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What VB to use with wood interior walls ?

GBA Editor | Posted in Green Building Techniques on

I’m building a workshop, and I want to use either T&G wood or plywood as the interior finish wall. I’m reading that the 6mil plastic VB is now considered a bad thing, and I have no intention of installing drywall, so ADA is not an option.

What to do ?

Thanks!
(We’re in a ‘Cold’ climate, zone 5a)

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Replies

  1. wjrobinson | | #1

    Seal up your exterior tight such as the Huber Zip wall... or diy with primed seams and ice and water shield. Add your T&G. The dense pack with cellulose. Good to go.

    A million other ways.... you could put and inch of foam board on the studs, taped, then add the boards. Use fiberglass insulation if using the board foam on inside. If you have h2o handled inside and out, you should not have a problem.

    This site lets you sign up for full access for ten days... Do that and check out all their details.

    Building Science dot com has unlimited resources for free and for a fee.

  2. Chris | | #2

    Sorry - I'm confusing things with the climate zone.
    5a is my Canadian zone , closer to Northern Maine.
    Zone 5 in the US is Florida ...

  3. Riversong | | #3

    Northern Maine is climate zone 7. You must be in Canadian zone B.

    What you need is a good air barrier on the interior. You can use poly with taped seams as long as the exterior is vapor open, but make sure to seal around electric outlets and other penetrations.

    Alternatively, you can use rigid foam board as a thermal break and air barrier (with seams taped) on the interior under the wall finish. Do NOT use bituthane on the exterior, as that will be a wrong side vapor barrier.

  4. Chris | | #4

    Would 1/2" plywood with caulked seams be able to act as the air barrier on the inside ? (and double as rack bracing)

    thanks,
    chris

  5. Riversong | | #5

    Can plywood serve as interior air barrier? Sure, but I would either tape the seams with foil duct tape or use a high quality elastomeric caulk or acrylic or solvent-based urethane.

    But to better answer your questions, I would need to know:
    - whether the shop is heated
    - weather there are moisture sources in the shop
    - what the frame and cavity insulation is
    - what kind of exterior sheathing, WRB and cladding

  6. Doug McEvers | | #6

    Some of the early US Passive Houses used OSB as the primary air barrier, warm side in a cold climate. Strapped over the OSB on the inside to form a wiring chase. Seams were sealed and I would guess sealed at the top and bottom plates. I am not making the case for OSB, plywood would serve the purpose as well. The exterior sheathing was fiberboard with Tyvek and a rainscreen I believe. Along with this assembly was 16" or so of blown insulation.

  7. jklingel | | #7

    Wouldn't it be better to paint the plywood w/ an air barrier paint (as well as seal joints)?

  8. Chris | | #8

    Answers to Robert's questions:

    - shop is heated by a sun-space on the south wall, and with a small wood stove
    - shop will have a water supply, and someday, maybe even a shower!
    - at this point, the frame is still undecided, but the most likey arrangement is
    (from inside to outside)
    T&G pine board
    plywood (sealed)
    2x6 studs with ISOVER insulation
    2x3 horiz. strapping with (used) glassclad
    WRB: tyvec
    cladding: rough sawn hemlock, vertical board on batton

    I understand that the fiber glass batt insulation is not the best, but it's available at an incredibly low cost ($16 per 100 sq.ft for R25?). The alternative would be blown cellulose: $50 per 100 sq.ft for R20. (local pricing, materials only)

    The glassclad was purchased used, the original attached Tyvec is not in good shape.

  9. Riversong | | #9

    What is Isover and what is glasclad?

  10. Chris | | #10

    ISOVER is a commercial, mineral wool product, a yellow glass batt, comes in a 4ft width. The stuff I'm considering was left-over from a commerical job.

    Glassclad is a Canadian market-only product, now discontinued, which is a dense pink fiberglass board, 1.5" thick, 2'x8' sheets. originally it came with a layer of Tyvec glued on the outside. It is intended for use outside sheathing, under cladding.

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