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  1. #1
    Join Date
    Feb 2008

    Question Vapour Barrier Confusion

    [Excuse the British spelling ]

    I'm back for more advice from the TOH gurus

    We have an old 1914 home in Seattle. About once a year, during very heavy rain, our basement would take on up to 1-2" of water in one low-spot. The concrete walls never got wet, and so it appeared to be a water-table issue. There are small traces of effervescence but I have never seen moisture on the walls.

    We had a basement waterproofing company come and install interior French drains. As part of their installation method, they insert a dimpled plastic barrier against the walls as shown in this photo:

    The idea is that if moisture comes in from the outside, it hits the plastic and drains down into the French drains. Normally, they rivet the same material all the way up the wall to above the dirt-line. We didn't do that bit – and it's way more expensive to have them come back and do it.

    I'm looking at using spray-foam insulation as it has the advantage of obtaining R21 in a 2x4 cavity (vs. 2x6 for fiberglass). I'm getting conflicting messages from insulation companies.

    1. Aqueous Basement Systems suggest that I install 6mm plastic sheeting on the concrete and tuck it into the plastic dimples – so that if moisture enters from the outside, it has a place to run. They can spray open or closed cell foam onto the plastic in-between studs. Makes sense to me.

    I know that most vapor barriers (or "retarders") are installed on the "warm side in winter". So I assume I would ALSO install an additional barrier on the dry wall side. Something like this "smart barrier" looks interesting. Which changes its permeability with humidity.

    2. Burnham Insulation strongly advise AGAINST a vapor barrier on the concrete side – saying that it could cause moisture to be come trapped in the insulation and have no way to breathe. Interestingly, they also only recommend closed-cell foam for the Pacific Northwest – claiming that the open-cell shrinks over time and so doesn't not fully fill the cavities.

    3. To confuse things further, this excellent article, cited by previous posts: suggests there should be no dry-wall side barrier: "The best insulations to use are foam based and should allow the foundation wall assembly to dry inwards". However, I'm not sure if Seattle qualifies as a "cold climate".

    So what do I do? Install a drywall-side barrier? Also install a concrete-side one to channel foundation leaks into the drains?

    Pointers much appreciated - I know that this issue has been discussed a TON of times - but I'm having a hard problem deciding which advice is region-specific as there is such a diverse geographical group on the forums.

    Confused and bemused,
    Last edited by brettmarl; 05-22-2008 at 12:20 AM. Reason: typos

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