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Community and Q&A

Basement ceiling

deb | Posted in GBA Pro Help on

I’ve put insulation between my joists, and just was told, I put them in upside down. Apparently, the paper should face the floor above.
Would just slicing the paper suffice or should it all be turned around.


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  1. GBA Editor
    Martin Holladay | | #1

    It really doesn't matter very much which way the kraft paper faces in that particular application. The "correct" way would have been to install the kraft face upwards, but it's not worth worrying about now that the job is over.

    In general, fiberglass batts are the worst possible insulation. If you want to improve the R-value of your floor assembly, you can install a continuous layer of foil-faced polyisocyanurate (rigid foam) on the underside of your floor joists.

    I'm confused, however. In another thread (Basement wall insulation) you told us that you have already insulated your basement walls. If you did, then there really is no reason to insulate your basement ceiling.

  2. Expert Member
    Dana Dorsett | | #2

    Slicing batt facers does next-to-nothing for changing the moisture diffusion, which is a total surface-area type of deal. It does ruin any air-sealing function the facers might provide though.

    Unless your basement runs VERY cold (literally near-freezing for weeks or months) it's unlikely that you'll end up with condensation on the fiber side of the facer. Leave them alone- the facer helps contain loose bits of microfiber that can otherwise become an indoor-air quality problem.

    But x2 on insulating the foundation walls. In very cold areas with a cold/very cold basement due to high-R on the basement ceiling failing to insulate the basement could even lead to frost heaving the foundation or basement slab. (That's not a real issue for 99% of the lower 48 of the US unless you literally leave the basement windows open and let it freeze hard.)

  3. deb | | #3

    I'm using this area of the basement as a woodworking shop. I thought using the insulation would muffle some of the noise. I had gotten about 300 2x2 tiles for @$100 and was going to nail up thin ledger boards and cut the tiles to fit. This way I could remove them to access wire and pipes.
    I thought the space between the insulation and the tiles would help with the noise.

  4. Expert Member
    Dana Dorsett | | #4

    The batts will definitely reduce noise transmission between the basement & first floor, but the gap is the least of it. Ideally the batts would be snugged up to the subfloor (hopefully this is the case?) If there is a channel of air between the fiberglass and subfloor that provides a thermal-bypass for infiltration currents, reducing the effectiveness of the insulation. It'll dampen sound about the same either way.

  5. deb | | #5

    Thanks for all the info, and saving me a lot of time, money and effort.

  6. wjrobinson | | #6

    Dana, Martin too, Joe L says floor insulation best not to be in contact with floor. You three and me and the world need to be on the same page. So what page? I side with Joe till ya convince me otherwise.

  7. Steve95065 | | #7

    Everyone here is missing another very important point. On the paper facing of the insulation is a great big admonition that reads something like "This paper facing will burn and must never be left exposed and must be installed in substantial contact with finished surface". This is a code issue. Everyone worries about spray foam being exposed but seem to ignore that the building code, and the insulation itself say not to leave the paper exposed.

  8. GBA Editor
    Martin Holladay | | #8

    Good point. I was assuming that the ceiling would be covered with drywall. If it isn't, then the exposed paper is a definite no-no.

  9. Expert Member
    Dana Dorsett | | #9

    AJ, if you're still reading this thread, what's JoeL's stated rationale?

    This is news to me. Radiant floor guys are forever snugging up R19s to the subfloors to avoid thermal bypass currents from robbing performance.

  10. LucyRHarmon | | #10

    Thanks for sharing this info

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