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Thread: Vapor barrier

  1. #1
    Join Date
    Jun 2010
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    1

    Question Vapor barrier

    My garage is stick built. I have 2x4 walls,wrapped in plywood on the outside then wrapped in house wrap and bricked. On the inside I have 3 1/2 inches of faced insulation, then wrapped in clear plastic (walls and ceiling), then drywalled. I was told this is wrong and could cause a mold problem. Is this true? Thanks for any help you could give me!

    I built the garage myself, and it is a stand alone garage, at this time it is not heated, but we are looking into that now. Thanks for all the helpful information.
    Last edited by fxrcharlie; 06-15-2010 at 08:12 AM. Reason: More information

  2. #2
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
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    Default Re: Vapor barrier

    sounds fine to me, pretty much standard construction practice, the only way the vapour barrier would cause a problem is if the space is unheated, then you really dont need the vapor barrier
    fire up the saw and make some dust

  3. #3
    Join Date
    Aug 2007
    Location
    Portland, Oregon, formerly of Chicago
    Posts
    1,808

    Default Re: Vapor barrier

    fxrcharlie,

    I am surprised at how consciencious your builder was in constructing a vapor barrier. Most humble garages would not have been so well constructed. If your exterior is completely brick, you might consider sealing the brick periodically against exterior moisture pentration which then cannot exit to the interior. Years ago I did a wallpaper removing job wear the "paper" was of water impenetrable Mylar. It was a 2 story living room. The upper wall was fine, but the lower drywall was completely soggy to where you could poke your finger through it.
    An inspection of the exterior showed that the upper walls had cedar siding and the lower portion brick. Apparently moisture was being transferred from the porous brick into the wall cavity, but the Mylar paper would not let it dry out. We had to replace the drywall and insulation. We advised the customer to start a program of sealing the brick exterior and not replacing the Mylar paper with any other moisture impenetrable wallpaper.

  4. #4
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
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    Default Re: Vapor barrier

    i forgot to ask, is the garage stand alone or is it attached to teh house. if its attached it should definitely have a vapor barrier as extra protection against fumes working their way into the house. there should also be 5/8 drywall on the walls joined to the house with a minumum of 2 coats of mud
    fire up the saw and make some dust

  5. #5
    Join Date
    Mar 2008
    Posts
    40

    Default Re: Vapor barrier

    If your insulation is "faced" do you mean it has a kraft paper vapor barrier? If so, and you added a plastic sheeting under the drywall, it sits against the kraft paper and makes a "double vapor barrier" which will trap all the moisture behind the plastic, but will foul up the insulation....

  6. #6
    Join Date
    Jan 2008
    Posts
    2,203

    Default Re: Vapor barrier

    While there should ideally be only one single vapor barrier, rarely is there a problem when a plastic vapor barrier is applied over a kraft paper insulation vapor barrier. What one does not do is have two vapor barriers located separately; one atop the other will not hurt. Why? If there is a moisture problem affecting the insulation either faced or unfaced insulation will get wet behind the plastic vapor barrier, so having a paper facing there will do no harm save that it costs a bit more than the unfaced insulation. There's a difference between unneeded and unwanted and this does practice not affect the latter. The housewrap should keep any external moisture issues at bay, and allow airflow so that the insulation stays dry and happy. \

    I too say "well done".
    Phil

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