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Vapor Retarder Over Drywall in High-Humidity Room

P Schmit | Posted in General Questions on

Hi, We are adding a room to our manuf center. Equipment requires elevated humidity. To “trap” the humidity in the room and protect the rest of the building, we are going to add vapor barrier to the wall system.

Question: if we add a vapor barrier to the exiting finish face of gyp bd sheathing, and then install another 1/2″ layer of gyp on that, will this create any issues? Are we better to remove the existing gyp bd install VB on studs and re-sheath? All walls are interior walls.

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  1. Jon R | | #1

    If you paint the existing walls with .5 perm vapor "barrier" paint and air seal, then there will be very little moisture moving through the walls. So little that it's cheap to remove with ventilation or dehumidification (depending on the season).

  2. Expert Member
    Zephyr7 | | #2

    You can sandwich a sheet of polyethylene between two layers of drywall without any problems. Where you could potentially run into trouble would be with an exterior wall, but in your case the risk of the vapor barrier there is probably less of an issue that the risk of the high humidity in the room.

    Make sure you seal the vapor barrier to the floor, and continue it over the ceiling to so that you fully enclose and seal the room. A source of makeup air then becomes important so that you maintain breathable air inside the now sealed space.


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