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Zone 7 home with no vapor barrier in the ceiling

Nickab | Posted in General Questions on

I am looking for advice on what to do with my home not having a vapor barrier at the ceiling. Do I need to have it? Is there a way to do it without tearing down the ceiling?

The home was built in the early 80’s in zone 7 (close to zone 6). Exterior walls are buffalo board sheathed 2×6 insulated with vapor barrier. It has a vented attic with less than 8″ of blown in insulation. There is no vapor barrier at the ceiling. We have electric baseboard heat throughout the home.

We are looking to replace windows and siding within a year. We plan to tyvek the home when we put on new siding. (I have also been thinking of adding foam zip sheathing to the exterior walls for additional insulation R value.) We would also like to add more blown insulation in the attic space for better insulation R value.

Any help or advice is appreciated. Please let me know if you need more information. Thank you.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Nick,
    There is no code requirement for your ceiling to have a vapor barrier (assuming that your attic is vented). Nor do building scientists recommend a vapor barrier in this location.

    What you need at this location is an air barrier. For more information on creating an air barrier at your ceiling, see this article: "Air Sealing an Attic."

    If for some reason you want to install a vapor retarder at your ceiling level, you can certainly use vapor retarder paint if you want. But remember: vapor retarder paint won't seal your air leaks.

  2. Jon_R | | #2

    See below for "Zone 6 and Zone 7 require a Class II (or lower) vapor retarder on the interior surface of insulation in ventilated insulated roof or attic assemblies."

    https://buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

    Agreed, vapor "barrier" paint is the easy solution.

    Blower door directed air sealing is recommended.

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