How low can vapor barrier go in basement

Discussion in 'Insulation and Radiant Barriers' started by qmqmqm, Mar 10, 2015.

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  1. Mar 10, 2015 #1

    qmqmqm

    qmqmqm

    qmqmqm

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    Hi everyone.

    I'm doing a small repair at home, where I plan to put back a piece of drywall and patch up the vapor barrier that was cut open.

    Just wondering how low can the vapor barrier go. Can it go all the way to the bottom of the basement wall? Or should I leave some room at the bottom for the wall to breath? It's only a small section about 3 feet across, as shown in the picture. Vapor barrier is not installed all the way to the bottom in other parts of the basement.

    Not sure if geography matters, but I live in Ontario Canada.

    Thanks in advance!

    Paul

    vapor barrier.jpg
     
  2. Mar 10, 2015 #2

    nealtw

    nealtw

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    Out here there would be venting to the outside for the cavity behind the insulation and the barrier goes right to th floor to keep house moisture out of the wall but if some has not got barrier you,re not going to win.
     
  3. Mar 10, 2015 #3

    Sparky617

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    I wouldn't use plastic in a basement. Typically the only vapor barrier used here is the craftpaper facing on fiberglass. This is a good website with details on house designs that work based on region. In a basement situation water vapor is likely to come in through the concrete block/poured concrete walls that are below grade.

    http://www.buildingscience.com/doctypes/designs-that-work/dtw-case-studies

    A good test is to tape a piece of either aluminum foil or plastic to the block wall, sealing all four edges. If water condenses between the foil/plastic and the wall you have water vapor coming through the wall. If that happens you'll have water condensing on the insulation side of the plastic.
     
  4. Mar 10, 2015 #4

    nealtw

    nealtw

    nealtw

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    Paper faced insulation is pretty much a thing of the past in Canada and ploy is the normal product to use.

    In any system that is used we have to assume that outside drainage and water proofing is good.
    Water will wick thru concrete from cold to warm, your test with plastic will prove something but what is the question. Water wicking thru concrete from cool outside to warm inside. That dosn't prove whether it it would continue or stop when the insulation is in place. It is nothing more than a salesmans trick to prove what ever it is he is selling.
     
  5. Mar 10, 2015 #5

    Sparky617

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    Check out the links to the Building Sciences site. South of the 49th Poly is not recommended below grade.
     
  6. Mar 10, 2015 #6

    nealtw

    nealtw

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    That would include most of Ontario.
     
  7. Mar 11, 2015 #7

    qmqmqm

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    Thanks for the response everyone.

    This may be a newbie question, but if I put up vapor barrier all the way to the bottom of the basement wall in that small section shown in the picture, would that cause the moisture to be trapped behind it and cause mold problems, etc.?

    Cheers,

    Paul
     
  8. Mar 11, 2015 #8

    nealtw

    nealtw

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    If you had some kind of water problem you need to be sure everything is dry before you close it up. Then there should be no problem. Thinking and proceedures change over years so with out knowing what was done and why kinda just leaves you guessing. We talk about vapour barrier but really the poly is an air barrier so electrical outlets are more of a problem for the most part.
     
  9. Mar 15, 2015 #9

    qmqmqm

    qmqmqm

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    Thanks a lot Nealtw and Sparky617!
     
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