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  1. #1
    Join Date
    Oct 2007
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    Question vapor barrier sealing

    I am very confused.Someone asked about insulating a garage and the answer was to use 8" batts covered in 4-6 mil poly-vapor barrier, being sure to seal every seam. Why? would there be accidental holes punched in the poly-vapor barrier? How would you seal the holes?

  2. #2
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    Aug 2007
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    Default Re: vapor barrier sealing

    Quote Originally Posted by Airmom View Post
    would there be accidental holes punched in the poly-vapor barrier? How would you seal the holes?
    Maybe it's me but I'm confused with your question

  3. #3
    Join Date
    Oct 2007
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    Default Re: vapor barrier sealing

    Quote Originally Posted by canuk View Post
    Maybe it's me but I'm confused with your question
    I'm used to the old fiberglass insulation that was paper backed and stapled to the studs. I've seen ads for new insulation that shows covered batts. I'm guessing they are the poly covered ones. Do they come in lengths that are sealed at both ends? If you have cut to fit them in odd spaces, is that where the suggestion comes to "seal the poly barrier"? You are talking to a 77 year-old widowed grandma who will probably have to rehab an old house when I move back up North. I don't want to make any mistakes. Thanks for the reply.

  4. #4
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    Aug 2007
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    Default Re: vapor barrier sealing

    Thanks for the clarification
    Quote Originally Posted by Airmom View Post

    I'm used to the old fiberglass insulation that was paper backed and stapled to the studs.
    The paper backed bats were at one time touted as being a method for providing a vapor barrier. It's been determined those types of bat insulation are not effective for that purpose. The paper tabs that are stapled (commonly) to the studs don't provide an adequate seal preventing air to penetrate into the insulation because of the gaps between the studs and the tabs. When warm air from the home enters the insulation and mixes with the cold air inside the wall it will condense creating moisture.

    The accepted procedure is using unfaced bats placed into the stud bays ( space between the studs ) then the entire wall is covered with a continuous sheet of plastic called vapor barrier ....with all seams being taped before the wall board is installed . The vapor barrier will do two things : it will assist with preventing drafts and it will prevent the warm moist air coming in contact with the cold surface of the insulation preventing condensation.

    The same procedure will be used for the ceiling as well. When the continuous sheet of vapor barrier overlaps the walls these seams should be taped to ensure a continuous sealed envelope. There will be special attention to ensure all electrical outlets and switches , etc. on exterior walls be sealed as well.



    I've seen ads for new insulation that shows covered bats. I'm guessing they are the poly covered ones.
    Some manufacturers have started marketing fiber glass bats covered in plastic for making it easier for DIY'ers to handle it. Fiberglass insulation is very itchy causing irritation if you haven't built an immunity to it. Those that are sold with the plastic shell are not to be considered as a vapor barrier since the plastic covering has tiny holes in the plastic they are just for convenience in handling. There is usually an up charge for this and there is no performance advantage over the regular unfaced bats .


    Hopefully this helps.

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