GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Wall assembly according to Dr. Joe Lstiburek.

AzjaST | Posted in Energy Efficiency and Durability on

As stated by JL on this site back in May:
“For a custom home for a rich client – or for me if I every got really rich my air barrier would be exterior plywood sheathing with a liquid applied mesh reinforced water barrier providing continuity at joints and windows. Over that would go insulating sheathing, furring and a back vented and drained cladding (cedar siding in my case). In the cavities would go high density spray foam. Done.”
I like this idea even plywood has no way to dry if it will somehow ( but how ?) wet.
What about slight variation, from outside: cedar, rainscreen, 1′ polyiso, grace ice and water, zip panel or advantec, foam, drywall, latex paint? Certainly not production grade solution but for DIY with a lot of time and money saved on labor to be spend on better materials.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. homedesign | | #1

    I think that your solution is less affordable, less forgiving and less "Green" than Joe's

    I think that we should be looking at wall and roof assemblies that do not include Foam or Vapor Barriers.

  2. homedesign | | #2

    I think that the water barrier Joe is talking about is vapor permeable?

    and just ribbing here
    isn't 1 foot of Polyiso a lttle too thick ;--)

  3. AzjaST | | #3

    But 1 foot will be sooo warm :)
    Anyway, I don't see why my solution is less forgiving. The only differences are: insulated sheeting vs polyiso, plywood vs zip, liquid applied membrane vs grace. Not big differences just diff materials.

  4. homedesign | | #4

    Your suggestions sound less vapor permeable than Joe's

  5. user-788447 | | #5

    Your comment "I like this idea even [if the] plywood has no way to dry . . ." implies your proposal addresses the moisture prone plywood layer. Advantec/ Zip systems are coated OSB panels. My understanding is that any OSB is still more prone to moisture problems than plywood.

    I interpret Joe's "insulated sheathing" to mean rigid foam board such as polyiso.

    A wall assembly with a strategy for drying potential I think should be considered for new construction.

  6. AzjaST | | #6

    But where is drying potential in JL's wall assembly ? High density foam in cavity, liquid applied membrane on the outside plus insulated sheeting

  7. user-788447 | | #7

    I'm not endorsing Joe's proposal.
    If so much cost and environmental impact is invested in a rigid, coated plywood air barrier, why do you need high density spray foam in the cavities? Dense packed cellulose in the cavities would be my recommendation.
    A big challenge with your proposed assembly is attaching the cladding back through 1' of polyiso and also detailing and window/door openings so they are flashed properly.

  8. homedesign | | #8

    J Chesnut,
    I agree

  9. AzjaST | | #9

    I was intrigued by JL's proposal as it is totally different from one proposed by RRiversong ( boards for sheeting, cellulose in cavity). Foam on the outside will provide thermal brake. Liquid membrane or Grace provide total air and water barrier, sealing every crack and nail penetration. HD foam in cavity provide high R. Looks like there is no way that structural sheeting will get wet neither from inside nor outside, therefore no need for drying potential. Looks to good to be true. And of course, definitely not a green solution. I am not promoting any solution, nor insist it is better, just trying to learn.

  10. GBA Editor
    Martin Holladay | | #10

    If you aren't familiar with the PERSIST system, you may want to read about it:
    Getting Insulation Out of Your Walls and Ceilings

  11. user-788447 | | #11

    If you are investigating both JL's and RR's recommendations you are being exposed to all of the relevant issues.
    Other factors to consider:
    - rural or urban context, codes sometimes define the possibilities
    - who is available to do the construction, what are they comfortable with
    - regional product availability, what can you get at the lumberyards

  12. user-757117 | | #12

    Looks like there is no way that structural sheeting will get wet neither from inside nor outside, therefore no need for drying potential.

    This observation has been made before.
    Whether you think this is a good idea or not I think depends on whether you believe that the impermeable layers will remain perfect for the life of the structure.
    I think water will always find a way - buildings should be designed to fail gracefully.

  13. AzjaST | | #13

    I am familiar with PERSIST and while interesting from building science point of view it is ( for me) "esthetically challenged": wall is almost 1foot thick and windows, no matter outies or innies, are not attractive. So I am looking for perfect cold climate solution in standard size, wall max 6 " thick. But the more I read, I am less and less assure what to do.

  14. homedesign | | #14

    I too have been tempted by "the perfect wall"
    be careful
    the force is strong

  15. Riversong | | #15

    Time for the other side of the equation to chime in.

    Looks like there is no way that structural sheeting will get wet neither from inside nor outside, therefore no need for drying potential.

    Don't forget Murphey's Slaw (the cole slaw that will always leave you bellyaching). If you believe in perpetual perfection, then you're a prime target for Murphy.

    Looks to good to be true.

    If it looks to good to be true, you can be sure it ain't.

    And of course, definitely not a green solution.

    Shouldn't this be enough of a reason?

  16. Riversong | | #16


  17. wjrobinson | | #17

    PRZEMYSLAW BUREK check out Amaris Home in Minnesota..... Looks like they have a closed cell foam non green spec home wall that is really performing well for them.

    For a wall outsulated with foam sheeting... check our what Bruce Brownell builds..

    Note: Foam insulations are not green products themselves. To go totally green is to use cellulose and straw bale and to not have children.

  18. Brett Moyer | | #18


    Your sarcasm is a week attempt at humor.

    We all know you pimp spray foam.

  19. homedesign | | #19

    What is YOUR climate Zone?

  20. wjrobinson | | #20

    Brett. No way Brett. How in hell do you figure? Around me, the only homes of any quantity that use way less E use foam. It seals, and in sheeting aspects it delivers whole wall R value simply and elegantly. I am a firm proponent of Cellulose double walls though for those including myself (!!!) that want to be as green as can be in the year 2011.

    As has been mentioned, here at RPI, they came up with mushroom based foam and are working hard to get it to market. I absolutely love this product and work for the PHD who guided this idea coming about. I knew about it before I could talk about it even.

    I pimp foam for where it does a job. I pimp cellulose for where it does a job.

    And I am not sarcastic at all or at least was not trying to be.. just trying to head off posts like yours coming in to set fire to me! LOL.

    As to kids... the day is coming when the big curve up in pop.. will have to curve back. It's quite clear we all need to stop reproducing till we get back to sustainable numbers. Well we don't have to... one way or another water does level out... and this bump in pop. will too.

    Brett, I hear your angst with me... what am I saying via these two posts that is different than your thinking so we can somehow have a meeting of the minds at least?

  21. wjrobinson | | #21

    Engineering 101 electric lab... Professor Baker... Baker's Law on day one.. the chalk board, (we had chalk boards and slide rules though and the first HP scientific calculators (with reverse polish logic no less... (what is that?))(means, no parenthesis needed (like I am using here)))

    OH... so... on the chalk board... was...

    Bakers Law... Murphy's Law is always right.

  22. Riversong | | #22

    Actually, it's perfectly green to have up to two children as long as both parents kill themselves before the kids are born ;-)

  23. PBurek | | #23

    To John Brooks
    My zone is: DFa or 5

  24. Riversong | | #24

    My zone:

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |