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Striving for Passivhaus Affordability

Focusing on high performance and cost control, EcoCor Design/Build is completing a Passivhaus project in Maine

Tackling price and performance. EcoCor Design/Build is nearing completion on this 1,600-sq.-ft. home in Knox, Maine. The house has been built to meet Passivhaus requirements and a relatively tight budget.
Image Credit: Chris Corson
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Tackling price and performance. EcoCor Design/Build is nearing completion on this 1,600-sq.-ft. home in Knox, Maine. The house has been built to meet Passivhaus requirements and a relatively tight budget.
Image Credit: Chris Corson
The first time the house was tested for airtightness, EcoCor owner Chris Corson had only the rough shell in place, though it still showed only 0.545 air changes per hour at 50 Pascals pressure difference. The Intus triple-glazed windows used on the project were installed with brackets rather than window flanges. A blower-door test conducted after the shell was complete showed 0.286 ach @ 50 pa, builder Chris Corson says. The house is equipped with a Mitsubishi Mr. Slim heat pump and, for backup, electric baseboard heaters. The front of the house.

For builder Christian Corson, low numbers are good numbers. His current project, a 1,600-sq.-ft. two-bedroom Passivhaus in Knox, Maine, has been testing well and not costing much. A few months ago, for example, with just the rough shell in place – oriented-strand board sheathing on a timber frame, all taping done, and windows installed and sealed in place – the building showed 0.545 air changes per hour at 50 Pascals pressure difference.

There have been four blower-door tests since. The most recent, with construction essentially complete, Corson says, showed 0.286 ach50 – notably below the 0.6 ach50 Passivhaus requirement. In addition, the building’s annual heat demand is now at 3.1 Btu per sq. ft. – again well below the Passivhaus requirement, which is 4.75 Btu per sq. ft. (Modeling is based on 7,345 heating degree days.)

But the other encouraging low number, Corson adds, is $130 – the cost per square foot, including all site work on the 10-acre lot.

“This is the first step of an evolution for me to go beyond Passivhaus and do it affordably,” Corson, owner of EcoCor Design/Build, told GBA recently. “By exceeding the Passivhaus standard, it affords us some design flexibility down the road, so maybe we can deviate from the usual design, put more windows on the north side, and not be so committed to a single look.”

Push to NZE

The slab for this project sits on a platform of expanded polystyrene that is 12 in. thick and insulates to R-54. Corson avoided using spray polyurethane foam.

The exterior walls are insulated to R-58 with dense-packed cellulose; the ceiling is insulated to R-80 with loose-fill cellulose. Air conditioning and heat will be supplied by a Mitsubishi minisplit air-source heat pump, although the house also is equipped with electric baseboard heaters as backup.

The home’s triple-glazed vinyl-frame windows, made by a Lithuanian company, Intus Windows, are rated at just under R-9. Corson became a product representative for Intus because, he says, the company offers an exceptional combination of quality and price.

The project also includes a 1.4-kW photovoltaic system: six panels mounted on power rails that will affixed by brackets over the lower windows on the south side of the house. The PV system will bring the house to net-positive-energy operation – or very close to it.


  1. davidmeiland | | #1

    Is that complete, finished cost, or shell only?

  2. user-1026988 | | #2

    David, Good question.That is complete finished cost. It excludes the cost of the land and the PV. It includes site work, septic, road to the house, and total build out costs. The finishes are modern, fresh, modest and to a great degree...local. This home has truly minimized not only energy costs but embodied energy or source energy as well. The Silestone counter-top was an additional homeowner splurge.

    The PV system (additional 6000$ or so) which consists of 6 - 235w panels, is being financed by the homeowner with a little help from us. To not get this house to net -zero would in my opinion be a shame. After tax credits and rebates the house will be net zero or net positive for about 3 grand out of pocket. thinks so.

  3. user-1026988 | | #3

    Solar Panels
    Just to clarify. The PV system is not going on the roof. It will be fastened to power rails, that will in turn be fastened to the brackets that are cantilevered over the lower southern glazing. It will provide not only electricity, but summer shading as well. By having the panels low on the home we can also drastically mitigate winter losses.

  4. GBA Editor
    Richard Defendorf | | #4

    Thank you for the clarification, Chris
    The text on the PV system has been altered accordingly.

  5. hRsEXF3AMb | | #5

    It is so important for this
    It is so important for this type of construction to be available to the general public and I applaud you for making this possible. I was wondering how were you able to do this at such an affordable price when other builders charge a much higher rate for this type of construction?

  6. user-1026988 | | #6

    Thanks for the praise, Alexia. As far as I know there are VERY few builders building the way we do. Although careful planning, thoughtful design and diligent costing were crucial to our process ,we have evolved sort of experientially, through a process of designing and building super-insulated homes and arrived at a wall assembly that is efficient, durable, thermal bridge free,and easy to build. By building more efficiently we have kept costs down. We also paid great diligence to staying on budget at different points. Although this home is "semi-custom" and for a good part (from a design standpoint) client driven, we were given the latitude to make design decisions that we felt could enhance the project. Starting with how best to achieve PH. All of our energy modeling, design , and construction is done in house, so we have the capacity to communicate and collaborate, quickly and effectively in order to make prudent decisions, on the fly that enhance the process. We also believe that many designers and builders have "cashed in" on "green building" (a term I am always reluctant to use). I dont believe there should be an upcharge to live in a healthy, comfortable environment. I dont think that beauty needs to be a victim of affordability. At some point the "culture" of construction must change. That process I believe has begun, I hope to hasten it. We ALL deserve to live in a healthy environment, just like we deserve access to health care and education. Its ironic that the PH movement was nurtured to maturity in Europe and THEN came back to the US. I wish the same could be said of other social policies as well.

  7. hRsEXF3AMb | | #7

    Thank you for your detailed
    Thank you for your detailed response! I'm glad to finally see a builder not upcharging for "green building".

  8. user-869687 | | #8

    Christian, kudos for what you're doing...
    This country needs more people who think the way you do. I agree it should be possible for the same builder to keep a lid on cost for the homeowner, while taking performance seriously and being willing to experiment and innovate. I see builders falling generally into three camps: first the production builder who's not interested in going beyond code minimum; then the custom builder who works with architects and will build anything, but at very high cost; and third, the designer/developer or designer/builder who gets around the shortcomings of the first two (quality/cost). Evidently in Europe there are more builders who take pride in meeting PH performance standards, and don't view this as something reserved for very high-end projects. In fact I could see a trend toward not-so-high-end PH production based on life cycle cost (or even ownership cost per month).

  9. EthosNY | | #9

    Wall Assembly
    I am a builder that shares the philosophy that "green" doesn't have to (and shouldn't) come at a premium. I am curious about the details of the wall assembly that you have evolved.

  10. 2EekSFMmSa | | #10

    Nice work
    Great job here Christian. As others have noted it is SO nice to see that someone can build something so efficient and well thought out without needing a trust fund to do it with. I'm with John... Any chance we could see some details on how the house was constructed? This sounds like a very intriguing model.

  11. RdJ2MCNvnS | | #11

    A key element
    Congratulations Chris! It must be pointed out that the most important key element of passive house construction is commitment and perseverance by the builder. This tends to get overlooked because of our fascination with modeling and technical detail. We may compromise on those details, but if the commitment and perseverance are missing (or, worse, replaced by garden variety greed) all bets are off.

  12. CNTN46ixZU | | #12

    Even cheaper?
    Chris, It's hard to think that you could have done this project for even less $$, but given that you have WAY surpassed the energy metric of the PH standard, it seems to me that you could have spent less on insulation. Which would have made the project even cheaper and still hit PH standard!

    How much do you think you could have saved if you came closer to the 4.75 kBTU/yr/ft2? BTW I would never think to skimp on the ACH50 and nice job an the .286 ACH50!

    Also, is the 1,600 sq. ft. number TFA or gross sqaure footage?


  13. user-1026988 | | #13

    John and Chris
    First, I guess I should clarify. This assembly is part of my own personal evolution away from the double stud wall. I spent some time over the last couple if years trying to figure out a way to create a thermal bridge free double stud wall that was, vapor open (vapor permeable), used no SPF's,and could be easily airsealed in such a way that would mitigate the propensity for failure, and increase durability of the air barrier. I have never been a huge proponent of ADA's although in certain situations(mainley retrofits and very low budget projects) that approach can be very effective. But not durable.( although ADA's do have some appealing extraneous merits like being less susceptible to rodents.) My first order of business was to bring the load bearing part of the assembly to the inside stack the ceiling on that and point load to the trusses. Allowing the insulation plain to break the obvious connections. The big dilemma for me was how to thermally break the slab to mudsill connections while maintaining the integrity of the finished veneer surface on the outside of the wall. There were a bunch of other concerns and considerations as well but for the sake of brevity......
    Push to Dec. 2010.....I took the PH consultants training in NYC. I already had played around with the PHPP, was already pretty plugged in to PH, having traveled extensively and worked in Europe. I was also already in design phase of the house you see above. Katrin Klinginburg was talking about wall assemblies yada,yada, and put up this slide of an assembly that she had just used in a project of her own. As soon as I saw the slide it was like this great epiphany. It solved literally ALL of the issues I had been struggling with. She was gracious enough to share the details with me. I made some very minor tweaks, changed up some materials, redrew the assemblies in CAD for our PH and then went into production this spring. So....I mention this to be clear that this is no invention of my own, but rather a gift of the experience of Katrin (who herself had just made the leap to this assembly), and a few others (Bjorn?) in Europe, that are farther ahead of me in their experience of PH.

    The assembly is basically a 2x4 load bearing inner wall, piont loaded to the trusses 24oc OVE framing. With the OSB air barrier on the outside of the wall. Thus allowing the inner third of the wall to dry to the inside, and securing the integrity of the air barrior in the middle of the wall where it can not be damaged. The 2x4 wall is then strapped with 117/8 TJI's creating a box beam wall assembly that is "non load bearing" and cantilever over and onto the perimeter insulation. Then over that is a high perm fiber sheathing ~ 38 perms.
    IN to OUT

    5/8 rock
    2x4 wall 24oc OVE insulated with Roxul batts
    1/2 OSB air barrier
    11 7/8 TJI's insulated with 3.5lb cellulose
    1/2 high perm sheathing
    3/4 in strapping creating drainage/convection plain (rainscreen)
    Pine shiplap, and cedar shakes.

    The,the,the thats all folks!

  14. user-1026988 | | #14

    TFA is 1140 ft2. 1600 is Out to Out. Volume is 11100 (conservatively measured to DIN 13829). 53ish or below CFM/ -50Pa.
    Yes, it could be even cheaper if we used less insulation. However, by besting the standard, we have opened up a whole range of design possibilities, where we could fudge glazing ratio's, put more windows on the north. allow for less compact footprints, cantilever second story bumpouts etc.
    Also just because the construction costs would be cheaper doesn't necessarily mean the product would cost less in the marketplace.
    Although our company did turn a profit on this home..... I far. It is a very modest one. It in no way pays for my personal time invested in this particular project. I would build this exact home or reasonable variation of it for the same price, all day long,but for even would I pay for NESEA? If I was building homes like i used too,.........beautiful pigs of homes..............well then I wouldn't be here now.

    I know this may seem contradictory, but there does need to be a balance between changing the culture of construction, and running a business, I hope to truly find that balance some day. If a 120.ft2 PH fits into that then GREAT!

  15. NrhUsEzvwc | | #15

    Great Job.
    Let me say again what a great job you did on this house.

    But most of all I want to thank you for a number: $130/ square foot. Often when advising people on building a green house, various numbers are pulled out like "10-15% more than conventional". Now, I plan to use your $130 / square foot. Given that a number of builders won't even talk to you for less than $250 / square foot, this just pulls the rug out from under the argument that building in this way is more expensive.

  16. user-723121 | | #16

    Builders subsidizing energy efficient homes
    Don't do it, you must make a fair profit on every job. A house built to Passive House standards should command a better price than a BAU house. Total all of your costs and add a profit margin, this is the only way to stay in business.

    Great job Christian and thank you for sharing the cost per sf. Make sure you are compensated adequately for your time and expertise, there are but a handful of builders who can turn out such a product.

  17. user-1078381 | | #17

    Kudos Chris
    Glad to see it finished and certified. You are one of my heroes. I just got my first consult job for a PH and love your use of insulation with low embedded energy. You are on the forefront! Reasonable cost on PH is the future! Can I invite you to come to Vt and give a talk on your building details to local builders?

  18. B_Carr | | #18

    Great job Christian
    Thank you and congrats on a job well done Christian. Completing such a project on, or even near, $130/sf is encouraging. I especially love the use of a mini-split for most (if not all) air conditioning and heating needs. Can you explain your rationale behind using TJI’s versus the conventional Larsen truss system? Was it chosen from a cost standpoint, ease or necessity of installation, or for other reasons? Also, any marketability concerns from your standpoint regarding the reduced interior square-footage from a 18-inch wall assembly?

  19. user-1026988 | | #19

    Thanks Brad
    The ASHP exceeds our peak heat load considerably. Our heat load at a design temp of -5F is just under 5600 btu/hr or about 1800w. This is in Maine with 7300+ HDD.
    Although I think that Larson trusses are great for some applications in DER's , I would not personally use them in new construction. I find that working with TJI's is faster and easier , and TJI's are engineered for structural wall assemblies( in Europe). They are MUCH stronger than Larson trusses and are not prone to sag. In this assembly tji's are cantilevered over the perimeter insulation(which is in itself structural).
    There is no correlation between the size of the wall assembly and the size of the interior living space, or Treated floor area in the PHPP. The house is a custom design for clients, their requirements for interior living space and their budget defined the size of the living area, the walls came after that. If they were 30 in thick it shouldn't change a thing. Except maybe the appraisal value, since those valuations are based on the ext dimensions.
    cheers. Thanks for the comments.

  20. N3y2cNDw2m | | #20

    I love what you're doing here in Maine.

    We should chat. I'm looking to break ground this Fall about a half hour away from you. My land is in Union.


  21. user-2069108 | | #21

    Asking for specifics
    First of all, my understanding of Advanced Framing is that the load wall should be 2x6's. How did you do this with 2x4's?
    I admire the simplicity of your wall assembly. Further, I am pleased that a R58 wall is good enough for PH. I had been considering a triple wall; Drywall - 2x4 non load chase wall 24"OC - OSB Air barrier, taped of Sto'ed - 2x6 Structural wall 24"OC - Fiberboard - Larsen Truss - Fiberboard - Siding assembly of some sort. All Cavities filled with dense pack or wet spray Cellulose.
    Would it be possible to get a breakdown of the costs associated with the construction? Shell, windows, mechanical systems - the things that make this a Passive House.

  22. user-1026988 | | #22

    OVE framing is about reduction of volume of lumber in the wall assembly. Thus decreasing the conductivity of the wall. Whether it is 2 x 4 or 2 x 6 is up to your designer and or engineer. OVE framing principle operate on the concept of point loads v. distributed loads.
    In our case we use 2 x 4 with double tops and double sole plates. All corners are screwed together. In fact we probably use more screws framing than anyone else I know. All plates and corners are screwed with GRK r 4's and or RSS lags. Engineers like screws and so do I.

    Many homes and barns have been built with balloon framed 2 x 4's throughout New England and lots of them are 100 years old. I grew up in one built in 1780's.

    As for R 58 walls being " good enough for PH" I will say a couple of things.

    First, I do not believe in prescriptive solutions. Each home ,each geometry, each situation is mostly unique ( in my world of custom residential) . Different S to V ratios, truss packages, building height limits , coastal zones, etc all can affect design parameters.
    That being said one of the guiding principles in the design of this home was replicability, and a potential to use this wall assembly in ANY climate zone. R-58 is a good baseline from which to start.
    IMHO Larson trusses and fiberboard is a bad combination. Refer to a structural engineer on that one.
    At this time it is not possible to get a specific breakdown of costs associated with this particular project, sorry.
    If you read the article I wrote for JLC all of the info is available and most components could be easily costed by yourself.

    As a sub note I will also say that I have moved away from fiberboard all together. We are now using membranes as these products have become available in the United States.

    We are using these ( Solotex Mento Plus) for our walls and roofs.

    Still evolving

  23. user-2069108 | | #23

    Response to CC
    I am not an engineer, but I am an avid DIYer and I am learning a whole lot about high insulation walls, premium windows, moisture issues in walls and green building techniques.
    My comment about the 2x4 wall was based on Advanced Building litriture that I read. I am glad that you were able to use the thinner walls in your construction, with the screws and doubling of plates.
    My comment regarding the R58 walls was meant to indicate that you did well to achieve PH with that level of insulation. I was, mistakenly, thinking that a much higher insulation value was needed. (I realise that the volume to surface area ratio is important in this determination, also.)
    The walls that I described are based on a dry to the outside system somewhat like that used on the houses in Champaign-Urbana, with fiberboard on the outside to allow drying. It is also a method that a DIYer can handle.
    How were you able to offset your structural wall from your insulation wall? That is, how did you attach your I beams to the wall? Were you able to screw them through the OSB? Is this why you do not like the structural fiberboard in my plan?
    (I am sorry if you have this all in your JLC article but no matter what I try, I cannot subscribe to their service)

  24. chadludeman | | #24

    Definition of NZE
    I know this is an old post, but if anyone is still responding I'm curious about the definition of Net Zero Energy used here. The claim of getting to NZE with only 1.4 kW array sounds more like Net Zero Dollars than energy. Having built a few homes near these specs, the HERS modeling does not get close to true NZE without something closer to 5 kW. There may be some confusion from PHIUS training as we've seen multiple PH projects claim to be getting to NZE on tiny arrays. This is a great goal, we just need to be cautious of how we are all reporting this so everyone can learn equally from the results...

    Great project. Keep it up.

  25. GBA Editor
    Martin Holladay | | #25

    Response to Chad Ludeman
    I also share your skepticism toward the claim that a 1.4-kW PV system can bring this house to net-zero energy. Of course, the proof is in the pudding... that is, 12 months of utility bills.

    I'll send an e-mail to Chris Corson to ask him if he has any utility bill information.

  26. aaronkelly95 | | #26

    Two questions:
    Is it possible to make the blueprints of this house available so that others wishing to replicate or emulate the design and building techniques can have some detailed documentation to work off of?
    Also, is there a good website where you can find blueprints for net-zero energy and passive homes?

  27. deb1221 | | #27

    I realize this is a 10 year old post but am very interested in more details such as the floor plan. I have searched the internet on this project but can't find anything else.

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