15kWh is dead. Long live 15kWh.

Hi Everybody:

Welcome to my brand new blog! I hope to keep you updated on the progress of Passive House and PHIUS, and to spark constructive discussion along the way.

On that note, I’d like to start this blog by addressing what we at PHIUS think will be the central issue for Passive House in 2012: fine-tuning the Passive House standard’s certification criteria, which were developed for the central European climate and market, to the unique climate and market needs of the United States and Canada.

Having evaluated five years of data from PHIUS’ portfolio — including more than 100 reviewed and/or certified projects of varied building types in the United States and Canada (thanks to the good work of the Passive House community) — we came to the conclusion 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/m2yr or 4.75 kBTU/ft2yr for the North American continent’s more extreme climates.
  • Define what has been missing all together so far – a stringent requirement for the third load which is the significant energy consumed in North America for dehumidification.

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 to Passive House groups from other countries, like the Swedes. From our perspective, we do not feel that this adaptation guts the value of Passive House.  Instead, the goal is to introduce a new balancing act into the standard.

On the one hand, we need to let go of the illusion that there is a god-given magical number that can cost-effectively be adhered

Average solar radiation exposure is just one factor that differs dramatically between Germany and the US. (National Renewable Energy Laboratory, European Commission)

to worldwide. (The notion behind “15 is dead.”) In North America, in some DOE designated climate zones (specifically, top 5 and up and bottom 3 and down), the cost of meeting the mark is problematic. The added expense required to hit 15 is not recoverable over the life of the building.

On the other, we need to maintain the value of having a single baseline. (“Long live 15.”) The first 100 projects or so have indeed validated this benchmark as an appropriate design starting point for excellence in high performance building in North American climates.  The baseline builds into the standard a necessary rigor and elegance that gives the brand its strength.

The PHIUS Proposal

PHIUS is proposing to the PHIUS Tech Committee — composed of industry and policy leaders from the United States and Canada — to leverage the PHIUS dataset of 100 buildings, and to solicit feedback from the consultant community to create a new protocol that will allow Passive House professionals to determine practical modifiers to the standard to address climate, small home and retrofit scenarios. This new protocol would be used to determine the acceptable modification ranges for:

  1. Additional peak load allowances (heat, cooling, latent) per climate other than the cool moderate reference climate.
  2. Annual space conditioning requirements (heating, cooling and dehumidification) that follow from acceptable higher peak loads per climate other than the cool moderate reference climate.
  3. Annual source energy requirements. Based on the new annual requirements per climate other than the cool moderate reference climate.
  4. Airtightness criteria that will have to be re-evaluated based on climate; hygrothermal criteria might have to be added as well.

By introducing this protocol into the standard process, we start with the baseline design of 15kWh for a climate dominant space conditioning need (might be heating or cooling or dehumidification). It is business as usual from here. If you meet the governing energy metric in a cost effective way you are done. Congratulations!

If you find yourself in a climate that is more extreme, you will need to benchmark the economic benefit expectations. Using the new protocol, the level of insulation can then be fine-tuned within a small range of above or below the energy metric of 15kWh without sacrificing the quality and comfort criteria. Tuning down the conservation level in return fine-tunes the annual energy requirement specific to each project without having to resort to prescriptive measures, possibly wasting savings potential.

In this manner a new Passive House balancing act is achieved – 15kWh remains the only fixed criteria, while deviations to both sides are allowable within clearly defined parameters.

We envision this to be a simple evaluation process to determine cost-effectiveness that will not add significantly to the consultant’s workload or complexity of the design tasks. The recently announced PHIUS+ certification program — that introduces a level of quality assurance into the Passive House standard — can also be used to assure that all building science and quality criteria are upheld regarding this new protocol.

From Movement to Mainstream

Addressing the issue of modifications is a pivotal moment for high performance building in North America! Its time has come because we now have the dataset necessary to make these adjustments. PHIUS Tech Committee evaluation of over 100 projects represents the first study of an unprecedented volume of data on implemented Passive Houses in North America.

It’s also a pivotal moment because we are proposing a departure from a single one-size fits all international standard. We welcome everybody who would like to contribute to this effort.

This proposed shift of course will not happen overnight. There is a lot of work to be done.  It will be a careful, collaborative process driven by the experience and data gathered from real-world experience. I’ll be providing updates here, and PHIUS will provide updates via its e-newsletter and Web site in the next several months.

This progress is very exciting to me! I have been waiting for this for a while. We are finally tackling the contradictions that we all have been struggling with and it seems we are about to solve them.  In the process, I look forward to your comments and input — I hope you’ll use the comments feature (just click on the little bubble below) to weigh in!



52 thoughts on “15kWh is dead. Long live 15kWh.

  1. The baseline builds into the standard a necessary rigor and elegance that gives the brand its strength.

    Sounds like you are saying PH is both a standard and a brand… which is it? I hope it is the former.

  2. Let me be among the first to congratulate you:

    CONGRATULATIONS, KAT for continuing to be bold in your efforts to advance the frontiers of building science and the dissemination of that science through your tireless work with the Passive House Institute, US. I look forward to what I am sure is going to be an exciting effort and a vigorous discussion!

    I must admit, though, if I had known that you had enough spare time to write a blog I would have been bugging you with a few more questions about the projects I am currently working on!

  3. Thank you, Kat, I welcome this.

    I suggest that adding in economic benefit calculations is not a good direction – here’s reasons why:
    – it presumes we have some idea of the cost of energy over time into the future
    – the cost of energy is vastly different across the US – I just returned from IL where attendees of my workshop told me that natural gas costs them well under $1/therm and electricity can be had at time-of-day rates that drops off-peak rates well below $0.05/kWh.

    I have produced a draft amendment for housing in my climate region (northeast of NYC). Its principal features:
    – Primary energy is most important, and the limit is per bedroom not per sf – this begins movement to resource equity and limiting impact per person rather than based on house size. This is the largest proposed change.
    – AHD is proportional to HDDs.
    – DHW usage baseline is increased to 10 gpd/person
    – Electrical usage for lights, appliances and plug loads is increased as houses are larger than the PH baseline of 377 sf/occupant.
    – PE factor must be increased over PH value of 2.7 for the US, probably at least 3.4.
    – Site-generated renewable electricity can be used to offset primary energy using the PH 0.7 PE factor, up to 1 kW (DC rating) per occupant, where # of occupants is # of bedrooms plus one.

    I will post my proposed amendment on my blog if there is interest. It’s been out for review to a small group in the Northeast for a few weeks.

    • Marc, thank you for sharing your vision on this, I know you have been working on this for a while. This is terrific, lots of good work already underway. Hope you will be sharing your experience, progress and data from your approach in the NE as well when you start implementing it.

      I agree with all the specific points you are listing here. Still like to investigate, and I have some ideas, how to get the economic feasibility into the fold.

      I am totally with you on the importance of source energy that is currently not yet appropriately reflected.

      I think it would be great if you shared your proposal on your blog!


    • I agree with a number of these points, Marc – and would love to see your extended proposal.

      It is true, the EU source factor is much ‘greener’ than the US. We use significantly more energy than the average European. Our DHW consumption is also higher. I’ve had this discussion with a number of mechanical engineers here in the NW – including data from built PHs.

      That being said, I don’t think we should change the (universal) standard to conform with our poor standards of consumption. We need a fundamental shift in the way we live (e.g. to achieve 2000 Watt Gesellschaft). We should be striving to be as efficient in our consumption as Europeans – and no, this does not mean you have to give up daily showers! Changing the standard to reflect how Americans want to live, as opposed to how they should be living, seems a poor direction.

      However, the kWh/no. of bedrooms is hard for me to agree with for PH – there too many variables, plus it isn’t a ‘universal’ (e.g. doesn’t work for non-residential). I could also see this being gamed rather easily. Additionally, there already is a ‘per person’ impact built into PHPP on the energy usage & DHW fronts.

      If it’s too difficult or not cost effective to achieve PH on single family houses in environments like Yellowknife – maybe we need a fundamental shift in our lifestyles. Maybe we need to ask hard questions or make hard choices, like whether it actually makes sense building single family houses in the middle of the frozen tundra. Besides, there already are a number of less strict energy standards that can be utilized for these ‘extremes’ rather than changing the purity that makes Passivhaus so fundamentally attractive. Minergie, Niedrigenergiehaus, LEED, Built Green to name a few.

      As consultants, we already have a Passivhaus retrofit standard we can use that deals with cost effectiveness and difficulties of remodels – EnerPHit. Lastly, I completely agree with Hayden (and a number of other PH folks) that if we’re going to change the standard, we need to re-name/re-brand it.

      • I also believe that PassivHaus standard, is and should remain, what it is:

        A standard which represents a defined energy demand per dwelling.

        I also believe that no one needs a house >1400 sqft for a family dwelling, and anyone who can afford such a monster, can afford the engineering necessary to bring that monster into conformity with PH standard, should they so wish.

        It is my understanding that R-15 windows are now available, which should help matters.


    • We all know that $1/therm of natural gas does not account for the cost of decontaminating the ground water we are going to face once the fracking industry gets its way.
      $0.05/kWh of electricity does not take either into account the cost to the environment that the CO2 is causing by thermoelectric.
      We must stop kidding our self with the idea of “cheap energy” while pushing the balance of the actual cost to our future generations, a cost that is going to be a lot more difficult to recover than the extra insulation cost of a building.
      I agree with Mike Eliason statement that we need a fundamental shift in the way we live.
      Before relaxing the standard we should tabulate the data that is being generated from PH projects to reassure the validity of the standard. There is already a house in Main with 7500 HDD that meets PH standards at a construction cost of $130/sqft
      While Detroit arrogantly kept producing gasoline hogs, the Japanese and Germans left us behind and we got a reality check in the auto industry. We are seeing the same in the building industry because our reliance on “cheap energy” and lifestyle. We have a moral and professional responsibility to get to the highest energy standard.

  4. Pingback: 15kWh is said to be dead/alive. « Rocky Mountain Passive House

  5. I am glad to see this issue coming forward in a deliberative and thoughtful manner.
    I look forward to seeing more details and discussion.

  6. Katrin,

    Could you clarify the larger context of your focus on adding flexibility to the heating consumption limit (15 kWh / m2 yr or 4.75 kBTU / ft2 yr) in different NA climates than the central European that PH was founded on?

    Is your thinking that Passive House as codified by PHIUS should retain the hard cap of 120 kWh / m2 yr or 38 kBTU / ft2 yr of total Primary Energy Demand, but allow more flexibility in the sub-componants of the standard as Marc is describing above?

    Or are there also conversation going on about allowing modification to Primary Energy Demand as well?

    At the PHIUS 2011 Conference keynote Marc specifically pointed to a need for increased focus on domestic hot water energy use in very cold climates, that having Space Heating Demand sitting there as the top XLS cell in PHPP is distracting from the most important PH limit: Specific Primary Energy Demand.

    This is certainly understandable, the climate doesn’t care how much heating energy each North American uses per SF of house we own, all our atmosphere cares about is total damage we do.

    The fact that the Passivhaus / Passive House standard doesn’t give people who live in cold climates (like myself) license to do more climate damage has always been of huge importance. Too many other programs cut too much slack just because people choose to live in more difficult climate zones.

    Jesse Thompson
    Kaplan Thompson Architects

  7. I believe this is a very positive step for the Passive House movement in North America and beyond, as well as for developing cost-effective high-performance homes, in general.

    We currently use the existing Passive House standard as our baseline level of energy efficiency before adding active solar and/or other renewable systems to achieve Net-Zero-Energy and/or Carbon-Neutral homes.

    However, during our initial studies in support of USEI’s National Net-Zero-Energy Demonstration Program (www.usei.org), we often found that when cost-optimizing for Net-Zero-Energy or Carbon Neutrality, the lowest total cost often occurs by departing from Passive House standard’s 15 kWh per square meter.

    Accordingly, greater flexibly in PH specific heating / cooling energy would be very helpful (as long as it does not dilute the strength of the standard.)

    Further, I believe PH should not necessarily have separate heating and cooling limits of 15kWh each, but instead should utilize a “Total Specific Space Conditioning Energy” that includes heating, cooling and humidification/dehumidification. This approach leads directly to better overall cost optimization.

    As always, happy to assist. Cheers.

  8. Kat,

    As someone currently engaged in the design process of a small passive house in an extreme climate (Colorado Rockies, Zone 7), I am hitting the “central European climate baseline” wall. I have no cooling load, but am limited to the 4.75 heating threshold regardless. I would LOVE to see an energy consumption threshold that takes cooling and heating into account. I will continue to pursue PH certification under the current standards. In doing so, I believe ultimately the project will surpass PH standards because of the lack of cooling energy req’d. As said elsewhere and likely more eloquently, the cost to hit the current standards is up there. I am being “penalized” for size, (650 sq ft) urban infill project (a good thing as opposed to sprawl), and I am being “penalized” by my climate (8000+HDD). I applaud the efforts for climate specific PH standards, as it would make what I am doing more plausible to the average client, and probably myself. Nevertheless, a small part of me feels there is room for innovation (systems, products, etc) to make buildings in all climates hit the existing central european standard. Perhaps there should be a certification “level” for building that hit the existing standard regardless of size, location, etc. I hate to use the word “platinum”, but….

    My 2 cents.

    Thank you for your efforts, Kat, I am fully in support of these efforts.

    Erik Lobeck

  9. If there is to be some loosening of the standard I would allow a greater range in the comfort zone. If you live somewhere that is 100F and 90% humidity, 80F and 50% humidity may be very comfortable. Likewise in cold climates an interior temperature of 60F may allow for comfort and energy savings. The rigid temperature zone should not be out of the discussion.

  10. I would also like to see the issue of a secondary energy source revisited. At present, I am unable to get my house certified because I use electricity for space heating and hot water. My only other energy source is propane for cooking. My passive house consultant tells me that I could become certified if I tore out the electrical hot water heater and installed a gas heater or installed a solar hot water system. I do have a photovoltaic system that first serves the needs of the house before dumping the rest in the grid. I’m told that I can’t use the portion that directly serves the house as a secondary energy source even though it is separately metered. This policy doesn’t make sense to me.

  11. All really well taken comments. Thank you all! It is good to see that there is a very positive notion out there on this topic and quite a few real time experiences got contributed by John and Erik, that indeed confirm the opportunity here to rethink.

    Jesse was asking for clarification on the larger context of focusing on allowing flexibility to the annual conditioning demands.

    The 15 kWh/sqm yr annual space conditioning demand is really a proxy for peak load requirement. Reducing the peak load all the way to down 1 W/sqft or 10 W/sqm in the cool moderate climate results in 15 kWh/sqm yr. Because the annual heat demand is less abstract than 1 W/sqft and it is easier for people to grasp, the focus shifted from the peak load criterion to the annual number. It is still just a result of the peak load expectation. The peak load criterion is the constant, everything else follows.

    I suspect that there is a similar more relaxed peak load threshold that still is economically possible to be delivered through slightly increased low flow ventilation air (additional fan and small recirc), which would then result in a specific slightly higher annual demand. How far can the comfort criteria be relaxed without compromising what we expect in a Passive House?

  12. Kat,

    Thank you for providing further insight into the the underlying mechanism behind annual heat demand. I appreciate Alex’s comment with regard to relative comfort. To expand on that with regards to our discussion, (I am probably missing some deeper underlying PHPP concept), but what if “underheated” days were tolerated to a certain percentage similar to “overheated” days? This could help lower the amplitude of worst case swings in the winter with regard to BTU’s required in a worst case. If 10% of days can go over 77 deg, shouldn’t it follow somewhat logically that on some TBD percentage of days the interior temp can dip to 64 instead of 68? To what degree this may help I don’t know, but thought I would add that to my earlier comment.


  13. I think Passive House is great. But it’s nothing to me. It’s technology. Not religion. Not politics. Give me a calculator and I’ll set aside my slide rule. Give me a computer and I’ll give the calculator to Good Will. Like any technology, Passive House must evolve to stay relevant. And, one day, a more powerful technology will develop, and Passive House will be set aside. I hope I am still practicing architecture when that happens.

    I applaud PHIUS for looking for better ideas. I trust that changes will be true improvements, based in science, and that the science will happen first – the changes following naturally from advances in understanding vetted through open, expert peer review. And I hope that what emerges will be rational, coherent, and internally consistent.

    On other dark days, I worry about a second definition of Passive House – diverging from the clear, internationally-agreed-upon one many have worked to establish in this country. Is there room for both? Wouldn’t creating a second one raise more dust in the wake of the already confusing break between PHIUS and the PHI? Wouldn’t that confusion dilute meaning and create room for more confusion? If there are two definitions for Passive House, why not a third? Why couldn’t anyone call anything a Passive House? No one says slide rule and means computer. Have mercy on all of us. If a new standard is created, give it a new word.

    • We all know that Minnesota is not Mississippi and that Atlanta is not Albuquerque, but the idea of changing/modifying/messing around with THE STANDARD is scary. I have often said, when making both public and private presentations, that the Passive House energy standard is not magic, but the results can seem magical.

      Having lived in a “Near Passive House” (not Certified) since November, 2008, I can say that it is the most comfortable house I have ever lived in while being the cheapest to operate – a magical combination when you think about it. Luckily for us it is science and not magic that produces that too-good-to-be-true result, because anyone who has ever read a fairy tale knows that it is dangerous to mispronounce a spell or change the ingredients of a potion.

      If Passive House were a fairy tale, another activity we would want the hero to avoid would be to blaze a trail where no one has been before. I will admit that I felt some apprehension when I first heard that the Technical Committee would consider changing the ingredients of THE STANDARD. I was somewhat relieved when I learned of the Swiss program Minergie-P, which is an adaptation of Passive House that has been in existence for about ten years now.

      I was more relieved when I realized that I had heard no reliable reports of any Swiss architects or builders turning into frogs or swans in the past few years! And just today I learned of the program “Passive-on” which was an effort to make Passive House fit the climate of southern Europe more effectively. All of which leads me to the conclusion that what PHIUS is undertaking is not unique and, maybe, we could all benefit from a little history lesson, or news report, on the evolution of Passive House and Passive House-like standards in other parts of the world.

      • Perhaps the problem is one of nomenclature. There seems to be agreement that southern Italy is not Minnesota. Throughout history, before the advent of cheap fossil fuel power, indigenous structures reflected their climate. IMHO the Passive house standard could follow suit. I agree it is important not to dilute the standard. What if instead of calling it something else entirely, it where simply called PHsouth, PHnorth, or PH4 or PH 7. Each subcategory number or name reflecting a region? Even better if they coordinated internationally. i.e “PH 6” applied to regions in Europe, Asia,and the US. They would all fall under the passive house umbrella. A passive house in International Falls Minnesota could be called a passive house even if a slightly different metric is applied due to region. A passive house in Seattle will be called a passive house for the same reason. Both would be comfortable and exude all the virtues a passive house should. One might require more cooling than the other, but both would meet a combined annual demand standard.

        In my position, if I want to continue designing passive houses based on a central european climate and do so affordably (one of the fundamental premises of the PH movement) then I have three choices.
        1_Move to a central European Climate
        2_Find “money is no object” clients
        3_Call it something similar to a Passive House, but since it doesn’t meet the standard because of climactic differences or size call it something like “Not quite but Close to a PH” -which could ultimately threaten the integrity of the Standard more than creating officially recognized climate dependent subcategories.

        another 2 cents and I’m all out of change.

  14. I agree with most critiques but don`t see a science based fix.

    I think if you make it economy based Marc hit it. Not enough science there and things could change quickly. Unless you come up with something like the 10W/m2 for each climate zone, where you insulate until you safe money somewhere else. If this is not the case it is going to be complicated to define/ justify any changes.

    If you make the criteria bedrooms instead size I bet that designers/ builders come up with pretty creative ideas for short term bedrooms…. .

    If you count PV offset you may as well count if a owner buys a wind turbine anywhere. Much more effective than PV and he could call any building a passive house. I still encourage people to add PV but it just doesn`t contribute to the buildings performance.

    I agree with the other suggestions of Marc because they don`t change the standard but rather reflect culture adjustments.

    I also agree with Hayden Robinson that if you come up with something “new” it should be called by a different name. Also I would be really careful of loosening up the standard as this would not be considered moving forward. And as you know the step from passive house to net zero is not big so naturally this is the next step…

    There is so much else to do like publishing “how to” protocols, Assembly and Detail catalogs etc.. ….

  15. One might also want to take into account what the Swedes either have done or are contemplating. The US is not alone.


    FEBY Kriteriejämförelse av Passivhus enligt PHI och FEBY

  16. Rather than allow for deviations around the 15 kWh/m2 number, or other rigid targets (even if somewhat arbitrary) I suggest altering the definitions and referenced standards for certain inputs, especially those that already have a definition in North America.

    Take the Treated Floor Area measurement. In North America we place a different emphasis on space usage and types. Make it more in line with accepted North American building measurement practices and standards for residential and commercial space. Some areas may go up, some may go down, but the science is still there.

    Likewise, the source penalty needs to be re-examined. Our electricity supply mix varies all over the place, from year to year, and from month to month. Keep the 120 number itself, but change the penalty for using electricity.

    Stop the arbitrary penalization of non-PHI-certified products, go on the basis of science for performance tests. Publish the calculation and testing standards and then allow third party labs to perform the tests, locally.

    All of these can be done without changing the science and the hard numbers we have come to know.

  17. A few thoughts to add to all good fun thinking going on here.

    Comfort zone: yes, this is one strategy/research that is being tackled by the tech committee. Extremely interesting. First, we have not defined what that comfort criteria is for a cooling climate. Initially one might think oh that’s easy but then it does not come that easy. And then if we relax R, what does that do to comfort? Where do we start to lose this superior warm fuzzy feeling in a PH? Lance seems to feel quite comfortable in his almost Passive House (Lance, love the image of swiss PH-frogs, made me giggle, and do share the relief).

    Secondly, yes, the next strategy we also thought about was what is proposed here: a similar to the 10 W/sm relaxed peak based on cost effectiveness of space delivery options. That works. Could be lots of fun to think about this one.

    Like the idea of PH4 and PH7…

    Got to love the Swedes, they stood up before everybody else and said “hey, this might not be the end of it all…”

    In regards to the impression that we are proposing a new standard, we don’t. Hence no need for renaming. The Germans did not feel that that was necessary either when they took it from the Canadians, they kept the name that the Canadians coined with the simple explanation: it is not a brand, it is a physics principle. We are proposing the same thing, refining the physics principle of Passive House. Still lots to discover here.

    And lastly, David, it would be so great if everybody could agree on a common language/conventions of all those key reference points for calculations. PHIUS has started to convert European Passive House language back into US building conventions to communicate with other programs, make the energy metric comparisons apples to apples and not oranges and to get government recognition. And it looks like that that makes a heck a lot of sense. After all, this is the context we exist in and need to communicate with (PHIUS+ and QAQC through RESNET harmonization is starting to look very good).

    I am so with you on the certified product thing. Makes no sense. Physics is physics, generate the protocols, the data, test it, publish it, that’s all we need to do. Window protocol coming up soon in next e-newsletter). And on that note, for my taste, EnerPHit looks like a step back to me as it is promoting prescriptive measures and certified components…

    Thank you, I keep track of all the ideas, first timeline for first draft proposal to tech committee is mid February, this will all inform it.


  18. Thanks for the post, Kat. I find the notion of changing the standard to be troublesome. I’m designing PH or near-PH buildings in Edmonton, which is at 53.5 degrees latitude, 10 000F heating degree days. I know of only Thorsten who’s trying to build these in a colder climate. Would a relaxed standard make it easier to build a Passive House? Sure. But doing this removes the challenge for us to build drastically better buildings.

    In conversations with PH colleagues from California, our standard building practices are roughly the same (2×6 fibreglass insulated wall). In a city of 1 million this far north, we should be ashamed. The great thing about the PH standard is that it challenges us to drastically sharpen our building skills (without turning to renewables). Is it hard to build a PH here? Yes. But you can do it for less money than current Net Zero Energy buildings cost, and there have been 12 of those built in the last few years. We have plans for a 200 unit, multi-tower mixed use development that will be built to the PH standard as is (Station Pointe Greens). The rigor of the standard is what attracts people to it.

    Being in Canada, we’re also dealing with both PHIUS & CanPHI, and CanPHI is a staunch supporter of the international standard. If PHIUS allows for a watered-down standard, then we’ll have to deal with market confusion; I completely agree with the others who posted here that a changed standard must have a different name.

    My personal opinion is that the standard should remain unchanged. If it’s too expensive for a project to meet the criteria, then budget will dictate that it falls short to some degree. Is this a bad thing for society? No, the building will still be massively better than the standard quo here. Is this a bad thing for PHIUS? If your goals are to build better buildings, then no. If your goals are to get more participants in a brand, then yes.

    Passive House presents a methodology to be used on ALL building projects; a tool in the tool kit. It’s also the highest bar around. Lowering the bar just reduces the incentive for change.

    Stuart Fix

    • Hi Stuart, always a pleasure talking with you! Indeed, only Thorsten and one fellow consultant in Whitehorse have attempted the almost impossible further north from where you are.

      Let me assure you, there is no intention to change the standard or to water it down. Refining it means to evaluate the physics principles that we are so proud of to be also accurate and holding true in a very cold climate. I agree with Martin wholeheartedly, the argument as it is currently proposed from the physics side of things does not hold water. In addition to that, in a milder climate, and you are mentioning your colleagues from California, the bar might move up and get more stringent.

      I do believe in the physics as basis. Before I give that up I’ll go and find another job :) . As I expressed earlier, not a big fan of prescriptive anything. The systems design truly is the beauty of it. That also means that those engaging in the design of Passive House structures need to be firmly in the saddle and understand the underlying physics and the complexity that comes with it and the moving targets. As I understand the physics,15 is a consequence of this underlying principle specific to a certain climate. It is a variable by definition, different in every climate. The fixed underlying relationship is the relationship between fresh air needs for IAQ and peak load capacity of that amount of air which if met results in pretty much the most efficient and cost effective state of equilibrium that one can attempt to build. That is the fixed physics relationship which is the same anywhere in the world. That is before you add climate to the equation. Meet that condition in a specific climate then from there you can now calculate which annual consumption that state results in. That’s how they arrived at the 15 in Darmstadt. That calculation needs to be performed in all different climates to arrive at the specific to the climate annual heat demand. In California, it might result in 8 kWh.

      This argument is not new. The Swedes have discussed it in Europe forever, even the PHI says the same thing on their iPHA website: it might be 10 in Rome and 20 in Stockholm.

      Let’s think it through and really know the physics behind this thing before we conclude. I think that is first order of business.

      As for the 15 being well-defined, based on everything cited here and the overall discussion, I have to disagree with Hayden. It has not long been well defined (see above). If it was all well defined and everybody agreed, I am with you here, what would be the point? But there is a very legitimate debate and discussion worth having.

      Looking forward to your thoughts!

    • Stuart, you have compelling ideas and state them clearly. Canada is not alone in having multiple Passive House certifying organizations: CanPHI is eligible to certify in the US. PHAccademy is active here, too. Certification is also available directly through the PHI. And more people from the US are headed to Darmstadt this summer to receive Independent Passive House Certifier training.

      Having PHIUS using one PH definition, while everyone else uses another, would create a mess that could easily be avoided. The solution is simple: give the PHIUS standard its own name, let the market choose, and may the best standard win. The PHIUS standard will have the obvious advantage of being easier to comply with – a no brainer for many projects.

      • Thanks for the response, Kat, these are exciting times! I agree with you that the physics behind designing a home within the heating capacity of a ventilation system is beautiful. My understanding is that in Germany, and in Alaska, and in Abu Dhabi, the amount of heat that can be delivered through 0.3ACH airflow is around 10W/m2. This is a climate-independent number; design your building within this load and you’ve minimized your mechanical system size, and that’s the best answer I’ve ever heard for “how far to take efficiency?”.

        Now here is where it gets confusing. My understanding is that in the early days the Scandinavians decided that 10W/m2 was too hard to meet, and in turn the Germans converted their 10W/m2 peak load design target into an equivalent annual heating demand target, our magical 15kWh/m2. Since cold climates tend to be sunnier climates, you can make a building that uses the same annual heating energy, though it will have a higher peak load than the ventilation can provide. This is where the physics justification of PH ended, and where the politics of brand expansion began. You can justify that the 15kWh/m2a produces equivalently energy efficient buildings anywhere, but the physics justification is muddled.

        If you wanted to drop this 15kWh/m2a from the standard, and return to the physics beauty of the 10W/m2a peak load target, I’d be all for it. BUT that’s even harder for northern climate practitioners than the current standard (When I optimize the snot out of a PH building, I can hit the 15kWh/m2a target with an R45 diaper, R60 roof, and top notch windows, but the peak load is always in the 15-20W/m2 range).

        Where is the physics justification for relaxing the heating demand target for northern climates, or tightening up the target for warmer climates? It seems like only a political move to help brand expansion.

        I don’t want to get dramatic here, I’d welcome another standard that sets a 30kWh/m2 heating target, that would represent an 80% reduction in heating energy as opposed to the 90% the standard provides now; these would still be tremendous buildings. But it would be a standard that sets an arbitrary target, with no physics background that I see.

        Am I missing something here?

        Stuart Fix

        • Stuart,

          You hit the nail on the head. Once you try to design to 10 W/sqm in Edmonton you will hit the physics Passive House wall. You can’t get there. There will need to be infinite amounts of insulation. The early Passive House people in the mid 70s knew that. This is why they might have overlooked the 10 W/sqm peak limit as significant (even though one of them wrote it into the Model Energy Code then, still today in the IECC). They tried to do this in Boise Idaho and realized, can’t do and threw it out as a universal design guideline. I think the general principle can help us to define the next peak limit threshold up though.

          So, I think we want to go back to that point, just as you are suggesting. Is there a physics relationship in regards to peak load that makes sense in Edmonton? I think there is.

          In many ways the 10 W/sqm are also not carved in stone. It is based on an educated assumption of how much fresh air a person needs. We have seen ventilation codes go up and down and up and down. So, lets say we are making a fair assumption and are in the ball park by averaging the ups and downs. Ok. We have fixed amount of air good for humans with the same heat capacity anywhere. Pretty straight forward. Same anywhere, climate independent. If you can limit heat loss to be at or below 10 you are probably finding yourself in a relatively mild climate (compared to Edmonton).

          The next thing to evaluate is, if there is a similar slightly higher peak we can make an argument for in a very cold climate? When I first started with this Passive House thing, I found myself sitting next to Gary Nelson having a beer talking about low flow delivery of space conditioning. He said, why don’t you just create a small recirc loop and your problem is solved. With only a few PHs under my belt in only one climate zone I did not understand Passive House enough at that time to allow myself to stray from the road. Now I believe he was right on with his comment (of course, himself a Passive pioneer veteran of many years). It does not take that many more cfms to get the space conditioning done in a cold climate in a superinsulated building. We can do this super energy and costefficiently with the low temp mini-splits. All we need to do is determine the new limit of the transportable peak load and make a good argument for it (maybe through economics, maybe through comfort). Stuart, you are doing this already. How much recirc is acceptable? How can we balance this with maybe slightly reduced insulation levels? Effectiveness of last inch of insulation indeed goes against zero if superinsulated in very cold climate. Can we make an argument to get rid of that last inch or two? This would result in slightly higher peaks, and you guessed it, a new magic annual number, climate specific. This number should not be far off from 15. I think the range of 10 in mild climates (similar argument there) and 20 in very cold ones should do it. I hope that that’s the finding we will make. Its about introducing an new balancing act. If we don’t ask the question we will see nothing. And then, ideally, we will have the physics again match the argument. Beautiful!

          • Thanks again for taking the time to explain this, Kat, I greatly appreciate it. I understand where you’re coming from and where you’d like to take the standard. I think this is a good initiative, if nothing else it will really break down things to a nuts & bolts level that can teach us all a few things. Better understanding lead to better buildings!


  19. As we say out West, “Calling your mule a horse doesn’t get you a horse.”

    Kat, I hope you are not closing the door with the no-need-for-renaming statement. Passive House has long been well defined both in North America and internationally. Having two definitions for Passive House, one for PHIUS, and one for everyone else, would be damaging to the Passive House community. Let the new PHIUS brand succeed on its own merits – not by association with a different standard.

  20. First, I sincerely appreciate this discussion. Thanks for opening it up Kat.

    I may be missing something here.
    Why the need to focus on the 4.75kBTU/(ft2yr) at all?

    Why not just use Specific Primary Energy Demand as currently limited, 38kBTU/(ft2yr)- cell # 97E of PE VALUE SHEET?
    As Jesse stated, the climate doesn’t care what process in occupying a building created the CO2, just what the overall emissions are. I’m showing my bias to CO2 emissions reductions here!
    We cannot heat our buildings here ( Northern Michigan) with the amount of energy that can be transported in the “supply air” for IAQ.
    That was never a requirement for a Passive House, just an optimal lure for a more moderate climate.

    I am not advocating for allowing those of us in cold climates to have a larger impact on the environment.

    In cold climates we can focus more on Solar DHW systems and highly efficient Space Heating Systems and energy carriers to stay within that limit. None of those are specifically required, but the DHW from solar is already allowed to be used to reduce the SPED, as is a SHX system. Both of these lend weight to Marc’s thoughts about PV being allowed to enter into the standard – within specific limits.

    That would push the energy carrier source towards the “local” and allow the savings in thermal insulation cost reductions to be used to help pay for those systems-
    Tunneling through the cost barrier for the north.

    In my climate I can remain “Net Neutral” in CO2 emissions in relation to the SPED, even if my SSHD goes above the PH limit of 4.75, by using the above approach.
    I still need PH quality windows-U value below 0.8 W/(m2K).
    I still need exterior building envelope elements to have a U-value below 0.15 W/(m2K)
    And I still need airtightness at ACH50 to be no higher than 0.6.
    I agree with what I think Marc and Jesse have stated- we have the wrong box colored in red on the verification sheet for cold climates. The SSHD/(ft2yr) is leading us down an “overall higher cost, for the same environmental outcome” path.

    I don’t believe this SPED focus would have an impact on comfort- relation of building interior surface temperatures to body temperature.
    Total energy consumption and CO2 emissions would remain within the 38kBTU/(ft2yr) limit.
    I fully support PHIUS in their approach to analyzing this issue and their right to “adapt” if it makes scientific sense.
    In terms of name changes- I don’t understand the fuss/anxiety. The overall outcome is what is important. The goal is the same. Overall energy consumption limits with regard to source implications, PE factor and thereby CO2 emissions. All while maintaining optimal IAQ, occupant comfort levels and building durability.


    • Steve, great comment! Detailed, thorough and clear. And…I am with you and Marc and Jesse on the PE value. Just said to a journalist yesterday: “The Source Energy is really the queen criteria in disguise”.

  21. I hope I am not too late to add to this discussion …

    I am currently finishing an engineering Master’s degree and my research has focused on developing a method for determining climate-dependent Passive House standards. I have thought a lot about the issues being discussed on this blog, I am very much in support of revising the standard to be climate-dependent, and I would like to add my two cents!

    I believe that climate-dependent Passive House standards are needed in the U.S. simply because there is such great variation in the climates found in the U.S. (more variation than across all of Europe). Applying just one standard to the entire U.S. will have two negative effects. First, it will discourage adoption of the standard in harsh climates (both cold and hot) where the standard is extremely challenging – only the most dedicated homeowner or builder will attempt to meet the standard there. Second, it will mean missing out on substantial potential energy savings in mild climates where the standard is relatively easy to achieve. Another way of saying all of this is that (i) an effective performance standard should represent a significant improvement over the typical approach while still being technically feasible and cost-competitive and (ii) a single standard cannot simultaneously achieve all three of these goals in every climate of the U.S.

    As Katrin has indicated, the PH standard does have a basis in physics. However, I would like to propose that the standard is, most fundamentally, the result of an investigation into the highest level of performance that is both technically feasible and cost-competitive in the German climate. With this in mind, I developed a method that would apply this same point of view to other climates in order to determine annual heating and cooling demand criteria. I believe that my method is consistent with what I see as the central tenet of the Passive House approach: design the house first and foremost to minimize the heating and cooling demand (the specification of efficient HVAC equipment, lighting, etc. comes later).

    My method uses two steps:
    i) Determine economic conditions under which houses built to the PH standard are cost-competitive in the German climate (i.e. where the additional construction costs will be repaid by savings on utility bills in a reasonable amount of time).
    ii) Apply the same economic conditions to another climate to determine the highest level of performance for that climate that is cost-competitive (and technically feasible)

    Application of the method to the U.S. led me to the conclusion that the existing standard should be relaxed in some parts of the country but should be tightened in others. In fact, the variation in heating and cooling demand criteria is likely to be quite large and regional standards should not be seen as just minor modifications to the current PH standard.

    Lastly I would like to second the suggestion made by John Essig above (on 2/2/12) that the two separate criteria for heating demand and cooling demand be combined into one criterion for the sum of the heating demand and cooling demand (possibly with the addition of humidification). Combining them gives the designer more flexibility to explore trade-offs between minimizing the heating demand and the cooling demand.

    Bruce Kruger
    Building Systems Program
    University of Colorado at Boulder

    P.S. If anyone is interested in my research, I do have a much longer write-up available!

    • Bruce,

      last we spoke was when I was in Portland, OR for the Passive House regional event up there. I am delayed in communications as the spring time is as always action packed with conferences all over the place and they are all getting so good! It is really difficult to give up on being present on any of them!
      Well, Bruce and I had a longer talk via phone during which he introduced me in more detail to his proposal. I do believe that his approach is one of the leads that we received from the community that the Tech Committee should in all earnest further investigate. Hopefully soon Bruce will have the opportunity to present to the committee.

      Bruce’s studie’s findings are eye opening. I truly believe that we as a community are embarking on the next level of passive standards evolution. Stay tuned, more soon.

    • Hi Bruce,

      I am an undergraduate student at Princeton University currently studying Passive House in the U.S. and I am obviously very interested in your work.

      I would also be very interested in your full write up. Please let me know if this is possible!

      Chris Hamm

  22. Hi Everyone:

    Thoroughly enjoyed the conversation here. I’d like to invite you all to continue this conversation face-to-face at the upcoming NESEA BuildingEnergy Conference, March 6-8 at the Boston World Trade Center. http://www.nesea.org/be12/

    Paul Eldrenkamp and I are organizing a Passive House dinner after the Tuesday night Opening Forum. We haven’t picked out a restaurant yet, but we’ll announce it at the Forum. To learn more about Passive House-related content at the show (including workshops by Kat and Marc Rosenbaum), see “Passive House Struts it’s Stuff at BuildingEnergy,” http://tinyurl.com/6w5g9ka

    For what it’s worth, I like the idea of PH4, PH7… too.

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  27. “””Having lived in a “Near Passive House” (not Certified) since November, 2008, I can say that it is the most comfortable house I have ever lived in while being the cheapest to operate”””

    I’m glad there was at least one commenter who is good with his/her “not Certified” near passive house. Same goes for all the hub bub meeting “LEED” standards, etc. My Gosh, just build homes that are smaller, use less energy, are closer to work, and more eco-friendly, then the market will decide their value.

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