Vapor Barrier needed for basement bathroom wall?

Discussion in 'Remodel Forum & Blog' started by mrmichaeljmoore, Mar 16, 2010.

  1. mrmichaeljmoore

    mrmichaeljmoore Member

    Jan 17, 2007
    I am doing a basement bathroom (see my other thread on my tiling saga).....

    This bathroom wil be connected to the existing finished basment area.

    My question is regarding a vapor barrier for the bathroom wall that is on the poured foundation wall....
    Do I need some plastic sheeting as a vapor/water barrier between the concrete and insulation/wall studs?

    Or am I good with just the wall, insulation and wall studs?
    Do I use just regular pink insulation with the paper on one side?

    If I need a plastic sheeting vapor barrier, how do I attach it? Where?

    Not usre if it matters, but the wall has a coat of DryLock or similar on it.....I think it was done by the previous homeowners, at least 6 years ago....

  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    You indicated you were going to use a surface waterproofing on the shower walls prior to tiling. You do not want to create a moisture 'sandwich'...IOW, you only want one vapor barrier in the wall. If you use the normal paper faced insulation, slash it after installation to compromise the vapor barrier so you only have one in the wall thickness. As to what Mapai products to use? No experience with them. I know people who have used RedGard and some of the Latticrete products, and I would expect the Mapai products are as good. The key to installation is to get the film thickness at their specified value and make sure you have no voids.
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  4. cacher_chick

    cacher_chick Test, Don't Guess!

    Jan 5, 2008
    Test, Don't Guess!
    Land of Cheese
  5. jamescorner

    jamescorner New Member

    Mar 15, 2010
    new jercy
    Spread the plastic sheet out flat on the floor. Have each assistant pick up one corner of the plastic sheet and hold it up against the studs of the wall.Attach the plastic to the wall studs with a hammer tacker or a staple gun. A hammer tacker is a very fast tool to use when installing a plastic vapor barrier.
  6. Dana

    Dana In the trades

    Jan 14, 2009
    Class-I vapor retarders have no place a basement wall assembly except in the coldest of climates. (Do you live in Manitoba?) In the US, a highly-retardent layer between conditioned space and the foundation wall drives ground moisture higher, resulting in rot potential at the sills, and spalling of the above-grade portiong of the foundation in freeze/thaw cycles.

    It's better to put XPS foam insulation between the studwall and foundation as a semi-permeable layer, which limits ground moisture transfer rates into the conditioned space, and raises the temperature of the wooden studs above the dew point. 1" of XPS is about 2 perms (a class-III vapor retarder), 2" is about 1-perm (a minimal class-II vapor retarder). In basements, anything lower than 1.0perms is pushing your luck. Poly sheeting is highly retardent at about 0.05 perms (a class-I vapor retarder.)

    Behind the tub/shower-surround you're probably better off putting in 2" of XPS between the foundation & the tile, with pressure-treated furring strips forming a ventilation gap behind the tile-backer. The more consitent vapor drive will be from ground moisture but the peak vapor drives from the tile side will be high. The gap WILL dry through the tile however, even if it isn't open at the top/bottom. If the shower use has a high duty cycle (5 showers/day) we may have to come up with a different stackupthough.

    Don't use batts with facers, only un-faced- both the studwall and (particularly the below-grade portion of) the foundation need to be able to dry toward the interior.
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