must be within the thermal envelope (so that three-season rooms and garages are excluded); and storage and mechanical rooms inside the thermal envelope are included at 60 percent of the area.

It’s safe to say that no one in North America (other than Passivhaus consultants) defines a building’s floor area following the Wohnflächenverordnung rules. The new draft document from PHIUS proposes a new, easier-to-calculate method for determining a building’s floor area.

8. The existing Passivhaus standard discourages the use of North American HRVs and ERVs by imposing an unjustifiably harsh method for de-rating published efficiency ratings for these North American appliances. To correct this problem, the draft standard proposes a new formula for calculating the efficiency of HRVs and ERVs.

9. The existing Passivhaus standard imposes a source energy factor for grid electricity that is based on the European grid, not the North American grid. The draft standard proposes a new, more realistic source energy factor for North America.

10. The existing Passivhaus standard bases its source energy limit on a building’s area rather than on the number of occupants. The draft standard notes that a per-person limit makes more sense.

11. The existing Passivhaus standard allows the energy produced by an on-site solar thermal system, but not the energy produced by an on-site PV system, to “count” toward meeting the standard’s energy targets. The draft standard will correct this problem by allowing some of the energy produced by an on-site PV system to be counted.

12. The PHPP spreadsheet assumes a high (and possibly erroneous) rate of heat loss in winter through concrete slabs on grade. The PHPP calculations for heat loss through a slab on grade differ from similar calculations made by North American energy modeling programs. Because of this discrepancy, the PHPP software ends up validating building designs that include very thick layers of sub-slab rigid foam — foam that is so thick that the approach leaves North American observers scratching their heads. Here’s how the problem is described in the PHIUS paper: “[The] Ground contact calculation protocol [is] very different between EnergyPlus dynamic and PHPP/WP static. Anecdotal evidence suggests that the EnergPlus’ method predicts a lot less heat loss to the ground than ISO 13370-based static calculations. If so and if EnergyPlus is right, then designers using PHPP/WP are over-insulating their floors.” Although the issue was raised by the technical committee, no conclusions were reached. The paper simply notes, “This discrepancy needs to be confirmed and corrected.”

13. The existing Passivhaus standard is based on modeled performance, not measured performance. While hinting that this problem exists, the committee that drafted the new proposed standard decided not to address it. The draft paper notes, “The proposed adapted standard is still performance-based, that is, based mostly on modeled performance, as opposed to a prescriptive approach or an outcome-based approach.” One proposed solution to this problem would be to delay awarding Passive House certification until homeowners could show one year of energy monitoring data that matched or beat the modeled projections; the committee did not adopt this suggestion.

14. The existing Passivhaus standard includes a small-house penalty. Because larger homes have a smaller surface-to-volume ratio than smaller homes, it’s easier for a large home than a small home to meet the Passivhaus standard. The committee that drafted the new standard alluded to the problem but decided not to fix it: “The studies [made by the PHIUS committee] are predicated on providing housing that is typical for the North America market (i.e. the three-bedroom house). More efficient forms of housing, such as multifamily units, will have an easier time meeting the criteria, while less efficient forms, such as detached ‘tiny houses’ will have a harder time of it.”

Did the committee aim for cost-effectiveness?

The authors of the report refer to themselves as the technical committee (TC for short). While many people assumed that the committee would pay attention to cost effectiveness, in fact the authors left themselves a little wiggle room. Instead of creating new standards that are cost-effective, the committee decided to aim for standards they call “cost-competitive.” Here’s what the authors wrote: “The reported work is an up-to-date, independent study of how much investment in passive measures can be economically justified as cost-competitive, if not strictly cost-optimal.”

The main tool used for this determination was BEopt software. (For more information on BEopt, see BEopt Software Has Been Released to the Public.) BEopt software aims to optimize the specifications for a building envelope, so that the cost to the owner of a new home for utility bills plus the mortgage are as low as possible (see Image #2, below). The software recognizes that beyond-code improvements to a home’s envelope can result in lower total costs, even when the mortgage is larger than it would be for a code-minimum home — but only up to a point (the cost-optimum point).

The PHIUS committee decided that there were reasons to pay for additional envelope improvements, even if these envelope improvements go beyond the cost-optimum point and result in higher total costs for the homeowner.

Here’s the approach that the committee took: “A human judgment call was made, as to the point of deepest energy savings feasible, cost-competitively — location by location. … The PV start point would be a defensible level at which to set the criteria. But it may be appropriate to choose a more aggressive point on the cost-optimal curve, that is, one still cost-competitive but with less annual dollar savings. …The rationale is that passive measures are better for the building owners and occupants than renewable generation alone. They increase the building’s resilience to utility outages, by minimizing heat losses and thus allowing interior temperature ‘coasting’ during outages. … The TC [technical committee] as a whole was inclined to forgo some annual dollar savings if more peak load reductions could be realized. … One could argue that pushing past the cost optimum is actually a conservative approach given the uncertainty of … future developments and possible climate risks. … The TC agreed upon the following heuristic for setting the criteria: … Note the knee of conservation-only cost curve and go a little past it, to where conservation is heading into diminishing returns.”

In other words, expensive envelope measures are sometimes defensible, even when the cost of these measures is somewhat higher than can be justified by the expected energy savings.

A modeling exercise

The process described above — using BEopt software to determine which beyond-code envelope improvements result in a house with the lowest total cost for the homeowner — was applied to a “typical” two-story, three-bedroom house. Once this cost-optimum point was determined, the committee used human judgment to decide what additional envelope measures to include beyond the cost-optimum point.

The modeled house was an all-electric house with a slab-on-grade foundation, a vented attic with cellulose on the attic floor, and walls insulated on the exterior with a continuous layer of EPS foam. The technical committee decided to include a “constraint,” namely that windows had to have a relatively low U-factor — low enough to ensure that the interior surface of the glass stayed at 60°F or warmer during the winter. The committee wisely decided that “there will be no subsidizing performance upgrades by cheapening finishes. This strategy, while effective if you can get it on a project, is unfair to include in the studies.”

The energy performance of this house was modeled in over 100 North American locations (see Image #1 at the top of the page).

The committee’s recommendations

The fundamental problem that the committee set out to address is that the existing Passivhaus standard, when implemented in North America, often results in buildings that aren’t cost-effective. These Passivhaus buildings have insulation that is so thick, and windows that are so expensive, that the cost of the insulation and window upgrades is much higher than the value of the energy that will be saved by these upgrades over the life of the building.

In response to this fundamental concern, the committee proposed different energy use targets for space conditioning and different window U-factor specifications for a variety of climates. These proposed targets and specs are shown in Table 8 of the committee’s report (see Image #3, below).

While the existing Passivhaus standard allows designers to aim for either a maximum annual energy budget for space conditioning of 15 kWh/m²•year or a maximum peak heating load of 10 watts/m², the proposed new standard will require that both targets — a target for the annual energy budget for space conditioning and the target for maximum peak heating and cooling loads — be met. As the report notes, “We propose to set limits on annual heat demand and peak heating load, as well as annual cooling demand and peak cooling load. So the criteria would read: Annual heating demand < A, and Annual cooling demand (sensible+latent) < B, and Peak heating load < C, and Peak cooling load < D. These would vary by climate.” Instead of the current Passivhaus space heating energy budget of 15 kWh/m²•year (equivalent to 4.75 kBtu/ft²•yr), the committee proposes less rigorous targets for Climate Zones 5 through 8 and for some locations in Climate Zone 4. These new proposed targets would range from 5.6 kBtu/ft²•yr in Climate Zone 5B to 13.2 kBtu/ft²•yr in Climate Zone 8. The committee proposed more rigorous space heating budgets for Climate Zones 1 through 3, ranging from 0 kBtu/ft²•yr in Climate Zone 1A to 3.0 kBtu/ft²•yr in Climate Zone 3A.

Cooling energy budgets would also be adjusted, and would range from 0.2 kBtu/ft²•yr in Climate Zone 8 to 18.6 kBtu/ft²•yr in Climate Zone 1A.

These proposed space heating and cooling energy budgets are not set in stone. In fact, the paper notes, “the TC [technical committee] doesn’t think a tabular approach like this [that is, an approach like the one presented in its report] is granular enough for program use.” Presumably, a more refined method will be proposed before any new Passive House standard is approved by PHIUS.

In addition to these proposed space heating and cooling energy budgets — targets that cannot be exceeded — the committee proposed climate-specific peak heating load targets and peak cooling load targets.

The peak heating load targets range from 1.75 Btuh/ft² in Climate Zone 1A to 8.4 Btuh/ft² in Climate Zone 8.

The peak cooling load targets range from 10.7 Btuh/ft² in Climate Zone 2B to 4.9 Btuh/ft² in Climate Zone 3C.

The recommended maximum glazing U-factor for windows ranges from U-0.40 in Climate Zone 3C to U-0.10 in Climate Zone 8. These proposed maximum U-factors are driven by occupant comfort concerns, not energy budget concerns.

Other recommendations

In addition to the proposals listed above, the committee made several other recommendations.

A new way to calculate floor area. Here is the new proposed definition: floor area will be “measured on the interior dimensions of the passive house thermal envelope, drywall-to-drywall, where ceiling height is greater than or equal to seven feet. This specifically includes stairs and interior partitions, as well as baseboards and cabinets. It specifically excludes open-to-below.”

A new way to calculate the efficiency of HRVs and ERVs. The committee has set itself the goal of making this change, but a proposed solution has not yet been published. The report notes that “the efficiency ratings of heat-recovery ventilators aren’t apples-to-apples comparable between PHI and domestic institutes (HVI and AHRI). Up to now PHIUS has been using a rule of thumb from PHI, ‘subtract 12% from the sensible efficiency of non-PHI-rated units.’ The TC [technical committee] recently determined more nuanced adjustments to HVI and AHRI ratings that bring them closer to comparability with PHI rating, and the 12% deduction remains only for units that don’t have any third-party rating. This work is also beyond the scope of this report and is being written up separately.”

A new default value for domestic hot water use. The proposed new standard assumes that occupants “Use hot water as per BA [Building America] assumptions (~50% higher than PHPP).”

A new default value for miscellaneous electrical loads. The committee recommended that “For residential projects, the defaults for lighting and plug loads [should] increase to 80% of RESNET levels.” This is a big change: “These [new default levels] are about six times the PHPP defaults but lower than Building America baseline home. … The low PHPP defaults are grossly unrealistic, a discrepancy that must be fixed.”

This change will have several interesting consequences. “Such an increase in residential lighting and plug load defaults is a large change that makes it considerably harder to meet the source energy target. … Under the PHI protocol [that is, the existing Passivhaus standard], the space conditioning criteria were usually the limiting factor, while the source energy target was relatively easy to meet. But with higher lighting and plug load defaults, and potentially higher space conditioning thresholds, the source energy limit could become the limiting factor.”

A new source energy cap. The source energy cap is the maximum amount of source energy that a Passivhaus project can use. (For more information on the distinction between source energy and site energy, see Understanding Energy Units.) In the existing Passivhaus standard, the source energy cap (120 kWh/m²•year) is based on a building’s area. PHIUS proposes a change: “For residential projects it is appropriate to change [the source energy cap] to a per-person budget, based on a fair-share of the atmosphere consideration. Occupancy is therefore taken to be the number of bedrooms plus one, per dwelling unit.” Elsewhere, the report notes, “Straightforward conversion of the 120 kWh/m²•year limit times 35 m²/person standard occupancy would give a limit of 4,200 kWh/person•yr. A review of previously certified [Passivhaus] projects showed a median source energy design for 4,100 kWh/person•yr, but with lighting and plug load defaults adjusted to RESNET levels, the median would have been almost 6,600 kWh/person•yr.”

In other words, the new proposed source energy cap is so stringent that many certified Passivhaus buildings would be unable to meet it. The committee therefore came up with a compromise solution, proposing that “as a shock absorber, the source energy limit should be temporarily relieved [changed] to 6,000 kWh/person•yr, returning [rather, changing again] to 4,200 by a date to be determined.”

A new source energy factor for grid electricity. The committee recommends changing this energy factor from 2.7 to 3.1. The report notes, “The U.S. electric grid is known to have source energy factors ranging from 2.374 to 3.549 depending on the major interconnect region, with a national average of 3.138. For the sake of simplicity and a level playing field, it is reasonable to use the national average. In recognition that the grid has probably gotten cleaner since the report was published, one can round down.”

A change allowing electricity produced by PV arrays to “count” toward Passive House targets. The committee decided to allow PV electricity produced on site to “count,” but only if the PV electricity is used on site simultaneously. The report notes, “Currently, the only renewable energy that ‘counts’ towards reducing source energy is solar thermal. The Committee agreed to put other renewable generation on the same footing if it is used as it is produced.”

New airtightness limits. Instead of setting an airtightness limit at 0.6 air changes per hour at a pressure difference of 50 pascals — the existing target — the committee proposed a new limit using different units. The proposed limit would be 0.05 cfm50 per square foot of gross envelope area. As the paper notes, this proposed change “allows the airtightness requirement to scale appropriately based on building size. Before, a larger building that met the 0.6 ach50 requirement could be in actuality up to seven times more leaky than a small single-family home that tested the same.”

More on airtightness

The PHIUS paper repeats a problematic claim made by Wolfgang Feist — namely, that “The airtightness requirement comes from consideration of building durability and mold risk.”

No convincing argument has ever been presented to show that the 0.6 ach50 target is necessary to prevent condensation, mold, or rot. On the contrary, there is plenty of evidence that buildings with air leakage rates of 0.6 to 2.0 ach50 are performing very well.

Instead of abandoning Feist’s basis for establishing an airtightness target, the PHIUS committee appears to have embraced it — while simultaneously noting that the target will need to be changed if the argument for its basis is retained.

The paper notes, “The top priorities for future work at this point are: … Studies on relaxing the airtightness criteria by climate. Again, the airtightness requirement is driven by moisture risk (energy savings being a side benefit). It stands to reason that the danger threshold would be climate-dependent. Also, it may be appropriate to revisit the field testing protocol: perhaps the test should be done two different ways — one for energy modeling purposes being realistic about leakage in normal operation, and another protocol for durability, focusing on leakage through the assemblies, with more of the nonthreatening things like door thresholds and vent dampers taped off. … The airtightness requirement was reconsidered on the basis of avoiding moisture and mold risk, using dynamic hygrothermal simulations to be published elsewhere.”

It’s all about electricity rates

As an aside, the paper includes two key sentences that are startling: “In places with expensive energy, everything was affordable in a sense: even [envelope] measures that were deep into diminishing returns still showed cash flow. In places with cheap energy, distressingly little was affordable.”

The implications of these two sentences are profound. If the PHIUS committee expects its report to be taken seriously — and clearly it does — then readers are owed a much deeper exploration of the implications of these two sentences than the report provides.

It’s a fact that upgraded envelope measures aren’t cost-effective in areas with cheap electricity. Anyone who is developing a green building rating program needs to address this issue head-on. The members of the PHIUS committee are to be commended for tackling the thorny problem of cost-effectiveness, but their efforts have led them down an alley to a place where they didn’t want to end up.

The PHIUS paper suggests several reasons (including increased resiliency) to defend envelope measures that aren’t cost-effective. But the committee hasn’t clearly addressed the fact that areas with cheap electricity don’t really need fancy thermal envelopes. This fact becomes especially stark during historical periods (like this one) when energy prices (including prices for PV power) are dropping.

No one knows what a “passive house” is

This dilemma points to an unresolved question: what, exactly, is a “passive house”? If PHIUS believes that a passive house can include a furnace, a ductless minisplit, an active solar thermal system, an HRV, and a buried brine loop hooked up to a circulating pump, it appears as if we have entered an Orwellian world where “passive” means “active.”

This dilemma is especially poignant for PHIUS, since PHIUS wants to distinguish the “passive house” approach from the “net zero energy” approach. But unlike the members of the PHIUS committee, who have yet to come up with a cogent definition of “passive house,” at least the members of the net-zero-energy community know how to define a net-zero-energy house. For the net-zero-energy designer, an envelope measure makes sense if the value of the energy saved by the measure exceeds the value of the energy saved by a PV system that costs as much as the envelope measure under consideration.

If the PHIUS committee adopted this approach, at least there would be a rational way to defend upgraded envelope measures in regions where energy is so cheap that “distressingly little is affordable.” The only remaining problem for PHIUS (if they took this advice) is that there would no longer be any difference between the net-zero-energy approach and the “passive house” approach.

The committee deserves praise

Katrin Klingenberg and the other members of the PHIUS technical committee have embarked on a very interesting journey. Their willingness to listen to technical arguments undermining the foundations of the Passivhaus standard has been remarkable, especially in light of the fact that most of the committee members have been proponents of the Passivhaus approach for many years. The committee’s proposed changes represent useful and defensible improvements to the Passivhaus standard.

It will be interesting to see whether the new PHIUS construction standards gain traction in the U.S. over the coming years, or whether the PHIUS approach will remain (as it is now) a little-used certification program that is difficult to implement without the help of a consultant trained in the use of a complicated spreadsheet with a daunting number of inputs and calculations.

Is the concept compelling enough to attract homeowners?

If homeowners choose to follow the PHIUS path, what kind of a house will they end up with?

It won’t be passive. Like most homes in the U.S., it will require active HVAC equipment to supply space heating, cooling, ventilation, and domestic hot water.

It won’t have the lowest possible ownership cost (that is, mortgage cost plus utility costs), because the PHIUS committee has decided to require investments in envelope measures that push the cost of a new home beyond the cost-optimum point.

It probably won’t be a net-zero-energy house, because the PHIUS committee isn’t considering a requirement for a PV array that can balance annual energy use.

Time will tell whether there is much of a market for this type of home in the U.S.

Martin Holladay’s previous blog: “Solar Thermal Is Really, Really Dead.”

Click here to follow Martin Holladay on Twitter.


  1. Ethan Fahy | | #1

    Another standard, another chance to post this gem:
    As someone interested in having a home built someday I enjoy following the progression of these standards and ideas, but amid the flurry of figures I tend toward throwing my hands up and just demanding a pretty good house.


  2. Skip Harris | | #2

    Head-scratcher, indeed
    Excellent post, Martin.

    I applaud the PHIUS for allowing PV! With it getting cheaper and cheaper, one can oversize systems to gain 90% or 95% of energy from that source, dumping excess into heating or cooling the moderate thermal mass of the house while the sun shines, sidestepping the source-energy penalty.

    One might sidestep uncertainty about future energy costs by assuming all being electricity at $0.15/ as that seems to be a close approximation for PV and other. It is hard to imagine that low prices (coal in Wyoming, for example) will not rise and high prices (Hawaii) moderate as cheap PV lets folks defect from expensive power.

    That said, it IS hard to figure out just what one gains by going with the PHIUS standards. They claim "Comfort. Quality. Efficiency. Resiliency. Affordability. Now." but one can easily show that none of these are really addressed in a spherically defensible way and one ends up with a "standard" that pretty much simply provides an expensive plaque and not much more compared to a net zero or PG house.

    That said, it is hard to imagine a solid standard that would fit the PH moniker. Perhaps it could be a house that "remains liveable" even if power goes out for a week in the worst part of the year, but it needs a simple, attractive, and all-around sensible definition... that remains sensible in practice. I hope they can do it, but sometimes you need to stop tweaking your spaghetti-code and start fresh.

  3. Daniel Young | | #3

    $/kWh for PV
    Dustin, not sure where you're located, but generally PV's cost for energy is a lot less than $0.15/kWh.

    "...$0.15/ as that seems to be a close approximation for PV and other..."

    A very small system can come in at $0.15/kWh with no economies of scale behind it. But your average residential PV system (5-6kW) comes in at $0.10/kWh or less depending on your specific details. I don't have a chart saying what the average $/kWh is for utility power in each state, but i believe that is lower than the Utility in the majority of the US.

    I calculate cost/kWh using the 25yr performance warranty held by almost all PV module manufacturers. If you want to define it differently, then maybe you're $0.15/kWh is accurate. Also if you finance the array, it affects the cost as well.

  4. Shane Claflin | | #4

    A ceiling height of 6.6 ft. is 6 feet 7inches and 3/16ths roughly. 3.3 ft. is 3 feet 3 inches and 5/8th if you round it to .625. converting decimals to inches gets hairy.

  5. Ven Sonata | | #5

    Reply to Daniel Young
    Pv cost per kwh. It's good to say how we get the price per kwh from pv, then anybody can use the math. Here is one way. An easy average production from a one kwh pv array fixed optimal angle is about 1500 kwh per year( in Arizona 1800). Though pv warranty is 25 years, they will last and produce much longer with only minor loss, however I will use 30 years times 1500kwh per year as 45,000 kwh production lifetime( very conservative). Each dollar per watt installed is equivalent to 2.2cents per kwh lifetime.( (1000 divided by 45,000) $1000 per kwh installed gives you electricity at 2.2cents kwh. But we are not done yet...don't celebrate. The rest of the system has a lifetime too. Wires and racking have even longer than 30 year lifespans...great! Now inverters are necessary, oh, oh. Inverters will cost you 30cents per watt and have a lifespan of 15 years. So a 1 kw inverter $300. You need two in 30 years so $600. So add 1.3 cents per kwh. Now we have 2.2 plus 1.3 = 3.5 cents plus another $1500 for labor and cost of racking and wiring. 3.3 cents kwh. Grand total 6.8 cents per kwh. Guaranteed for thirty years. So my calculation work out to $3.50 per watt installed at average 1500 kwh per year production for thirty years. That is a fantastic rate for electricity. By the way $3.50 is possible these days but on the low end.
    I should add a new thought. Micro inverters are now warranted for 25 years...the life of the panel, so the formula is easier to give all parts of the system a 30 year lifespan and soon installed rates on larger systems of say 5 to 10 kwh will be $3watt. At that rate 6.6cents per kwh...nothing competes with that. Note that I am estimating the pv panel price at $1 watt. You can get them as low as 85 cents now!

  6. Malcolm Taylor | | #6

    I agree. Carl Seville's recent blog about city ordinances mandating compliance with one of a range of "green" standards makes your cartoon even more poignant. Given the difference between the aims of programmes like Leed and Passive House I just wonder what, beyond a feel good factor, such rules are meant to achieve?

  7. George Hawirko | | #7

    Findings frome Mold Growing fron the Breath of Cave Visitors
    "The cave located at Santillana del Mar, in the Cantabria region, was closed in 2002 after damages had been reported to its polychrome prehistoric paintings from the carbon dioxide in the breath of the large number of visitors."

    RE: More on airtightness
    The PHIUS paper repeats a problematic claim made by Wolfgang Feist — namely, that “The airtightness requirement comes from consideration of building durability and mold risk.”

  8. Ven Sonata | | #8

    The bottom line is kwh sq ft
    Passivhaus allows what I consider an extravagant amount of total energy use per sq meter. 110 kwh per year. While they are impressive in their heating allowance, the bottom line is total energy used. Our house is about 30% more in heating demand than passivhaus standard per year (although we are in a 9000 heating degree day zone) but 70% less overall than passivhaus total energy allowable. Specifically the house is 1000 sq meters (10,000 sq ft) and uses 35,000kwh per year total. That does not even count the fact that 97% of electricity is provided by PV (we are off grid). We do not do without anything but we have thought through everything carefully. So this raises a major question mark about the whole vision of passivhaus. Although, don't get me wrong, many things I have done have been inspired by passivhaus ideas...but there is much more to explore. GBA and the Passive house group are a very canny and bright bunch of people, keep it up.

  9. Peter L | | #9

    A Great Start
    I believe the PHIUS movement is a great start to help push for a higher energy level in US homes. While we have the 2012 IBC and it's related energy codes, the Passive House goes above and beyond and in the end it will make for more energy efficient homes. If there is no "goal" or standard to attain for, people will usually not respond and build homes like they did 20 years ago.

    I know PH has it detractors and those who like to mock it and it's always frustrating to see the Green Building movement always fighting with itself. That phenomena can be seen here on GBA with people arguing about what is green and what isn't green. Everyone has their bias, that is a reality of being human. No matter what title or position they hold, they are bias to one way of building and hold to their own definition of what constitutes "green".

    I believe the PH movement will gain ground in the USA and the PHIUS is leading the way.

  10. User avater
    Aaron Birkland | | #10

    Active, Passive, and Tunneling through the ____ barrier.
    This article does a good job in explaining that both passivhaus standards are well-specified lines in the sand for building a house with unusually low energy consumption, but that these lines don't necessarily define the operating conditions that enable any specific observable phenomenon in occupant comfort, cost optimization, or energy usage.

    In my mind, it would be most logocal to tie a standard with 'passiv' in its name to some desirable 'passive' phenomenon. The article mentions that the German standard 'tunnels through the coat barrier' by eliminating the he need for an expensive hydronic heating system, but says there isn't an equivalent barrier in North America. Isn't there?

    Wouldn't the point at which a house no longer needs a distribution system for heating or cooling be a neat place to define a standard around? Such a point would be reached when a house can maintain comfort (say a maximum ∆T between living spaces, or something else that is quantifiable) using only a maximum of one point-source heating or cooling appliance per unit living area (story?). One could argue that relying completely on the conduction, convection, or radiation that naturally occurs in response to introducing a so gle heat source or sink makes sense to call 'passiv'.

    In facy, now I wish a house designed in such a way (with attention to room by room loads, and satisfying heat from a single point source per floor) had a name

  11. User avater GBA Editor
    Martin Holladay | | #11

    Response to Aaron Birkland
    You have proposed a new standard -- let's call it the "one point-source heating appliance only" standard.

    It's a perfectly reasonable standard, but lots and lots of homes comply with it -- including almost every leaky log cabin in Alaska equipped with a wood stove, as well as my own leaky, poorly insulated home (also equipped with a wood stove).

  12. User avater
    Aaron Birkland | | #12

    response to Martin

    I have a shed in the middle of a field that is net zero. May I blog about it :).

    In all seriousness, the "tunnelling through the cost barrier" section of the article doesn't quite make sense in relation to your response. It is asserted in the article that one (claimed) benefit of the passivhaus standard is that it renders hydronic heating systems commonplace in Europe unnecessary. Your comment implies that lots and lots of houses do not need to distribute heat and cooling, even leaky ones in severe climates. If this is true, then that implies that there really is no barrier to tunnel through (i.e. the hydronic systems that the PH was rendering unnecessary were never necessary in the first place.

    Are you indeed saying that the "tunneling through the cost barrier" is a unicorn, because the this barrier never existed in the first place? That being able to heat and/or cool a home so that all living space is is within a small ∆T from one another using single point-source per floor is generally unremarkable?

    For that matter, could Carter Scott have built significantly worse homes, and still maintained the same degree of comfort with just two ductless minisplits?

  13. User avater GBA Editor
    Martin Holladay | | #13

    Response to Aaron Birkland
    The point of my response is that it's tricky to write a standard. If you want to create a new standard, the "one point-source heating appliance only" standard, you may be surprised to find how many leaky buildings comply with your new standard.

    You issue you raise is complicated, and is often discussed on GBA. The following points are true:

    1. It can be argued that most European hydronic heating systems are, indeed, unnecessary. There are lots of ways to heat a house.

    2. Comfort expectations vary widely, so many families are perfectly happy with a single point-source heater. Other families have members who complain about room-to-room temperature differences.

    3. Tight, well-insulated homes with high-performance windows are less likely to have comfort complaints, or to suffer from large room-to-room temperature differences, than leaky, poorly insulated homes.

    4. Most building codes require the installation of a heating system that keeps every room in the house at a comfortable temperature. It's up to the local code inspector to determine how to enforce this provision, but it raises questions for some homes with a single point-source heater.

    When I compared the idea of "tunneling through the cost barrier" to a unicorn, this is what I meant:

    1. Most Passivhaus buildings in North America have relatively expensive HVAC systems. Many include Zehnder HRVs that cost between $5,000 and $7,000 to install, as well as a heating system and/or a cooling system. (To take a handy example, GBA is now running a construction blog by Alexi Arango. The HVAC equipment for his 1,000-square-foot Passivhaus residence cost $19,224. Plenty of contractors who build conventional tract housing can install all of the HVAC equipment needed for a single-family ranch house for much less than that.)

    2. Wolfgang Feist chose the word "Passivhaus" deliberately, to imply that these buildings don't require active heating equipment. Moreover, he has made statements that imply that Passivhaus buildings don't need heating systems. In fact, every Passivhaus building in the U.S. includes a heating system.

    These observations are mine, but (as my article notes) the PHIUS committee expressed similar observations. The report states, “In North America, ‘tunneling through the cost barrier’ was not achieved. Unlike Germany, there is not such a clear breakpoint where an expensive baseline boiler and hydronic distribution system (the typical heating system in Europe) can be eliminated for great savings.”

  14. Antonio Oliver | | #14

    Tunneling and Cost
    I wonder if you might comment on how much of the "tunneling through the cost barrier" is attributable to the differences in soft and hard costs for the U.S. and E.U. Oftentimes it seems that the cost structures for many aspects of home building are vastly different. For example, it boggles my mind to hear posters like Alexi Arango report that his PH Euro windows were imported for less money than none-PH offerings of well regarded American brands. Thoughts?

  15. User avater GBA Editor
    Martin Holladay | | #15

    Response to Antonio Oliver
    Of course the very high cost of hydronic heating systems in Germany -- perhaps the most expensive residential heating systems in the world -- affects the idea of "tunneling through the cost barrier."

    I have no doubt that when a German Passivhaus designer reduces the design heating load to the point that the hydronic heating system can be replaced with a less expensive heating system (often an air-source heat pump or electric resistance heat distributed by ductwork), significant HVAC equipment savings are possible.

    In the U.S., there are many possible ways to design a heating system. Often, designers make mistakes. Sometimes, American architects or engineers specify a $40,000 ground-source heat pump -- so if a Passivhaus designer can convince the engineer that this specification is stupid, of course savings can be made.

    However, in a broad area of the U.S., a standard heating and cooling system consists of a split-system air-source heat pump connected to forced-air ductwork. When the return-air plenum is connected to a central-fan-integrated supply ventilation system (simple and cheap), this approach provides heating, cooling, and ventilation at an almost unbeatable price.

    Another inexpensive option is an exhaust-only ventilation system (that is, a Panasonic bath fan on a timer) and one ductless minisplit.This type of system can be installed in a Passivhaus -- although it rarely is, because Passivhaus designers almost always insist on installing an HRV -- but it is more often installed in a simple house that doesn't meet the Passivhaus standard.

    A conventional house can have a well-designed, inexpensive HVAC system, or it can have an extravagant, poorly designed system. While poorly designed HVAC systems for Passivhaus buildings are rarer, they certainly exist.

    To sum up, in the U.S., the average Passivhaus building does not have an HVAC system with a lower cost than a typical forced-air heating and cooling system with central-fan-integrated supply ventilation.

  16. Antonio Oliver | | #16

    Thanks, Martin
    Thanks for expanding. To make a final comment though, maybe I got the wrong take-away, but I was persuaded by an article recently (maybe here on GBA) that it's too easy to bungle ventilation integration into your central A/C ducts. The inference from me was that perhaps one is better off paying the extra money to keep it separate regardless of how energy efficient the house is. H, V, and A/C instead of HVAC seems to come to mind for some reason also, not that most people could afford to separate all three.

  17. Dan Kolbert | | #17

    Don't know whether to laugh or cry
    Can't wait to read KK's response.

    On a related note, as I've told you privately, Eric Werling of DOE recently presented up here in Maine - I was impressed by their Net Zero Ready program. He and Sam Rashkin went over from EPA, where they worked on Energy Star, and set up this more encompassing and ambitious rating system. I think it may be the Pretty Good House.

  18. Malcolm Taylor | | #18

    Reply to Dan Kolbert
    That's good news! Any chance someone could do a blog on what their programme entails?

  19. Dan Kolbert | | #19

    Zero Energy Ready Home
    I believe Martin is on it. They have a good website as well.

  20. Malcolm Taylor | | #20

    And again...
    Thanks Dan

  21. User avater GBA Editor
    Martin Holladay | | #21

    Response to Antonio Oliver (Comment #16)
    You wrote, "I was persuaded by an article recently (maybe here on GBA) that it's too easy to bungle ventilation integration into your central A/C ducts. The inference from me was that perhaps one is better off paying the extra money to keep it separate."

    I agree that separate ventilation ducts are a good idea. They aren't required by code, and many homes without separate ventilation ducts work just fine, but the best possible ventilation system (at least in a cold climate) includes an HRV with dedicated ductwork.

    That said, I would never say that installing the best possible ventilation system "tunnels through the cost barrier" and results in savings. The fact is, most above-code measures (including a good mechanical ventilation system) cost more than the systems installed in code-minimum houses. There is no shame in that. If we want to build high-performance homes, we probably need to explain to home buyers why the added costs are worth it.

  22. User avater
    Ken Levenson | | #22

    A response regarding airtightness
    We've written a blog post regarding the airtightness aspects of the report called "BSC & PHIUS Passive Building Report Not Airtight" with references and links back to your post here. I hope it is useful to the conversation.
    - Ken

  23. User avater GBA Editor
    Martin Holladay | | #23

    Response to Ken Levenson
    Thanks for the link to your blog.

    To clarify my position: I am not arguing in favor of PHIUS's proposal for changing the airtightness limit for Passivhaus buildings. Rather, I am questioning Wolfgang Feist's explanation for the airtightness limit.

    Your position -- that it makes sense to aim for an airtightness target that can reasonably be achieved -- is defensible, and makes more sense than arguing that 0.6 ach50 is necessary to avoid moisture problems, mold, and rot.

  24. User avater
    Ken Levenson | | #24

    Response to Martin
    Hi Martin,
    Yes, understood regarding your position. I just think that PHI's position has more to do with buildability. - that if PHI thought .2ACH was reasonable they'd argue that .2 was necessary to avoid mold/rot... And like the earlier "eliminating a heating system" miscommunications, it appears to be more a matter of being lost in translation.
    - Ken

  25. User avater GBA Editor
    Martin Holladay | | #25

    Response to Ken Levenson
    Wolfgang Fiest has often repeated his idea that 0.6 ach50 is necessary to avoid condensation problems. Although many Americans insist that these statements are "a matter of being lost in translation," I disagree. Feist's command of English is pretty good, and when I have asked Feist follow-up questions attempting to clarify the issue, he has stuck to his guns.

    Here's what he said in one of my interviews with him:

    Feist: "If you have air flow through the structure, humid air flowing through the construction, you can get condensation. That is the most important reason it has to be airtight, to avoid problems due to structural damage from moisture. The structural damage problem is the reason why the airtightness requirement is a separate number. That was one of the experiences in very early superinsulated houses — there were often problems, structural problems, from condensation."

    [Dr. Feist turns to me and asks me for confirmation. I agree.]

    MH: "But it is still possible to have condensation problems in a building that is perfectly airtight. That’s what happened in Juneau, Alaska. Convective loops brought warm, humid air in contact with cold sheathing, and there was rot — even when there was no exfiltration."

    Dr. Feist: "It is always a good idea to have it as airtight as possible. From a technical point of view, having a figure of .6 ACH or its equivalent in metric units will give you a good guarantee that you don’t have damage from infiltration or exfiltration."
    __ _ _ __

    There are three issues here that Feist has muddled:

    1. There is no evidence that buildings with air leakage rates of 1.0 ach50 or 2.0 ach50 have problems with condensation.

    2. Problems with condensation can happen even when there is no exfiltration or infiltration.

    3. Some types of walls (for example, ICF walls) can tolerate lots of condensation without damage.

    In short, there is no basis for Feist's statement that 0.6 ach50 is necessary to prevent condensation.

  26. User avater
    Ken Levenson | | #26

    In response to Martin
    You're talking past each other..... The Germans talk about airtightness inboard of the insulation - so if you have airtightness in this way there can be no contact with cold surfaces and you are guaranteed no problems. Again, the the .6 it is a buildable limit they are positing. For renovation they make the limit 1.0ACH - the physics and risks are the same.... So to take both at face value there is an internal contradiction....unless there is something else going go as tight as you reasonably can be expected to. Then there is no contradiction etc, etc...

  27. Dan Kolbert | | #27

    So we should treat Feist's writing as less of a diktat and more as a zen koan?

  28. Jin Kazama | | #28

    Dr. Feist
    has manifested his hard position on different levels, many times now. This is one of the reason why PHIUS had to work on a modified standard.

    Why would dr. Feist change his position on airtightness ?

    I also disagree ( with my limited knowledge and intuition ) that this airtightness target indicates a condensation proof building, but, one has to admit that pushing for a specific, moderately severe 0.6ACH, obliges the designer/builder to do as best as they can to reach the target.

    In that, it seems to attain its goal, and we've seen many examples of teams surpassing this measure within acceptable efforts.

  29. User avater GBA Editor
    Martin Holladay | | #29

    Response to Ken Levenson (Comment #26)
    I think that the record clearly shows that both the Passivhaus Institut and PHIUS have taken the position that the purpose of the Passivhaus airtightness target is to limit condensation and mold.

    From a technical point of view, this position is difficult to defend, and for the life of me I have no idea why both organizations continue to try to defend it.

    It would seem to me that a much more defensible position would be that very tight buildings perform better and save energy compared to leaky buildings, and to establish an airtightness target that can reasonably (and cost-effectively) be achieved on a job site.

  30. User avater GBA Editor
    Martin Holladay | | #30

    Response to Dan Kolbert (Comment #27)
    Not quite. The Zen approach is more useful for interpreting the Pretty Good House concept.

    "What is the sound of a house with more cfm of exfiltrating air than infiltrating air?"

    You guys in Maine have all winter to come up with a few more such koans.

  31. Dan Kolbert | | #31

    We'll work on it
    We're meeting tonight. Maybe guided meditations.

    "Inhale and think of your make up air. Exhale and think about your mechanical ventilation."

  32. User avater
    Ken Levenson | | #32

    Response to Martin
    Not sure why you're repeating yourself - at risk of doing same: Yes, extreme airtightness is driven by "First, do no harm" principle. And yes, PHI has declared .6ach for new construction AND 1.0ach for retrofits - reasonable and cost effective. We think that is the case, while others may disagree. (I think this is all pretty well spelled out in our blog post.)

  33. Aj Builder, Upstate NY Zone 6a | | #33

    Dogs... look at all the
    Dogs... look at all the shapes and sizes and... cats... domestic anyway.... color changes...that's about it. Raining cats and dogs... PH... PHIUS........ and .... pee you, comes to mind.... now give me a PGH and I get pretty darn excited..... gotta go pee now... you know the puppy... that can't hold it...upon greeting the love of it's life. PGH.... for me.

    Sorry, just have a hard time explaining myself in peer review format and word. Too boring for such a short life on this planet.




    Start the nationwide cheer

    Who's on the plaque committee for PGH? If we can have one person per committee with full dictatorial rights, I'm in.

  34. Anders Lewendal | | #34

    opportunity cost/PHIUS
    Martin: Excellent article. I think you nailed it on all accounts. I hope the PHIUS staff and supporters take seriously your recommendation at the very end of the article:

    For the net-zero-energy designer, an envelope measure makes sense if the value of the energy saved by the measure exceeds the value of the energy saved by a PV system that costs as much as the envelope measure under consideration.

    All energy performance improvements should be guided by this measure. Although I believe the current PHIUS protocol goes well beyond the cost optimum point I am building a new custom PHIUS based home in Zone 6. I'll let you know how the costs compare to the annual savings in a year or so.

  35. User avater GBA Editor
    Martin Holladay | | #35

    Response to Anders Lewendal
    Thanks for your comments.

    If you want to write a guest blog for GBA in about a year, sharing your experience building a home to the PHIUS standard, we'd be interested in publishing it. Keep track of your costs, and keep track of your energy use and budget.

  36. Anders Lewendal | | #36

    response to Martin
    Thanks. I plan to keep track of actual costs compared to achieving an Energy Star Home which is our basic level. Since my client is not bringing in natural gas to the house we will install PV to achieve net zero. Should be easy to get actual energy use for a full year. I am happy to share my spreadsheet when we are done.

  37. Malcolm Taylor | | #37

    Looking forward to reading about it.

  38. Michael Keesee | | #38

    Passivhaus Controversy
    Martin once again brings clarity to the Passivhaus controversy. In particular, his comments on whether the market will accept Passivhaus, even the new "American" definition of Passivhaus, is the most important question to ask. Here's my take on Passivhaus. I spent 22 years trying to persuade national production (and local custom) home builders to build energy efficient homes and adopt new business practices as the manager of a utility new construction program. In brief, it wasn't easy and most builders resisted incorporating energy efficiency into their new home products (and still do). Without changes to California's Title-24 building code, I doubt that my efforts which included providing generous cash incentives and free training would've gone nearly as far as they have. And as far as Title-24 has come, it is still far short of Passivhaus, German or American.

    The problem I had (and have) with Passivhaus was that it represented an ideal "standard" that as Martin explains does not recognize market conditions and more importantly the American home building business culture. As an ideal standard, I appreciate Passivhaus for setting the bar for what can be achieved, especially from a research point of view. But that's where Passivhaus falls short. As an unattainable standard for the overwhelming majority of home builders (and incomprehensible standard for home owners), it will have little or no influence on how homes are built. This important fact is especially relevant for areas without stringent building codes, which is the majority of the country. Getting bog down on definitions is something of a pointless exercise if the intended audiences - home builders and owners - ignore it.

    The most pressing home building issue that needs urgent attention is radically transforming the home building industry's culture and building practices, not coming up with a new foreign, obtuse, difficult to implement, costly standard. In my experience, the one thing that caught the attention of both builders and owners was the Zero Energy Home (ZEH), and by zero energy I mean it's simplest, easiest definition- a home (building) that uses as much energy as it produces (or a zero, annual utility bill for homeowners). Both builders and owners instantly grasped what ZEH meant and were enthusiastic about it. The problem was in building a ZEH, and so long as builders continue their current practice of basing their business on out dated building techniques, such as in field assembly, and low-cost subcontractors ZEH was hardly cost-effective, especially from a low cost production business model. The advent of low cost PV is something of a game changer but still represents what I'd call an "old school" approach to improving home performance; that is, a "technological" solution - let's just slap on a new (costly) "technology" on to improve the home's performance rather than use design and improved business practices to gain efficiencies.

    This business approach to ZEH can be seen in the best of the Japanese production home builders, like Sekisui House. Sekisui and others are true production home builders that employ continuous quality improvement in the manufacture of homes, controlling all aspects of home building. Sekisui and others have been building ZEHs for several years for arguably the most discerning consumer in the world, the Japanese home owner, and they offer many lessons on how home building can be improved in the USA. I believe that the key, therefore, to wide scale adoption of ZEH is changing builder business models to a practice that builds homes utilizing continuous quality improvement techniques.

    But more importantly, wide scale, rapid adoption of ZEH is critical if we want to dramatically reduce the energy use and its environmental impacts of the residential sector, particularly contributions to greeenhouse gas emissions. As Martin points out, Passivhaus still requires energy to operate. And, the market will never accept Passivhaus as a building standard.

    To sum up then, Passivhaus, American or German, represents in my mind an important research standard that demonstrates the technological limits of home performance. It's not a standard that will work in the America home building market or appeal to home owners. ZEH is a building concept with wide spread appeal to both home builders and owners with tremendous potential for lower residential energy use and its associated environmental impacts, although poorly implemented in the USA. ZEH is best achieved by home builders who employ state-of-the-art technologies and use modern continuous quality improvement techniques to advance design and lower costs. It's critical that we devote our limited resources on assisting the home building industry change how it builds houses, but deploying another standard, one that's confusing and almost impossible to achieve is not the best way to make this change.

  39. Alex A | | #39

    The purpose of a "passive house" standard
    Thank you to Martin and all the commenters here. I haven't read the whole draft report but I hope to get to it.

    In a world of proliferating green building standards, I think "Passive House" should claim relevance by being a restrictive standard that focuses almost exclusively on building envelope. To me a "passive (passiv) house" should be a house with the best "reasonable" envelope. It may also be net-zero, LEED Platinum, Energy Star, HERS 50, etc, but isn't necessarily any of those things. It probably has to go beyond the "pretty good house" measures. In places with really cheap electricity (green or not) it should probably be uneconomical.

    I'm basing this on an understanding of envelope performance that might be flawed, however. I'm assuming that at some point, additional thermal control stops making sense at any energy price, and that point isn't too far from what the current passive house standards demand. At a certain point the embodied energy of the insulation (and/or the structure that supports it) exceeds the energy it can save in heating and cooling. At some point air sealing hits diminishing technical returns. If the "leak" you're hunting down during construction will spill less conditioned air over several years than a slightly damaged window gasket, or a door left open to get the groceries in, is it not a waste of effort?

    I don't have numbers to back this up (RTFR! I hear you scream), but I'm assuming at some level of thermal performance, the 15 year energy use of a house starts to get extremely sensitive to assumptions in the modelling program. I don't know how close a top of the line passive house is to that point, but if the descriptions of some European examples are honest, we must be getting close.

    Just my thoughts for now. If I had to sum up in a sentence, I'd say PHIUS should avoid being too pragmatic, I think there's a place for a cutting edge standard.

  40. Aj Builder, Upstate NY Zone 6a | | #40

    Michael Keesee you have the
    Michael Keesee you have the best post I have seen in a long time.

    Net zero could be a one sentence energy code. It could be easily mandated by selling someone net zero electricity for a set price and if you go over you pay ten times as much or what ever the environmental people say the real value including pollution that energy should cost.

    And let the free market the builders you refer to figure out how to get there and how to learn to do as your Japanese have started to do.

    One simple rule and the free market. That's how the X Prize works so well. Put out the challenge and let games begin. That excites me as a builder. And so I fully agree with you. I just don't want to see another 800 pages added to the code books, so there I also fully disagree with you if that is what you think is missing as you implied by saying much of the country is lacking strong codes and strong enforcement.

    Make a meter that has your set allowance programmed in. Make an inside panel and smart phone app to keep the owners informed. And let the owners decide how to get to stay net zero or pay to play outside the rules automatically. No need to write a book of new regs and no inspectors and no payroll and administration and retirement and health care... I see this costing billions if tree huggers or school teachers implement this or dollars if it were my program or a builder were in charge.

    And even more important, when oil is down like now and the economy is decent, rules can jump up.

    And twice as important. Set up a timeline that every year via your homes age,it has to comply so that all existing homes are "net zero metered" (the name of the new aj plan) by 2035. 5% of the oldest homes go net zero annually. start with homes built from the years 0-1600, then 1600-1650.... analyze the home, set the new meter, and in one year it turns on the new netzero allocation program and you're on your own. Apply for energy stamps to a pool of private donators for material, money and labor via a net zero kickstarter restartingnetzero site.

    You all are smarter than me.... take my lead with this post and make something happen. Make is simple. Use the free market ideas. Keep the code pages down! I think one line is enough. That is my X prize challenge.

  41. User avater
    Bronwyn Barry | | #41

    Michael Keesee
    I think your point regarding the need to transform our building industry is well taken and where most of us agree. How we affect that transformation is where we lack consensus. Despite your misgivings about Passivhaus/Passive House (and respectfully a number of totally erroneous statements regarding the standard) I believe that Passive House provides both the tools and the methodology that our industry so sorely needs to both transform itself and simultaneously reach the mythical 'NZE' goal many aspire to, but have no idea how to get there. (In as much as that is possible for what I'm guessing is around 1/3 of our built environment.)

    I'll respond to you more comprehensively off-line, since it looks like this thread is almost dead. I'd like to share a growing data set of Passive House projects in California that I think may surprise you, or at least make you reconsider your viewpoint. I've also just started four new projects this year, all driven by clients requesting Passive House (or at least an approximation, which I'm now calling 'Progressive House.') It's an exciting time to be working in this field and even more interesting to be focused on what you rightly refer to as 'a cutting edge standard.'

  42. User avater GBA Editor
    Martin Holladay | | #42

    Response to Bronwyn Barry
    Thanks very much for your comments. I can assure you, this thread is not "almost dead." (It's solar thermal that is almost dead -- not online communication.) The conversation here is only dead when readers like you decide to take the conversation off-line.

    If you are willing to share aspects of the Michael Keesee / Bronwyn Barry dialog by posting your comments here, all GBA readers would be grateful. Thanks.

  43. Tom Bassett-Dilley | | #43

    zeroing in
    I think PHIUS and NZERH are heading the same direction and will eventually converge: it makes sense to invest as much as is reasonable in passive measures (insulation, airtightness, passive solar) so that you can use a cost-optimum amount of PV to get to zero. To that extent, you prioritize Passive, or better said, you figure that amount out first, then figure out your PV.

    So how are you going to figure out that "reasonable passive measures?" Rule of thumb? IECC? Now imagine you're going to try to tell the US/Canada--from Key West through Edmonton to Fairbanks--what is the definition of "reasonable" for passive measures...kind of a lot to figure out there. I don't think many people are going to run out and get BeOpt and spend hours finding the cost-optimum, but that was what PHIUS did, using over 100 climate data sets, though they took it just beyond optimum--I think it's like a future-proofing idea, since energy rates will increase. Perfect? No. Helpful? Yeah, very.

    Having built a PHIUS+ certified house and designed a few others, including a few to the proposed adapted standard, I can say that the proposed standard is definitely easier to reach, closer to IECC, and, in the world of high-quality custom residences, not that big a deal if a good designer and builder are involved. It won't be for production builders or those who don't want to mess around with modeling, and if those wind up Pretty Good, that's not bad. Even better if they are NZER--but they should check to see if they can get to NZ using their rooftops for PV in extreme climates.

  44. Fiona McKenzie | | #44

    Passive House standard and non European countries (Superpod)
    Fascinating thank you! I have been wondering about the PHI/PHIUS split details. From the perspective of another non-European country (Australia) the challenges of the PH Standard are many. 99% of the design and building industry has not heard of ... repeat. ... never heard of ... the PH Standard.

    I built a certified passive house and learnt what this means in all its glory.

    Barriers include lack of components, lack of services, lack of understanding, Oh yes, and that means cost. I agree that for area where elec is cheap AND would add where the climate is mild, AND in a country that has a handful of passive houses, if any, PH can seem prohibitive.

    But it is only cost prohibitive if your only equation is cost of building envelope vs cost of power.

    I think we need to raise the other features and benefits of PH more. And make it easier to construct. And think of other ways of compromising without compromising.

    I therefore made my building system a replicable building product to the PH Standard, with new connection details etc. (company Superpod, website

    Very very easy to build, and fast. Anyone can do it with a little training.

    So adding speed to PH benefits helps. That can make it a cost saving if you have larger projects including high rise.

    And it has low maintenance components that don't need painting. Ongoing maintenance costs are reduced.

    It is steel therefore robust.

    The comfort benefits of complying with PH Standard are blowing us all away. Everyone who walks in the door wants one. In a climate (Melbourne Australia) where temperatures bounce around even in a day between 38 and 10 degrees, who wouldn't want consistent relaxing fresh but stable temperature air inside? The effect on the psyche is truly remarkable. Put a dollar value on that!

    Barriers to entry for PH include an obsession with windows here, which means imported windows, because triple glazed high qual windows virtually don't exist here. people also like fireplaces or wood stoves.

    Finally, I have decided that to offer the product to those who can't afford a whole PH, we will have a PH core, with a sunroom annex - the annex will be usable for comfortable days, or when you want a wood fire stove. It can have single glazing and be cheap and poor insulation etc. Could even be just corrugated iron!

    That is compromise without compromise.

    One more thing, I would like to see PHS adopted and adapted around the world without country-specific variable standards. It is hard enough without people trying new measuring methods. I say let's stick to one method but find other creative solutions to cost barriers and expand the debate about PH benefits.

    (oh yeah, like that other little benefit, climate change improvements from reduced carbon emissions... but who in the building industry, government or customer base really cares about that?)

    Our building system can be done anywhere as the products are readily available (apart from windows!). This is my attempt to promulgate the established standard for low energy use in building design across country borders.

  45. User avater GBA Editor
    Martin Holladay | | #45

    Response to Fiona McKenzie
    Your comments imply that most builders in Melbourne can't build a house with even indoor temperatures. That's surprising.

    You wrote, "Who wouldn't want consistent relaxing fresh but stable temperature air inside?" I agree that stable indoor temperatures are usually desired. But they aren't that hard to achieve.

    A good builder should be able to deliver that. What you need is a fairly airtight envelope with decent insulation, and a well-designed HVAC system. You certainly don't need a Passivhaus to achieve that -- although I don't doubt that a well-designed Passivhaus can provide it.

Log in or create an account to post a comment.


Recent Questions and Replies

  • |
  • |
  • |
  • |