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  1. #1
    Join Date
    Jul 2009

    Question Tar paper vapor barrier?

    My old house has a layer of tar paper between the finished siding and the sheathing. It was coated with liquid tar at every joint, all of which overlap. I plan to insulate, but wonder if the tar paper already constitutes a vapor barrier, in which case (I have learned) I would not want to put another vapor barrier on the inside, even if I could. In my climate (Wisconsin) the main concern is to stay warm in all but the summer months, so I would think a vapor barrier should be on the inside; but this is on the outside. Should it be removed? Even if I cannot put a vapor barrier behind the lath and plaster on the inside?

  2. #2
    Join Date
    Aug 2007
    The Great White North

    Default Re: Tar paper vapor barrier?

    Your tar ( or felt ) paper is not considered a vapor barrier.

    Materials having a permeable rating of 1 or lower is considered a water vapor barrier .... tar ( or felt ) paper has a permeable rating of 5 or higher which means the interior vapor within the walls will breathe outward.

    It's intended purpose is provide a barrier to protect the sheathing from liquid water also to assist with being an air barrier.

    You might consider using blown in cellulose which works fine for your application.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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