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Community and Q&A

Using 1/4” Sheetrock as Air Barrier for T&G Ceiling

David Smith | Posted in General Questions on

In my log-walled home, I am removing a drywall ceiling in a bedroom that has water damage from an old leaky roof that has since been replaced. I am planning to install whitewashed T&G pine and my original plan was to do so with a roll of paper air barrier, but after reading several posts on this site it seems that is not recommended due to nail hole penetration and that Sheetrock is the most recommended air barrier. The way that the ceilings are currently installed is that the Sheetrock tucks over the top of the log walls where there is a 1” plate separating the top log from the rafters. I would prefer to keep this style as it has the cleanest look where the ceiling meets the log (rather than butting the ceiling against the side of the log). Because I only have 1” of space for ceiling material, can I use 1/4” Sheetrock for the air barrier seeing as it will be covered with 3/4” T&G pine, nailed through the Sheetrock into the rafters?

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Replies

  1. Expert Member
    Michael Maines | | #1

    David, while some members of this site don't like membranes as air control layers, in my experience, with the right product selection they work fine and are easier to install than rigid materials. In particular I like Pro Clima Intello and Siga Majrex.

    Have you ever tried to install 1/4" drywall overhead? I have not, but 1/2" is floppy enough that I think you'll find 1/4" nearly impossible to install well, and it will sag between joists making it hard to tape properly, a requirement for it to be an air control layer.

    1. David Smith | | #2

      Michael, thank you for the reply. Exactly the kind of info I was searching for. I have not tried to install 1/4” drywall; only 1/2”, but I imagine you are correct about the installation difficulty.
      Thanks for the material suggestions. I will look into those.

  2. Expert Member
    Akos | | #3

    No for the 1/4 drywall. Next to impossible to hang on a ceiling, way to soft.

    Definitely one of the fancier membranes will work but you can also use standard 6mil poly. Get the widest roll you can get so there are no or only a few seams. Make sure the seams are parallel to your rafters, this makes taping the seam much easier. Caulk around the perimeter and at all seams followed up with a quality tape.

    My cottage has this for ceiling, I'm not going to say that is is passive house air tight, but definitely not drafty.

    You can also go with 5/8 T&G and 1/2" drywall/osb/rigid insulation. Rigid insulation in this case would be much easier to deal with overhead than a membrane or drywall. It would only be slightly thicker than what you propose but definitely more robust.

    1. David Smith | | #4

      Thanks, Akos. Two rooms in my house use the poly membrane with T&G and that was my first thought when I decided to do this, but I read it was a vapor barrier and that could cause condensation on the attic side. Maybe it works ok because I’m in a very dry climate, but because I have the time and will be exposing the rafters anyway, I wanted to avoid anything that might cause further issues later.

      I like the rigid insulation idea. I’m going to do some research on that as well.

      1. Expert Member
        Zephyr7 | | #5

        You shouldn’t have a condensation issue with poly on the ceiling if the ceiling is the floor of a vented attic. You can have issues with condensation if the poly is on the cold side of an assembly, but usually the issue with poly is that it prevents drying and can allow moisture issues within a wall. Ceilings are different, since the attic space is generally not sealed and always allows for drying as a result.

        Bill

        1. David Smith | | #6

          Bill, thanks for the clarification. Is there any risk of moisture building up within the attic insulation? In this scenario, there would be poly attached to the underside of the rafters and the rafter bays are currently filled partially with loose mineral wool, overlain with fiberglass batts, but I am considering replacing it all with cellulose in the future.

          1. Expert Member
            Michael Maines | | #7

            David, you didn't mention your climate zone but a well-ventilated attic is the one location in temperate zones where polyethylene is reasonably safe from moisture accumulation. For a bit more cost, variable permeance membranes are still safer. Whether the cost savings is worth a bit of added risk is hard to say. For me it's not worth it, but it's your house.

  3. David Smith | | #8

    Michael, I'm basically in Zone 7 in Colorado (although the county is technically Zone 5, I'm on the county line between a 5 and 7). Like I stated earlier, half of the house has original T&G with poly backing and although I haven't inspected the attic thoroughly, I have not noticed rot or mold up there and I know there is air infiltration into the attic during the winter because the old can lights are leaky and need to be replaced. Anyway, after reading your comments, I am more comfortable with the poly and may end up going that route.

    I bought the T&G yesterday and will be stacking it with stickers today to acclimate. Anyone have a recommendation for how many days, or should I just get a moisture meter?

    I appreciate all of your advice.

    1. Expert Member
      Michael Maines | | #10

      David, it sounds like you should be safe, then. There are various rules of thumb for acclimating but the only way to be precise is to use a moisture meter.

  4. David Smith | | #9

    Also, yes the attic is thoroughly ventilated: full length soffit vents on eave eave with baffles to keep the insulation off them and a full length ridge vent.

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