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Thread: Vapor/moisture Barrier

  1. #1

    Default Vapor/moisture Barrier

    I am completely remodeling my bathroom and after ripping out the old tile surround/drywall from my tub/shower I found that there was no vapor barrier behind it. After careful inspection I noticed no water damage in the walls and no moisture build up even without a barrier. If the process of redoing this area I am obvioulsy using cement backerboard and laying tile down again. Should I put in a vapor barrier this time around as well? My thought process is that if there was no water/moisture damage with drywall behind the original tiles there should be even less of an issue with a waterproof cement backerboard - any thoughts?
    Last edited by rcrowley; 04-27-2007 at 08:36 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    It takes only minutes, costs very little, and offers peace of mind (and meets code), so it is cheap insurance to do. Either plastic sheeting or roofing felt work.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    I've wondered the same thing before. However, the backer board manufacturers recomend it, every handyman book says to do it, and code calls for it so I think it is probably a good idea.

    I think part of it may be that there is more of a possibility of condensation in the wall void with the concrete backer.

  4. #4

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    I know for the little bit of extra work to put the felt up it is worth it, but seeing as it never had ot to begin with and having drywall which is not water resistant I figured putting it back up that way with cement board would be at least better than originally. Given that fact and the fact that there was no water/moisture to begin with when I ripped out the original drywall I was trying to cut corners. Call me a little lazy. For the record - if it is coce - then why did it not have some sort of vapor barrier to begin with. My house was built in 67 so could this be something that took affect after?

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    It depends somewhat on where you live, how often you use the shower, and the ventilation in the room. Moisture moves from high to low concentrations. If the wall is dry, it will get wetter. Wood doesn't like wet, so try to minimize that transfer. Condensation in a wall is not something you want. On an older house, it is likely that the house does not have a house-wrap, and probably has more air changes than a typical house that meets today's efficiency goals. This would dissipate some of that moisture before it caused problems.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Homeowner geniescience's Avatar
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    no-one can ever know in advance how much water will migrate into the space in the wall cavity. Whether or not the humidity will be so high as to let mold grow, cannot be determined in advance. Code is an organized attempt to control these factors to the point where the result is knowable in advance. Vapor barrier here is an attempt at "sufficient knowledge". Without it you'll never know. REbuilding without a vapor barrier doesn't mean that all other factors will be the same this time. Furthermore, use patterns change over the years.

    david

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