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Musings of an Energy Nerd

The Klingenberg Wall

To build a high-R wall, Katrin Klingenberg recommends using I-joists for studs, fiberboard for exterior sheathing, and interior OSB as an air barrier and vapor retarder

The walls of this Passivhaus are framed with I-joists. The exterior sheathing is fiberboard, which is more vapor-permeable than OSB. Located on Fairview Avenue in Urbana, Illinois, the house was designed by Katrin Klingenberg. It was completed in 2006.
Image Credit: Katrin Klingenberg

When Katrin Klingenberg designed the first single-family Passivhaus in the U.S. in 2003, she used 12-inch-deep I-joists (TJIs) as wall studs. Located in Urbana, Illinois, the house was sheathed on the exterior side of the vertical I-joists with vapor-permeable fiberboard and on the interior with OSB, which acted as an interior air barrier, an interior vapor retarder, and structural bracing. The bays of the engineered studs were filled with blown-in fiberglass insulation.

In 2007, Klingenberg explained the principles behind her preferred wall design: “OSB has a vapor permeability of about 0.8 (considered to be semi-impermeable; that’s why we use it as vapor retarder on the inside of our frame work). … The rule of thumb for designing a diffusion-open wall assembly in heating climates is, that the outside sheathing should have a minimum of five times the permeability of the inside vapor retarder … So, with the use of the bituminous-coated structural fiberboard on the outside of our wall assemblies we are just in range.”

Klingenberg used the same wall system on several subsequent projects, including two single-family homes on Fairview Avenue in Urbana, Illinois.

In 2004, I interviewed Tom Huettner, one of the carpenters who (along with Ed Sindelar) built the first Klingenberg-designed Passivhaus in 2003. Huettner explained that the wall system was “based on a German design.” Klingenberg told me that she consulted a German document (“Balloon und Platform Framing Details”) published by Weyerhauser. Because aspects of this wall assembly have roots in Germany, many American builders assume that the system is common in Europe. In fact, few European builders use the system.

After completing her house, Klingenberg went on to found the Passive House Institute U.S. Klingenberg is a frequent public speaker on the topic of Passivhaus construction techniques, so her wall details have been copied by cold-climate builders all over the…

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  1. dickrussell | | #1

    On thermal bridging at rim
    The blog states: "Straube is a fan of walls that include a layer of insulation (either rigid foam or mineral wool) on the exterior side of the wall sheathing. One advantage of this approach is that it addresses thermal bridging and air leaks at rim joists."

    The double wall can easily cover thermal bridging at the rim joist simply by running the outer wall studs down to the sill, with the floor system (joists, rim, subfloor), with inner wall mounted on that, not extending past the minimum bearing area on the sill. This puts the rim on the inside of the wall cavity and is insulated as part of that cavity. Air sealing is handled by laying a bead of acoustic sealant on the sill before the rim is placed there and on top of the rim before the subfloor is placed. I've posted a diagram of this here before.

  2. user-757117 | | #2

    Further to Dick Russell's comment...
    I agree with Dick that a double wall can easily be designed to address thermal bridging at the rim board - while this may be a limitation to the "Klingenberg wall" it certainly doesn't have to be with other double wall approaches.

    The answer to some of the problems [with the Klingenberg approach] is to just build another wall on the inside, so you have somewhere to put the wiring on the interior of the air barrier. This is classic European thinking by non-builders. These are people who understand the building physics. But what about the labor? What about the cost?

    I don't agree that service cavities in general are some kind of cost albatross - it depends.

    With all due respect to the fellows at BSC, it sometimes seems they have somewhat of an obsession with the idea of a "one size fits all" solution to energy efficient and durable residential construction.
    I'm not-so-sure "one size fits all" is that important.

  3. user-626934 | | #3

    Larsen Truss

    There are some key differences between Larsen Truss walls and load-bearing TJI walls, but you lump them all into one category you're calling a "Klingenberg Wall", though Katrin invented neither. It's been at least four years since Katrin moved away from designing with load-bearing TJI's and switched to a slight variation of a Larsen Truss wall, that uses TJI's for the exterior insulation box to save on cost (vs. a site-built truss with 2x2 chords and 1x or plywood gussets).

    See, for example, Darcy Bean's presentation from the 2010 North American Passive House Conference -

    The key elements of Larsen Truss walls that are appealing improvements over using load-bearing TJI's include:

    1) "Business as usual" structural framing using 2x4's or 2x6's...easy for framers and easy for code officials to understand and stand behind.

    2) Larsen Truss walls use the standard structural sheathing (typically osb or plywood) as the air barrier, with all seams taped or sealed with a fluid-applied air barrier. Air leakage at the floor joists is eliminated.

    3) The insulation trusses are typically continuous from sill plate to topmost top plate, greatly reducing thermal bridging at the floor joist.

    4) To quote your quote from John Straube: "If you install insulation on the exterior side of the wall sheathing, you get to put the airtight layer in the middle of the wall. It works in all climates, and there is no need for a special service wall, and there is no need to change the usual framing package. All I have to change is my cladding attachment details and my window installation details.” Sounds like a Larsen Truss to me (though rigid exterior insulation would also fit the bill).

    5) The thermal transition from the framed wall to the slab or foundation wall is improved, since the Larsen Truss can "hang" over a thicker section of slab insulation...whereas the load-bearing TJI needs to bear on concrete.

  4. Expert Member

    It seems to me like the part of this wall assembly that still hasn't been satisfactorily resolved is the exterior sheathing. Neither fibreboard or house wraps are very good options. They don't provide a nailing base and it is difficult to maintain a rain screen cavity gap. Hopefully some better alternatives will emerge as these walls become more common.

  5. GBA Editor
    Martin Holladay | | #5

    Response to Dick Russell
    Thanks for you comment. Your detail -- installing exterior Larsen trusses, TJIs, or the exterior studs of a double-stud wall in such a way that the wall framing overhangs and covers the rim-joist area -- is a good suggestion.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Lucas Durand
    You wrote, "With all due respect to the fellows at BSC, it sometimes seems they have somewhat of an obsession with the idea of a 'one size fits all' solution to energy efficient and durable residential construction. I'm not-so-sure 'one size fits all' is that important."

    I agree. As Chairman Mao used to say, "Let a hundred flowers bloom."

    You wrote, "I don't agree that service cavities in general are some kind of cost albatross." Whether or not a service cavity is a "cost albatross" or not depends on the project's budget. What one owner might consider an albatross is just one more expense to another owner. However you want to describe the line item, however, building a service cavity costs more than omitting a service cavity.

  7. GBA Editor
    Martin Holladay | | #7

    Response to John Semmelhack
    You wrote, "There are some key differences between Larsen Truss walls and load-bearing TJI walls, but you lump them all into one category."

    It's true that I am discussing a category of walls in this article, but that doesn't mean that I am unaware of all of the variations on the theme. (For more information on Larsen trusses, for example, see my article on the topic: All About Larsen Trusses.)

    If you read this article on the Klingenberg Wall carefully, you'll see that I include a bullet list that describes many of the variations that builders have developed. I also specifically addressed the issue of making TJI walls non-load-bearing when I wrote, "If you frame a service cavity wall with 2x4s and 2x6s, you can use that wall to support the roof loads and to satisfy your building inspector. Then the I-joist wall installed on the exterior side of the service cavity wall doesn’t need to be load-bearing."

    In order to clarify the issue you raised, however, I have added another bullet point to my "variations" list, so that the issue is (I hope) less confusing to readers. Thanks for your comments on this point.

    You also wrote, "you lump them [the variations] all into one category you're calling a 'Klingenberg Wall,' though Katrin invented neither."

    I'm open to suggestions for a good name for this family of walls. My article never stated that Katrin Klingenberg invented the wall, and I specifically noted that she credited the German document, “Balloon und Platform Framing Details,” when I interviewed her about the origin of her wall system.

    Anyone who has been closely following superinsulation details and the Passivhaus movement in the U.S. for the past decade will recognize that the family of walls discussed in this article -- walls with deep cavities framed with TJIs or Larsen trusses, with vapor-open exterior sheathing and (often but not always) interior OSB -- represent a distinct category with several variations. I think that Katrin Klingenberg has done more to popularize this method of construction than anyone else in North America, but I am certainly open to considering a different name for the wall system.

  8. GBA Editor
    Martin Holladay | | #8

    Response to Malcolm Taylor
    I agree completely with your observation that neither fiberboard sheathing nor housewrap provides an entirely satisfactory solution to the exterior sheathing problem.

    There are other options, of course, including diagonal board sheathing and John Straube's approach (using OSB or plywood sheathing, and installing rigid foam or mineral wool on the exterior side of the sheathing to keep the sheathing warm).

  9. Ken Levenson | | #9

    names and options
    We (475 High Performance Building Supply) like the name "I-Joist Outrigger Assembly". It seems a simple, generic and functional name. Of course it doesn't refer to the load bearing type of wall Katrin used in her house - but as John noted, that is a different sort of wall.)

    In this case the I-joist is supporting only the insulation and siding - like a parka, hung around a 2x4 framed building (and the only sheathing is at the structural 2x4 framing). As another option the I-joists can be replaced with modified Larsen trusses. We have drawn and annotated many options in downloadable CAD DWG files. We encourage professionals to download them and edit them for their particular project needs. Here: and/or here:

  10. Expert Member
    MALCOLM TAYLOR | | #10

    Response to Martin,
    If these types of assemblies are going to make sense outside boutique green houses they need to be lean in the way conventional assemblies are. Once you have committed to placing the plywood or OSB on the interior or in the centre of the double walls, adding another complete layer of exterior sheathing is a large increase in time and materials. Similarly having already increased the depth of the wall to accommodate more insulation, protecting the exterior sheathing with mineral wool or foam on the outside is another belt and suspenders approach that is hard to justify. These alternatives work but aren't very elegant solutions to the exterior sheathing problem.

  11. GBA Editor
    Martin Holladay | | #11

    Reply to Malcolm Taylor
    I agree. This type of wall assembly is, indeed, more of a boutique-green-home method than a production-builder method.

  12. Expert Member
    MALCOLM TAYLOR | | #12

    What I forgot to add was a comment on this being yet another great synthesis of information around an interesting topic. Your blogs really are the highlight of this site.

  13. Ed_May | | #13

    Too Costly, Too Complicated, just go with Double Stud....
    Great article. But I certainly agree with most of the objections here. Using TJI's (or I-Joists if you like) is unnecessarily complicated and costly for no reason.

    The TJI's are engineered for strength across the member and do a darn good job of working in that direction. Stressing them along the axis is just fine, but they are unnecessarily strong for this application. While they perform fine as studs, in my experience Building Inspectors have wanted to see proof of this (as in, a piece of paper with actual numbers on it), which meant bringing in an engineer since most TJI load, and application tables do not have values for the member used in a vertical position. Really, you’re just paying for a bunch of engineering and strength that you simply do not need.

    In addition, Engineered I-Joists are great and flat along the tops and bottoms since they are made for floors, but can be very irregular along the sides of their top and bottom chords, this makes them very hard to work with as studs or corners or anywhere where the side of the member needs to be flat against another member.

    Along with the corners, almost all the details with these members are difficult when used as ‘studs’. How do you attach a structural header at the windows? How do I make an interior corner that receives the interior finish easily? How do you fasten to top and bottom plates? How do I make Partition studs? If you double up or get too close with two ‘studs’, you need to pre-insulate the web cavity between the doubled ‘studs’ which adds another step (and probably some foam insulation –yuck), time, and money to the framing. All of it unnecessarily complicated.

    After having done a small home with this I-Beam wall method, I can definitely say I prefer the Double-Stud wall in almost any situation. As you say, it uses existing techniques that almost all builders in this country knows, it makes the inspectors happy, it does a fantastic job of eliminating thermal bridges and can be customized to any thickness needed instead of being locked into the dimensions the I-Beam companies supply. And as Dick notes, a small change in the details at the Rim and Eave can give you easy-over-insulation of the Floor and Ceiling Joist ends. For an example, you can see some images from a double-stud wall we recently completed here:

    One extra nice thing about the double-stud and cellulose is that you can use Diagonal Bracing on the inside of the cavity (no letting in!) instead of OSB/Plywood for shear which means you can use whatever sheathing you want on the outside if your worried about it, and still forgo the oh-so-many headaches of using interior OSB.

    All in all, no reason for the expense, or the complexity. The only application this seems to make sense in would be something like Chris Corson’s wall where the beams hang off the outside and allow you to insulate the edge of a foundation slab below it. Otherwise, run with the double-stud in my opinion.

    -Ed May
    Partner, BLDGtyp

  14. user-939142 | | #14

    It's hard to do a Double Stud retrofit.

    (EIT) Exterior Insulated Truss
    seems like a good term to cover all the variants, although the slang nickname Larsen Truss will probably be what is used 20 years from now.

  15. GBA Editor
    Martin Holladay | | #15

    Response to Bob Coleman
    "Larsen truss" is not a slang nickname. It is a respectful technical term that accurately honors the inventor of the truss, John Larsen. To read my interview with John Larsen, see All About Larsen Trusses.

  16. Expert Member
    MALCOLM TAYLOR | | #16

    Question for Ed May
    Could you explain the thinking behind the hybrid foundation which uses both block and solid concrete?

  17. Ed_May | | #17

    Response to Malcolm Taylor

    Oh - that was purely an architectural decision for the visual from the exterior. The client on this project really liked the rough block-work instead of the raw concrete - felt it gave a more 'finished' look. But this is not necessary for the detail to work. You could simply pour an extra-thick foundation, or add a steel angle for a shelf, or add a wood ledger or some other blocking there to support the outer wall. The inner wall takes all the weight and the outer is sort of just 'hanging' there.

    You could also pour a thinner Conc. foundation wall and simply extend the floor joists further to the exterior to bear. So long as there is 1-2" of insulation to form the thermal break along the Rim joist it would still work fine.


  18. charles3 | | #18

    I-Joists in axial compression
    Ed May wrote, "Stressing them along the axis is just fine, but they are unnecessarily strong for this application." Are you sure about that? Years ago I asked an engineer about using I-joists to support a nonstructural ridge board over about a 19' span at a 6/12 pitch. He would not allow it.

  19. girwin | | #19

    It's about the slab edge!
    The tricky detail is thick slab edge insulation. An interior load bearing wall that rests on the edge of the slab with cantilevered TJIs over thick slab edge insulation (an EPS slab form, for example) is a very elegant solution to an otherwise quite tricky problem. Insulating beneath a slab and above it (in the walls) without addressing the slab edge in a robust manner is "expensive" in that the effort and materials expended to create a good thermal boundary are heavily bridged, in a far worse manner than a rim joist...

  20. GBA Editor
    Martin Holladay | | #20

    Response to Graham Irwin
    Of course, not all houses are built on slabs; some houses have basements. But if you are building on a slab, you're right: detailing the insulation at the slab perimeter is tricky.

    One approach is the one you suggest.

    Another approach is to install rigid foam on the exterior side of your above-grade walls; this exterior foam can end up in the same plane as the vertical foam at the slab edge.

    Needless to say, these details become only more complicated if you live in a climate with termites.

  21. doug_horgan | | #21

    Climates with termites
    Soon enough we may all be living in climates with termites!
    I recently heard that a colony has become established in Winnipeg. In that case it's an exotic invasive that relies on central heat, relatively dense housing. and a lack of termite-resistant detailing.
    However, many places that are "too cold" for termites now may not be, before the expected life of our buildings has passed.

  22. Katrin Klingenberg | | #22

    We no longer build TJI load-bearing walls
    I did not use this system on the Smith House, I was not that smart yet :)

    We started with this wall on the Fairview houses and it was an evolutionary process in regards to techniques and cost reduction. For the last version, our third 1000 sqft affordable home - the Dublin House, the additional cost for PH was 12%. That is very good for a small building in a cold climate.

    We no longer build TJI-load bearing walls for the cost reasons and doubling up functions that are mentioned in a cold climate.

    We recommend in CPHC class (and all projects you are listing here had a by us trained CPHC as a team member) to build a 2x4 wall business as usual, add OSB or plywood (its really just cost to go with OSB - the vapor diffusion of both is very similar) on the exterior of that wall, air seal (you are correct, very easy to perfectly seal including the sill and top. There we always have a physical airtight layer in the slab or in the ceiling that will be connected CONTINUOUSLY to this exterior OSB/plywood airtight layer. 100% airtight. Small 1,000 sq. ft. buildings achieve a 0.4 ACH50 easily using this method, that's an average airtightness test, most are better with this method. Foolproof, really!

    We then buy generic wooden I-beams and cantilever them (just like Chris Corson did) off of the load-bearing 2x4/structural sheathing. We do not use or recommend them as load-bearing walls any longer for the exact reasons you are mentioning: Explaining it to a code official who is not familiar is almost impossible and creates a difficult slab connection detail. The cantilevered detail brings cost down and still has the benefit of a wooden I-beam technically not being a thermal bridge (being a thermal break - less than 0.006 BTU/ft F heat loss through it).

    I personally find the double wall more prone to present airtight issues, more difficult to truly create an uninterrupted solid airtight layer, you have to coordinate two walls essentially and you still want the OSB on the exterior of the interior stud, seems more difficult to me. In addition, you are causing all kinds of load bearing trouble and continuous insulation issues once you hit your slab. But in the end its personal preference, whatever works for people as long a the hygrothermal performance is OK. Unfortunately, in many projects that come into the office for certification, people figure if double wall is OK, then plywood or OSB sheathing on the exterior of the outermost wall is also OK. It's definitely not for superinsulated walls as you make the point in your article!

    The "Klingenberg wall" that is taught during CPHC class is no "copy this sample wall detail" as you are describing here. People are taught how to modify it for mixed humid and hot climates as Joe suggests. Of course, that's how you do it. The first project certified in Arizona did use a 9.5" load bearing TJI (and here it might make sense to go back to that initial scheme, because now the exterior plywood is the uninterrupted airtight layer and smart vapor retarder and he did not need the interior installation cavity in the 2x4 layer to protect his airtight layer).

    We teach people the recipe for superinsulated walls in all climates and tell them very clearly: don't replicate the Urbana wall in Louisiana - it'll fall apart.

    Straube's comment about the "outdated thinking", well, the foam wall is an entirely different concept. I think it is a mistake to compare the two, they are distinctly different in their hygrothermal behavior, in fact (I think his answer is rather sloppy and not well thought through). My wall is the diffusion open kind and physics does not get outdated, it still holds true for this specific system. I agree, the exterior foam wall is an entirely different animal, and we teach that option as well for all climates in the US (the way it should vary by climate) to our CPHCs. Both options are fine solutions, again a matter of personal preference or other sustainability considerations.

    And now with the new WUFI Passive tool we are able to monitor the hygrothermal behavior for every project that comes into the office for certification already during the design process very closely. Designing and energy-engineering buildings is finally a science and we have the tools available to us as designers to do it right (given we know our building science).

    Exciting times!

  23. Cjb80 | | #23

    In researching this wall
    In researching this wall system that Kat described (2x4 structural framing, I-beam "outriggers"), I am having trouble finding suppliers for fiberboard. Fiberboard is apparently unused on the west-coast as there are no manufacturering gacility of the product here in the region (the closest plant that I can find that manufactures fiberboard is in Alberta). As a result, I have started to look into CDX plywood as an alternative exterior sheathing. CDX plywood seems to meet the criteria of 5x the interior sheathing permiability (assuming 0.7 perms for the OSB air barrier, 10 perms for the CDX plywood). Does this sound like a reasonable approach?

    It also seems like the the CDX plywood would not suffer from the "bellying" problem in dense pack insulation situations.

    The Agepan also looks like a great solution, but I have assumed (perhaps incorrectly) that it is very expensive; therefore, I haven't pursued that path very far. Though it does not seem to have any issues with dense packing...



  24. GBA Editor
    Martin Holladay | | #24

    Response to Chris Barnes
    According to John Straube, the permeance of plywood ranges from 0.5 perm when dry to 20 perms when wet. So it's not going to be 10 perms unless it is quite wet.

    That said, plenty of people have built thick double-stud walls with plywood sheathing. As long as you include a ventilated rainscreen gap between the sheathing and the siding, the wall should perform fine.

  25. Cjb80 | | #25

    hm, well it seems to me that
    hm, well it seems to me that the dense pack insulation would then be caught between two layers that are relatively impermiable then (i.e., interior OSB air barrier and CDX plywood exterior sheathing). If the moisture increases in the cavity, the permiability of the plywood should also increase, but perhaps it's not to the 5:1 ratio that is desired. If a rain screen fixes this problem, then I should be able to use OSB there too? I suppose another way to look at it is: Is it worth the extra $5/board for CDX plywood over OSB?


  26. GBA Editor
    Martin Holladay | | #26

    Response to Chris Barnes
    I believe that the upcharge for plywood is always worth it, unless you are building a packing crate. Damp OSB falls apart much faster than damp plywood.

    Kartrin Klingenberg's 5-to-1 rule of thumb is no more than rule of thumb. It doesn't account for summer performance of the wall, and is based on old assumptions (for example, that most homes aren't air-conditioned). You could run a WUFI simulation with plywood sheathing if you want, but WUFI simulations are subject to the "garbage in, garbage out" problem to such a high degree that WUFI results are almost always suspect and subject to debate.

    Many researchers in the building science community are now gathering data on this crucial question: "How risky are thick walls with air-permeable insulation and OSB or plywood sheathing?" Most data I've seen (as well as field experience) support the idea that (a) plywood is safer than OSB, and (b) you probably don't have to worry about plywood-sheathed thick walls as long as you include a ventilated rainscreen gap on the exterior side of your sheathing.

    Remember, if the plywood gets damp in February, it will dry quickly in April. The ventilated rainscreen gap will speed the drying rate.

  27. user-944275 | | #27

    I have done all of the walls
    I have done all of the walls talked about here, except the load bearing I joist walls, either as a designer or a builder. John Straube's exterior foam is quite easy up to a few inches of foam, then it becomes a pain in the neck screwing through all that foam--but for a "slightly better than code" house this is the way to go.

    For a truly super insulated wall in a cold climate I still find the double stud wall the easiest and most cost -effective with the HUGE caveat that it must be durable from a moisture/condensation perspective which means good design, modelling, details; possibly exterior ventilated cladding etc. I like Ed May's idea of cross-bracing instead of exterior sheathing although I don't think that would work for my seismic zone (have to talk with my engineer about that).

    BUT, Graham Irwin and John Semmelhack are right: the two huge advantages of the Klingenberg wall (which to me is the exterior I joist hung off of an interior load-bearing frame) are that:

    first, it always solves the issue of thermal bridging at the foundation, regardless of whether it is a slab or basement. With a double stud wall this is always problematic, and second the vapor retarder is automatically on the inner 1/3 of the wall, everywhere all the time. Very elegant.

  28. GBA Editor
    Martin Holladay | | #28

    Response to Dave Brach
    You wrote, "The vapor retarder is automatically on the inner 1/3 of the wall, everywhere all the time."

    True enough. But building scientists have learned that the old worries about vapor diffusion and the old rules about interior vapor retarders were based on fallacies. The main mechanisms by which moisture enters walls are (a) rain and (b) air leakage. Vapor diffusion doesn't matter.

    Moreover, the idea that you need an interior vapor retarder is a cold-climate obsession; such vapor retarders can be counterproductive in hot climates.

    For more information on these issues, see Forget Vapor Diffusion — Stop the Air Leaks!

  29. user-944275 | | #29

    the perfect wall
    Martin, you write "vapor diffusion doesn't matter". I am not quite ready to say that, and most building scientists wouldn't either. What happens when you have 5 people living in 1200 square foot air tight house and the ventilation rate is set too low to remove enough moisture?

    The beauty of the klingenberg wall (structural 2x4 with exterior larsen truss) is that the question about whether vapor diffusion matters doesn't matter, because it is so simple and fool-proof. The contractor could totally screw up the air barrier and the building would still be durable in any cold climate.

  30. GBA Editor
    Martin Holladay | | #30

    Response to Dave Brach
    Q. "What happens when you have 5 people living in 1200 square foot air tight house and the ventilation rate is set too low to remove enough moisture?"

    A. In that case, the house would have a high indoor relative humidity (RH) level. The remedy would be to increase the ventilation rate during the winter, and to use an air conditioner or dehumidifier during the summer.

    High indoor RH levels can be associated with mold and sheathing rot, so these remedies should be applied. The damage to sheathing happens because of air leakage through the envelope, not vapor diffusion. So "vapor diffusion doesn't matter," as I explained before.

  31. user-944275 | | #31

    response to Martin

    you say " The remedy would be to increase the ventilation rate during the winter,"

    True enough, at least in theory. But of course, it's never that simple. As you probably know, building occupants and operators are notoriously misinformed and unpredictable. Mechanical equipment rarely works as designed. If people are setting the ventilation rate, then you can assume it will not be set correctly.

    OK, so the ventilation system can be linked to a humidistat, which can be set to automatically keep the ventilation rate to maintain a certain relative humidity. But let's say you are an architect, energy designer, or building contractor responsible for actual building projects. Maybe you live in Maine. And let's say you need to assume a worst case scenario for a building that is being designed to last for 100 years. For those people, my advice would be: "diffusion could matter", so you might want to use the "perfect wall" because it' just more fool-proof.

    Also, increasing the ventilation rate does not make up for craftsmanship issues in the air-tight layer, which, again are inevitable for real world projects.

  32. GBA Editor
    Martin Holladay | | #32

    Response to Dave Brach
    I agree with you that it's a good idea to design a robust wall system that can handle a few construction errors and homeowner mismanagement.

    The jury is still out, however, on whether the Klingenberg wall is (as you describe it) a "perfect wall." The Klingenberg emphasis on interior vapor retarders is a little old-fashioned -- especially since so many homes are air conditioned these days.

    My own vote for the "perfect wall" would be the PERSIST wall.

  33. ethan_TFGStudio | | #33

    Rodents chewing exterior housewrap
    I see so many high performance wall details which avoid the cold sheathing problem by eliminating exterior sheathing altogether and "cladding" the exterior walls with a fancy housewrap and battens. Has there been any investigation into the proclivity of rodents to burrow into an inviting enclosure such as this? I've attached a picture of the Ecocor wall from their website ( to give a picture of what I'm talking about. Might an exterior sheathing in Gutex or Homatherm or somesuch product eliminate the rodent burrowing problem which achieving extra insulation, a thermal break, as well as a WRB? Maybe rodents will chew through wood fiberboard just as easily?

  34. GBA Editor
    Martin Holladay | | #34

    Response to Ethan T
    Good questions.

    GBA hasn't heard any reports of rodent problems in this type of wall -- but we may begin to hear about such cases in 10 or 15 years, as more of these walls are opened up during remodeling projects.

    -- Martin Holladay

  35. ethan_TFGStudio | | #35

    If a raccoon can burrow through 1x10s...
    ...I guess it can burrow through Proclima or Gutex or Homatherm. As I stare at the Ecocor wall, I guess I can see that periodic inspection of the exterior siding could at least check for large rodents...

    Maybe one of the Building Science organizations should build a bunch of boxes filled with cheese, sheathe/wrap them with various products, and then see which one the mice can claw/chew through.

    My initial paranoia about rodents led me to consider AAC (Autoclaved Aerated Concrete) but I gave up on it for the embodied energy reasons...

  36. Expert Member
    MALCOLM TAYLOR | | #36

    Does the presence of sheathing make much of a difference? Presumably, if the rodents are capable of chewing through the siding, a layer of sheathing isn't going to deter them.

    Unfortunately I have had quite a bit of experience dealing with rodent infestations. Perhaps surprisingly, one of the best deterrents is good air-sealing and insulation. Rodents aren't stupid and only expend energy if they have a good chance of success. They don't generally just walk up to a wall and start chewing. More typically they expand an existing hole or crack - and the way they know there is something worthwhile on the other side is by scent or heat.

    While almost all the older houses I've renovated show evidence of rodent infestations at some point, the new builds I've done have never had that problem. A house detailed to perform well will probably also be rodent free.

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