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Wall Assembly Options for Zone 6

Wiscoguy | Posted in General Questions on

Ok guys I have it narrowed down to two different wall assemblies that I am considering both have there pluses and minuses.

So wall one is a 2×4 wall with rockwool r15 inside and a smart vapor barrier before drywall, zip sheeting taped and sealed. Then 4” of polyiso foam on the outside to get me to about an r35. This system would only breathe to the inside but I should have enough exterior foam that the sheeting should never get cold. This wall assembly is easier to fur out because of less compression vs wall system 2 but it’s not as vapor open.

wall 2 is a 2×6 wall with rockwool r23 smart membrane before drywall then plywood or osb with delta sa for a more vapor open concept and 3” of rockwool outside to get me close to r35 outside. Positives are rockwool is vapor open and should breathe better allowing for drying of the wall assembly both ways. However I’m not getting the same insulation value on the outside which could create a problem with the wall sweating because I have more insulation inside. Also rockwool does compress and the rain screen will be a little more difficult to attach and keep straight.

I live in  south east Wisconsin zone 6 these are the assemblies I’m comfortable with doing that I can afford and do most of, if not all of it, myself.

I would greatly appreciate anyone else’s feedback or experiences with either of these assemblies and what your thoughts are in dealing with my climate and these two different wall assemblies. In my mind I’m not sure that the vapor open overrides the fact that there’s less exterior insulation.

Using quality windows and doors probably Duxton.

please help me out here I’ve gotten some great info so far here this is my final step I’m about to start sending everything out for bid.

thanks everyone

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Replies

  1. Expert Member
    PETER G ENGLE PE | | #1

    #1 will be easier to build and probably a bit cheaper. Have you investigated using recycled EPS foam for the exterior? Not quite a high R-value, but not bad when you derate the polyiso for temperature. And, it's a little bit vapor permeable. Recycled is cheaper than new and the big advantage is zero current carbon cost. Search Craig's list in your area to see if there is any available.

    1. johngfc | | #6

      Peter - is there a way to tape or otherwise seal seams of used iso with the fuzzy fiberglass facing?

  2. charlie_sullivan | | #2

    An option to consider on #1 is two inches of polyiso right on the sheathing and then two inches of EPS outboard, because the EPS won't drop in R-value at low temperatures. If you don't find reclaimed EPS, you could go with graphic EPS to get R-5/inch instead of R4.

    #2 is also viable.

    1. Wiscoguy | | #3

      Is version 2 going to have moisture issues even though it’s still vapor open on both sides

  3. Wiscoguy | | #4

    Anyone else have any thoughts on the two wall assemblies and which one may be better for my climate. Appreciate any more opinions

  4. rocket190 | | #5

    I’m following this thread. Have you had any luck finding a contractor to do this work, or are you doing the siding and exterior trim yourself?

    I am planning a house and keep waffling between different wall designs. I know framers in my area are so busy that they’ll either pass on the job or bid it extremely high, so I was leaning toward doing zipR with batten rain screen andditional interior spray foam. then fiberglass bibs to fill the cavity after rough ins. That would make the rest of the build pretty standard.

    1. Wiscoguy | | #7

      Seeing how I’m a contractor and so is my dad I have a lot of friends and people that will help me build my house for next to nothing however I’m still unsure about exact wall assembly I really like the rockwool approach to leave it vapor open as much as possible but I’d love to get some more feedback on this kind of setup.

      Most everyone Enid very busy right now and you are correct to assume any builder not familiar with the style of building you are trying to do would be problematic because they just see it taking twice as long and to be honest if they aren’t use to the process it may.

  5. maine_tyler | | #8

    Wiscoguy,

    As you probably know, your wall version 2 has exterior R to total R ratio of about 34%. With foam in zone 6 the target is 36%. So the question is: are you close enough given the drying potential of mineral wool?
    I won't 'answer' in any definitive way, but my instinct says, 'yes.' You are very close to the correct ratio to begin with, and you have the advantage of drying through the mineral wool. Just don't do anything to block up that drying path (such as with siding or other low perm membranes). Interior smart retarders also help you here.

    If you felt uneasy about it, you could go with plywood sheathing instead of osb, which has better vapor pass-through.

    None of this is to say wall 2 is better than wall 1, but that I think you're probably safe building it.
    You could also look into rigid wood fiber-board (steico/gutex). Right now, given that it's imported, it probably doesn't price out, but my impression is that it's more friendly to work with than mineral wool due to being stiffer and cutting like a wood product.

    1. Wiscoguy | | #9

      I could always go with more exterior rockwool to

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