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Community and Q&A

Should I tape my sheathing joints AND my rigid insulation joints?

jkarch | Posted in Energy Efficiency and Durability on

I’m designing a wall assembly which will include plywood sheathing over the studs and rigid insulation over the sheathing. Should I have my carpenter tape the joints of the plywood AND the joints of the rigid insulation, or is that overkill?

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  1. GBA Editor
    Martin Holladay | | #1

    It certainly wouldn't hurt to tape both your plywood seams and your rigid foam seams. Attention to airtightness is a good thing.

    If your budget is tight, and you can't afford to tape both layers, I would certainly tape the plywood seams.

  2. STEPHEN SHEEHY | | #2

    We taped every seam in our pretty good house. It seemed like cheap air sealing insurance. We ended up with PH level air tightness (.59ach50). Hard to say that the extra taping did the trick, but we're glad we did it. We used a lot of 3M 8067 flashing tape, with Siga tape around windows.

  3. JC72 | | #3

    Slightly off topic.

    Q: If the OP were to tape the rigid foam would she be better off using flex tape so that the tape wouldn't tear the foam as it shrinks or is even flex tape too inflexible?

  4. user-2310254 | | #4

    I taped the seams on the sheathing and foam (belt and suspenders, perhaps). Check this post for more on which tapes work best on different materials.

  5. GBA Editor
    Martin Holladay | | #6

    Q: "If the original poster were to tape the rigid foam, would she be better off using flex tape so that the tape wouldn't tear the foam as it shrinks or is even flex tape too inflexible?"

    A. For more information on rigid foam shrinkage, see Using Rigid Foam As a Water-Resistive Barrier. (The relevant paragraphs begin below the heading that reads, "Do rigid foam panels shrink?")

    The extent to which current formulations of rigid foam shrink is unknown. Rigid foam manufacturers mostly assert that today's foams aren't subject to as much shrinkage as older foams. Time will tell.

    I haven't heard of anyone using flex tape (which is expensive) to tape rigid foam seams. For advice on tapes to use for rigid foam seams, see Return to the Backyard Tape Test.

  6. jkarch | | #7

    Thank you all. That's very helpful.

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