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Caulk/adhesive for exterior sheathing to top and bottom plate

user-6258531 | Posted in Green Building Techniques on

I’ve got my box of EPDM gasket for the bottom sill to foundation wall seal. Now for the exterior sheathing. I want to seal the top and bottom plates to the sheathing. Is it necessary to use a caulk that won’t harden over time, or is construction adhesive OK? I’m planning to tape all the other exterior sheathing seams with Vycor Plus. Also looking for a recommendation on foam to use for any other penetrations to the exterior sheathing. Thanks.

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  1. user-6258531 | | #1

    Probably should have added a bit more detail. My house is new construction and is slab on grade. I'm trying to make my exterior sheathing my air barrier plane. I'll be using blown fiberglass insulation in the walls and no exterior foam board. I'll be paying special attention to the sealing for the ceiling drywall plane and any ceiling penetrations as well. I'm using flush mount led lighting, not can lights.

  2. GBA Editor
    Martin Holladay | | #2

    The brief answer is that you can use construction adhesive or any high-quality caulk. Careful installation is probably more important than the type of product you use.

    The longer answer is that the detail you use depends on your goals. A lot of Passivhaus builders have moved away from caulk, preferring high-quality tape from companies like Siga.

    To determine the best type of tape to use, and where the tape belongs, you first have to identify all of the transition points between your different air barriers. At the bottom of the wall, you are trying to seal your wall sheathing to the slab; for this purpose, you can use Siga Wigluv (which sticks to concrete).

    At the top of the wall, you are trying to have a continuous air barrier that joins your wall sheathing to your ceiling drywall. One approach is described in this article: A Practical Air-Sealing Sequence.

  3. STEPHEN SHEEHY | | #3

    Steve: We used foam from Conservation Technologies to seal various penetrations. Buy their professional foam gun and cleaner. Much easier to use than cans of Great Stuff or similar products.

  4. user-6258531 | | #4

    Thanks for the replies.

    Stephen, good tip on getting a professional foam gun. You likely saved me a lot of frustration with cans.

    Martin, I plan to caulk the sheathing to the bottom plate. There is a gasket under the bottom plate. It would seem that the taping of sheathing to the foundation would be redundant. Thanks for the article on air sealing, my next questions are likely to be how to create best seal on the ceiling plane.

  5. brp_nh | | #5

    I don't think Vycor Plus is a good choice for taping the exterior sheathing seams, I believe one of the more commonly used exterior air sealing tapes would be better: (Wigluv in either the 2" or 4")

    You could also use 3M All Weather Flashing Tape. It's less expensive, but I found the Siga Wigluv to be stronger.

    I'd second getting a foam gun (they attach to cans) and don't bother with the cans with straws.

    For other exterior sheathing'll probably find that different methods (foam, caulk, tape) work best depending on the situation. Foam can work well for bigger gaps, but sometimes caulk and/or tape works best for smaller and more detailed oriented gaps.

  6. user-6258531 | | #6

    Thanks Brian,
    Is your dislike of Vycor based on adhesion? I'll be taping plywood, not OSB. It will be summer when I tape so cold weather isn't a concern.
    My attraction to Vycor is economics. It will be a few hundred dollars less than the higher price tapes you mentioned.

  7. user-6258531 | | #7

    It appears that the Zip System flashing tape is similar in cost to the Vycor Plus. Any opinions on one versus the other for taping plywood seams? Zip seemed to do well in Martin's tape test.

  8. brp_nh | | #8

    Yes, I found the adhesion of the Vycor Plus to not be as consistently strong, especially in colder weather. I also remember it losing some adhesion at the edges after a period of time. It obviously has it's place, but for taping sheathing...I think those other options (including Zip) would probably be better.

  9. JTyler | | #9

    Steve - One other possible sollution is more EPDM gaskets. There are gaskets for plate - sheathing joints as well. Conservation technologies sells a P gasket for this application. It is stapled to the plate before sheathing is applied. Very simple and fast application.

  10. user-6258531 | | #10

    It's time to buy some polyurethane caulk/adhesive. In the Loctite family, I'm looking at either the PL Premium polyurethane adhesive or the PL S40 polyurethane window door siding sealant. I like the adhesive price and larger tubes, but am wondering if it won't remain flexible enough to flex with the building movements. I'd have the same question for the Sika family.
    This is for sealing the plywood sheathing to the top and bottom plates.
    Does it matter?

  11. Stockwell | | #11

    I have used PL Premium to build subwoofers--it is not flexible once cured, and it will never let go. The wood will give before the PL joint gives.

  12. user-6258531 | | #12

    After discussion with the folks at Loctite, I'm going to use the PL Premium Adhesive. They assured me it does retain some flexibility after cure.

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