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Green Building News

The First Passivhaus Retrofit Certification in the U.S.

A deep energy renovation in California goes the distance; now it will be monitored for ongoing performance

Making the grade. Located in Sonoma, California, the retrofitted house in this rendering was, based on its performance, certified by Passive House Institute U.S. in early July. The builder, Solar Knights Construction, announced the achievement on July 20.
Image Credit: credit: Tomasz Biernacki, Pechara Studio Inc. (image 1), Solar Knights Construction (all other images)
View Gallery 8 images
Making the grade. Located in Sonoma, California, the retrofitted house in this rendering was, based on its performance, certified by Passive House Institute U.S. in early July. The builder, Solar Knights Construction, announced the achievement on July 20.
Image Credit: credit: Tomasz Biernacki, Pechara Studio Inc. (image 1), Solar Knights Construction (all other images)
A view of the O’Neill property from the street, before work began. Concrete from the demolished patio was used for landscaping walls. The remodel included a 400-sq.-ft. addition. The house acquired a U shape as a result of the renovation, requiring a relatively intricate system of HVAC duct runs. The retrofit applied the Pressure-Equalized Rain-Screen Insulated Structure Technique, with insulation and barriers such as Aerogel Spaceloft, InsulFoam IX expanded polystyrene, Insulfoam R-Tech IV rigid foam, Optima blow-in insulation, Grace Ice & Water Shield. The first layer of 2.5-in. expanded polystyrene. The second layer of expanded polystyrene: 1.25-in. R-Tec, with a radiant barrier at the window buck. Optiwin 3 Wood window frame prepped for installation.

UPDATED on March 30, 2011 with a new link at the bottom of the page to a video of the project.

The messy, retrofitting part is over. Now it’s time to track the performance of Cathy O’Neill’s 1960s-era home in Sonoma, California, which was expanded and renovated to the Passivhaus standard.

Last time we checked in on the project, in late March, builder Rick Milburn, of Solar Knights Construction in nearby Napa, was leading his team through the particulars of insulating and sealing about 40% of the existing envelope and a 400-sq.-ft. extension using the Pressure-Equalized Rain-Screen Insulated Structure Technique, with insulation and barriers that include Aerogel Spaceloft, InsulFoam IX expanded polystyrene, Insulfoam R-Tech IV rigid foam, Optima blow-in insulation, Grace Ice & Water Shield; Stego Wrap, and Protecto Wrap building tape.

The aim was to bring the floors to between R-12 and R-20, the roof to R-74, and the exterior walls to R-31, and add Optiwin 3 Wood triple-glazed windows and doors. The HVAC package includes an UltimateAir RecoupAerator energy recovery ventilator that, Milburn recently told Contractor magazine, likely will be used about 10 or 12 days a year, and only at about 30% capacity. The house originally featured 2,400 sq. ft. of interior space and radiant heated floors that were supplemented by electric baseboard heaters.

Savoring the results

All the planning and effort finally found their intended target. On July 20, Solar Knights announced that the house had earned certification from Passive House Institute US, making it the first residential retrofit in the United States to do so. Having made the unusual journey from retrofit candidate to Passivhaus performer, the house also will be monitored by the Department of Energy’s Lawrence Berkeley National Laboratory, and has been selected as a prototype by the DOE’s Building America Program.

For Milburn, the project was both demanding and enormously rewarding. “I will say that this is the hardest house I have ever built, but everything from here on out will be easy,” he told Contractor. “In the climate that I work in, there is no reason that all new construction shouldn’t be built to the Passivhaus standard. It’s just not that hard.”

To see a video tour of the project, click here.


  1. Expert Member
    Carl Seville | | #1

    Retrofit? Really?
    Not to diminish the performance level of this project, but when you strip a house down to the framing on both the interior and the exterior, it may be stretching the point to call it a retrofit. Its fine that they saved the foundation and a little framing, but this is RINO - Retrofit in Name Only. As a research project or one-off high end project, I am fine with it. But if we see projects like this as mainstream, I think we are deluding ourselves as building professionals. We need to look at making modest improvements to millions of homes instead of making just a few super high performing if we ever hope to make a difference in our existing housing stock.

  2. Graham Irwin | | #2

    Ventilation Use
    The energy recovery ventilation (ERV) system will be used a good deal more than 10-12 days per year, it will be used during the entire season when the outdoor temperature is below comfort level and the doors and windows are closed, and for night flushing in summer. During its operation, it will deliver a continuous stream of fresh air into the building at levels that exceed the ASHRAE requirements, at the same time retaining internal heat gains from cooking, bathing, lighting, etc. It is the air to air heat pump that will be used only occasionally, since it serves as back up for the "heat recycling" that the ERV provides, passive solar gains and night cooling.

  3. Graham Irwin | | #3

    Retrofit REALLY!!!
    The project was certainly an extremely extensive retrofit, but the building would have undergone the same level of demolition/reconstruction regardless of the energy goals due to its existing condition. It is more significant, in this case, to look at the INCREMENTAL difference in construction to reach the level of performance attained.
    Beyond that, this building is a prototype. I, the builder, and the rest of the team recognize that the methods employed need to be streamlined, economized and mass-produced to meet the needs of our country's existing housing stock, but we are confident this can happen, as it has in Europe. Making modest improvements to millions of homes will only slightly reduce our enormous shortfall in terms of energy use and climate change reduction - we are that far off the mark at present. Onward and upward, I say!!!

  4. GBA Editor
    Martin Holladay | | #4

    Question for Graham Irwin
    Thanks for posting here. Would you be willing to share the total project budget?

  5. Graham Irwin | | #5

    Check with the Contractor
    I don't know the budget, but I do know that it was completed within a 15% additional allowance for Passive House above code minimum.

  6. GBA Editor
    Martin Holladay | | #6

    What does that mean?
    What is this "additional allowance"? Who allowed it? What was 100% of the allowance supposed to be? What does 15% of the allowance mean? Why was it "additional"?

  7. Expert Member
    Carl Seville | | #7

    Modest vs Massive Changes
    Graham - To even imagine that a large number of retrofit projects can achieve this level of improvement, or anything even approaching it is a pipe dream. In many cases like this you reach a point where you may as well just build a new house rather than renovate an existing one. I agree that if you are doing a gut remodel anyway, sure go for the gold, but very few existing homes will ever go through this level of renovation and we need to make sure that every renovation goes as far as possible within the physical and financial constraints of each project. We can very easily improve the performance of any existing home by 10,20,30% or more with simple, manageable changes in our current processes. On top of that, owner behavior, if we could ever change it, could save as much or more energy than physical changes in the structure. I am afraid that when the uber efficient retrofits are promoted to the detriment of solid home performance and straightforward energy efficient and green remodels, then many professionals just throw up their hands an don't bother to do anything. We need to encourage everyone to improve the efficiency of each project incrementally so they learn. Almost anyone who tries to go this far at the start will drown trying to drink from the firehose. They need to sip slowly, and add to their repertoire little by little until the reach as high a level of performance as possible.

  8. Graham Irwin | | #8


    Apparently the contractor estimated that the project would cost 15% more to build as a Passive House over code minimum and it was completed on that schedule. It cost more because code minimum is 2x4 walls with R-13 fiberglass batts, R-19 ceiling and some slab edge insulation and cheap dual pane windows, a bathroom fan for a ventilation system and no air tightness requirement.

    This house is clearly a starting point, as "FIRST certified Passive House retrofit in the US" implies. Lessons were learned and attention is being paid to making this simpler and more affordable, as it must become for it to make a widespread impact. I don't know what metrics you are using to judge the imperative for improvement, Carl, but 10-30% improvement in our building stock isn't going to solve any real problems and, in fact, retrofitting buildings to a poor level of performance very often acts as a barrier to further improvement, because the investment has been made and, in many cases, the client burned by very little improvement for their time, effort and money. I cannot forecast what the future holds, but I do know that 70-90% energy reductions in building energy use are available and feasible today and in Europe, where Passive House has a 20 year old industry behind it, retrofits and new construction are commonplace. I would argue that incrementalism is promoted at the expense of retrofits, remodels and new construction that really makes a difference, and that property owners who really want to make a difference are done a disservice. This is an established method, there are plenty of built examples out there, and education and support for those who wish to become involved. As a country, we've been operating on the mantra of "this building is good enough" and "efficiency doesn't really matter" for far too long - we need to get ambitious and strive for excellence and world leadership, IM(H)O. The "gentlemanly-C" in building performance is a failed approach. I have faith in America to get up to speed quickly, to innovate and excel. This is the challenge of our age.

  9. Expert Member
    Carl Seville | | #9

    Graham, I don't disagree with you that extremely high level retrofits are possible, I but I believe that they are impractical in the sense that so few building professionals are capable of doing them. If we don't do anything on existing homes until we can start making them 50-90% more efficient, then you and I are going to be long dead and buried before much of anything happens. People need to step into high performance buildings at a level that they can absorb. If you took the average contractor and told them to do make their next renovation 50% more efficient, chances are they would fail miserably. There is simply too much to learn, and for them to drink from that firehose would only drown them and most likely delivery a poorly performing house to the homeowner in the process. Personally, I would rather see some solid, modest changes in every single project than have to wait until my resurrection to see lots of super efficient homes.

  10. Beth | | #10

    So We Settle?
    Carl, so we settle for just OK? It's not that difficult to build efficiently, given resources and education. "Average" contractors have access to a myriad of resources, many of them free, in order to further their understanding and knowledge of building techniques that deliver that energy performance you're talking about. As Graham pointed out earlier, we can't achieve our energy reduction goals by just reducing them by 10-20-30 percent. California has a bill (AB-32) that suggests that we retrofit in a crazy quilt set of benchmarks that ultimately require that by 2020, we get to Point B. By the time we reach point B we need to retrofit all those buildings we modestly tried to improve during this time to meet the 2020 standards. Because they will no longer comply. What a boon for remodelers. And what a waste of time and, more important, energy. We can do this now, without all of the incrementalism and wasted energy.

  11. GBA Editor
    Martin Holladay | | #11

    Beth, how much did it cost?
    I'm guessing this retrofit cost between $600,000 and $1,000,000. If Graham is willing to step forward with the actual budget, I'd love to be proved wrong.

  12. Graham Irwin | | #12

    I don't know.

    The budget is a private matter between the client and the builder, I was not made privy to it, though I did extensive work in cost-optimizing the shell with the builder and architect using an Integrated Design Process. Assume it was an expensive job (it's a beautiful, high end home.) The fixtures and finishes aside, it has modeled at an 80% reduction in source energy over a typical CA house that size. As such, this building already exceeds the state mandates for 2020 before photovoltaics are even factored in. The client is thrilled, the contractor is convinced and proud, and real progress has been made here in energy reduction, at an incremental cost of ~15%. Does anyone suggest that every home in California will be remodeled at this level? No. But PH construction gets cheaper and easier with practice and we have got to make major changes in how buildings are constructed and remodeled in this country. I have no interest in focusing on what CAN'T be done, or how this is supposedly beyond the capabilities of US builders (I know a fair number who have risen to the challenge in this immediate area.) I want to focus on what HAS been done, what IS possible, what IS working and what we CAN do to further this effort and increase accessibility. Everyone, IM(H)O, deserves to live in a comfortable, healthy home with low utility bills and environmental impact, and I believe that you should aim high - rarely does one exceed the expectations set out for oneself and low expectations produce mediocre results rather reliably. If you or other readers are interested in what else is happening in California right now, check this out:

    Also, the national Passive House Conference is coming up November 4-7 in Portland, OR:


  13. Expert Member
    Carl Seville | | #13

    Beth - We Can't (Practically) Do it Now
    I agree that the technology exists to dramatically reduce energy consumption in buildings, but we have neither enough suitably skilled professionals nor the financial ability to accomplish this in the short term. (The only way this will happen quickly is if energy costs skyrocket or supplies disappear overnight, neither of which is likely to happen as our country doesn't have the stomach to pay what energy really costs). Anyone who wants to take on a Passivehouse or zero energy project, all power to them, but they are at the beginning of the adoption curve and are breaking the trail for everyone who will follow on their own time frame. Mainstream construction can not get there in the short term.

    Beyond the actual building construction or renovation, we need to realize that owner behavior has as much or more effect on the actual energy use than the technologies use in construction. There are far too many people who leave lights on, keep HVAC running with windows and doors open, turn their thermostats up very high in winter and low in the summer, not to mention that they have dozens of high power vampire loads like TVs, cable boxes, etc. You can build all the high performance homes you want, but until you get the occupants to actually conserve energy, we will not accomplish any where near as much as we can or need to in the long run.

  14. Graham Irwin | | #14

    Yes We Can!!!
    Yes, this is trail blazing at this point, in the state of California and in this country, but Passive House has a 20 year track record in Europe, and their PH industry has matured to the point that new construction single family homes cost no more than 10% above standard and multi family cost the same, and over the life cycle of the building, nothing is cheaper. As for retrofits, hundreds of buildings are being modernized, in both performance and aesthetics. We do not need to reinvent this wheel, we can jump on board.

    "Owner behavior has as much or more effect on the actual energy use than the technologies use in construction." Absolutely not, in the case of Passive House. First, people respond to comfort, or lack thereof. Passive House not only performs better, but offers vastly superior comfort due to a lack of hot and cold spots in the interior of the shell. Furthermore, the ventilation system provides reliable and superior fresh air to what people get (or don't get) through their open windows and leaky buildings.

    Secondly, the mechanical systems are radically downsized. As an example, a 100,000 Btu/hr furnace (typical for a building like the O'Neill house pre-retrofit) is equivalent to a 30 kW load when it's running. That's a lot of cable boxes!!! The peak heating load for the O'Neill residence after retrofit is about 2 kW, roughly the capacity of a large hair dryer. In California, space heating and water heating are the two largest loads in a typical home, at roughly 30% each, and both of these have been radically reduced in this project, by 88% and 76%, respectively. The Passive House standard requires extensive attention to efficiency in all aspects of the building to meet the source energy limit, and the O'Neill residence has a predicted 80% source energy reduction over a typical California house.

    No, Passive House does not control the devices people plug into their outlets, nor how they use them (nor should it, IM(H)O) but it provides a "Prius" type building, which both attracts and encourages the inhabitants to be mindful of energy use. This contrasts with a typical building, which both discourages (through discomfort) and renders futile (through poor overall performance) attempts of most people to conserve energy.

    Performance monitoring in Europe has confirmed this - while there is still a very similar distribution curve of energy use across identical non-PH and PH buildings, it is only similar in terms of % of energy use difference, not absolute energy use - the PH buildings use far far less energy, even with the most inefficient occupants. These occupants (as I suggested above) lack the same "tools for inefficiency" that non-PH buildings provide, namely large fossil-fuel fired space conditioning equipment.

    The main stream construction industry can ABSOLUTELY come up to speed in the short term, and it will become easier and easier - it's a matter of setting high goals and working to reach them, not looking for excuses to fail or to do the same old stuff.

  15. Expert Member
    Carl Seville | | #15

    You overestimate Americans
    Apparently you have not observed that our country is largely populated by lazy, greedy, stupid (or stupidly acting) individuals who have no interest in doing anything positive for the environment or our national security. The followers of this site, and a small minority of others, being the exceptions. Until energy costs rise to the equivalent level of other countries, there will never be enough demand to make Passivehouse common. I look forward to the day when energy is so expensive that everyone wants to conserve. Until then, we can only expect incremental changes.

  16. Graham Irwin | | #16

    Which trend do you support?

    While you appear to lament a halfhearted attempt at solving these problems, you have spent much of your time in this exchange arguing for it. Ironically, if one comes here for "green building advice" one is told that it's basically a futile exercise! Might be worth a look...


  17. Expert Member
    Carl Seville | | #17

    Would love to see it, just don't believe we have the will
    I would love to see all existing buildings (except for those that are beyond hope and should be demolished) retrofitted to exceptional performance. I just don't believe that we have the will or enough trained professional to do it. And I do believe that promoting projects like this as something that can in the short term become mainstream practice is being somewhere between unrealistic and delusional. While I realize that technically we are capable of making this big change, practically it will take a very long time. Very few people are capable of rapid, dramatic change in their behavior except, possible, in the case of a major crisis like fuel scarcity, war, etc. As I mentioned before, if energy costs increased dramatically, we would probably make these changes very quickly. But the forces that be will never let that happen, so we must be willing to make incremental changes as we work our way towards a country full of high performance homes.

  18. GBA Editor
    Martin Holladay | | #18

    It cost $1.2 million
    In my September 16 post, I wrote, "I'm guessing this retrofit cost between $600,000 and $1,000,000. If Graham is willing to step forward with the actual budget, I'd love to be proved wrong."

    Once again, I'm proved wrong. The retrofit project cost $1.2 million, according to this article:

    That's $500 per square foot.

  19. Andrew Minsk | | #19

    the retrofit model
    Sonoma has to have one of the most benign and livable climates in the country. So the payoff will be, what, 150 years? To someone living in Wisconsin, every house in Sonoma is already a passive house. This retrofit model needs to be happening in Minneapolis, Buffalo, Burlington, VT.

  20. Graham Irwin | | #20

    Passive House is climate dependent

    The Passive House approach is performance-based, so the envelope measures required vary by climate. The Passive House in Sonoma achieves lower overall absolute reductions (though still an estimated 80% decrease in total energy use) but requires far less than it would in more extreme climates. The difference between code compliant construction and Passive House is not large in California (where we have relatively strict energy codes by US standards) but it's impact is enormous. California, if it were a country, is about #16 in the world for total carbon emissions. We've done a lot since Title 24 was instituted in the 1970s and have lofty goals for zero energy. A conventional home in California doesn't have the roof space for a PV system to produce that much energy. The Sonoma house is easily zero energy or energy plus.

  21. Graham Irwin | | #21


    As I mentioned previously, I did the energy modeling and Passive House consulting on this job, I was not privy to the construction budget, nor am I still. I don't know where the figure you quote came from, nor can I confirm or deny it.

    As you well know, however, much of the cost was not due to shell improvements. The building was a tough one: uninsulated slabs, convoluted and spread out single story envelope, low solar exposure. It basically got a few inches of EPS foam on the outside of a standard insulated envelope and better windows and doors. The slab, which was existing and previously uninsulated, was covered with between 1-1/2 and 4 inches of EPS, due to headroom requirements and varying heights. On the portion of the slab which could only accommodate 2 inches of height increase, we supplemented the 1-1/2 inches of EPS with 0.6 inches of Aerogel, which is quite expensive, but R-10 per inch. For this effort, the building has no dedicated central heating or cooling system, its peak heating load is 2000 W and its peak cooling load 1500 W.

    This was the first certified Passive House retrofit in the US and the first certified Passive House in California, so it was a prototype and a learning experience - all of us expect it will get easier and cheaper as we go, and we are very encouraged. The client is thrilled and proud to have done something groundbreaking and meaningful for climate change and energy independence. I don't think she deserves scorn. She could very easily have chosen to build a "green" home that did little to reduce its energy requirements, or perhaps exceeded the typical. This building "walks the talk" as it were.

  22. Dave | | #22

    Is this a more practical approach?
    RE: previous postings about the cost of this project ($500/sq ft) vs simple payback, check out what Dave Robinson (Green Earth Equities) has done in Sacramento, CA ( Basically a gut-rehab similar to this project, but less intensive (and he's making a profit). Passive certification is grand, but exterior wall top cavities are still generally too small for the proper amount of insulation (to meet either Energy Star or Passive standards), so retrofit projects will continue to be "as good as we can get it" given the technology of the day.

  23. Graham Irwin | | #23

    Yes, it is more practical in the long term
    The incremental cost between gutting an existing building and putting it back together at code minimum energy efficiency and to reach Passive House in mild climates is rather small. First cost does not even support code minimum efficiency, which is why there is code minimum in the first place. Over the long term, the O'Neill house is likely to remain ahead of the efficiency curve for many years to come. Buildings constructed to code minimum are energy liabilities to society in the present and in the near future. I am not against people making a living in the present, but we ought think about the future too.

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