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Bathrooms and Vapor Barriers

| Posted in Construction Techniques on April 10, 2005 05:50am

 

We’re renovating an existing bathroom in our 1920 bungalow and we’ve installed a vapor barrier on all the walls. We’re also installing a ceiling fan to take care of the moisture. However, we have friends who’ve told us that it’s wrong to install a vapor barrier in a bathroom, as it makes more sense to allow the water vapor to migrate through the walls.  I don’t think it’s appropriate to let the water vapor migrate through the exterior wall where it will condense on the exterior sheathing on the inside of the wall in the winter.  However, it sort of makes sense on the interior walls, though it still sounds counterintuitive to me. Does anyone have any experience or knowledge in regards to this? Thanks.

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  1. luckypenny | Apr 10, 2005 07:09pm | #1

    Tiberia,

    I'd never heard of not installing a moisture/vapour barrier until recently and I don't know where that idea came from.

    For more info on bathrooms and tiling you should also check out the discussion forum and learning pages at the Ontario Tile Setters web page. http://www.ontariotile.com

    Live light enough to see the humour and long enough to see change.

    -Ani DiFranco

  2. Hubedube | Apr 11, 2005 03:25am | #2

    Normally, a vapor barrier is installed on the heated side of the wall (next to the drywall.)

    Exterior walls only.

    1. Tiberia | Apr 11, 2005 07:07am | #3

      The intention was to keep bathroom moisture inside the bathroom so that it could be vented through the ceiling fan that we'll put in.  My friends' advice was that if the vapor barrier is there, moisture will get trapped between the drywall/ backer board and vapor barrier, causing rot.  However, I don't want moisture migrating to the exterior wall where it will definitely condense and sit in the cavity.  On the interior walls, I suppose I should have nixed the barrier and let the water vapor migrate through, but I was concerned that again the vapor would have condensed  in the wall.  After thinking about it, I would guess that a ceiling fan on a timer and our slightly leaky window will take care of most if not all of our water vapor.  Any thoughts out there?

      1. dIrishInMe | Apr 11, 2005 02:34pm | #4

        When you say "vapor barrier" do you mean sheet polyethelene or what?

        In my area, (mid-south-east US) plastic vapor barriers are somewhat "out of vogue" because of fears of moisture buildup and possible asociated mold issues.  I think they still use them a lot "up north "though.  I wouldn't worry about it too much, but also, I don't know what area you are located in.

        You said "ceiling fan".  Not sure what you meant by ceiling fan, but the most important item for moisture control in a bathroom or kitchen is a adequately sized exhaust fan that blows the moist air to the exterior of the home.  An 80 CFM is good for most smaller baths.  FYI, the full bath and kitchen are sometimes refered to as "moisture point load areas" by building scientists.

        BTW - I don't think you have to worry about your backer board rotting though :-) Matt

        1. Tiberia | Apr 12, 2005 04:55am | #5

          Yes, I meant to say polyethylene vapor barrier.  Also, I had meant to say that it was an exhaust fan, not a ceiling fan. 

          1. chocolatehills | Apr 12, 2005 08:44am | #6

            I am not sure what you are worrying about but drywall with a primer coat and 2 layers of latex paint is an effective vapor barrier and passes some code requirements. Makes sense too. behind any tile you should use something else for a water barrier (like building felt).

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