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  1. #1
    Join Date
    Feb 2014
    Posts
    1

    Default Condensation between insulation and wall

    I have a 1920s Bungalow near the Detroit area. I've recently torn down the plaster/lath on the interior side of an exterior wall. The framing and siding is wood. I removed the blown in cellulose insulation that was there (regrettably). I have put up some pink fiberglass batts in place and am planning on covering with drywall. I've noticed that there is condensation forming between the batts and the interior side of the exterior wall. The interior side of the exterior wall looked to be orginally built with some type of black paper (similar to tar paper but not nearly as thick).

    Does this mean I need to to a better job of insulating and sealing air leaks in these locations? Adding exterior insulation is not an option.

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,472

    Default Re: Condensation between insulation and wall

    Your house exterior wrap (the black paper you mentioned) is just too old and is not doing its job efficiently. If you can't replace it, use encapsulated insulation for the walls.

    Today, if you use black paper (AKA 60 minute paper), code says to double it.

  3. #3
    Join Date
    Dec 2013
    Location
    New Hampshire
    Posts
    27

    Default Re: Condensation between insulation and wall

    The outer wall construction has nothing to do with your current condensation. In a northern area like Detroit when insulating a wall with just a vapor permeable material like fiberglass or cellulose; an air barrier and vapor retarder is needed on the inside of the insulation to prevent condensation during the winter. The drywall usually functions as the air barrier while the coated paper facing on the insulation, plastic sheeting, or a good paint job will act as the vapor retarder. Polyethylene vapor barriers are no longer recommended south of your location as they can lead to moisture problems during the summer in air conditioned buildings in hot humid locations. It's best to hang drywall as soon as possible after insulating when working during the winter. If you can't drywall right away, you could cover the wall with plastic sheeting. A layer of rigid foam to the interior of the studs will also act as an air barrier and vapor retarder if the joists are taped; and also provide significant additional insulation.

    If the condensation is really bad already you'll may want to temporarily take down the fiberglass to dry out the wall and insulation before sealing it back up.

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