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Thread: mysterious basement water

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    DIY Junior Member Robert Dawn's Avatar
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    Default mysterious basement water

    HI, I wanted to mention a problem I have in my basement that has me baffled. I bought a 6 year old home recently, (and I had a home inspection done) and it is a 2 storey w/unfinished basement. The basement actually has an open ceiling, showing all plumbing and electrical, as well as joist construction(engineered). When I bought the home, the basement walls were framed over the concrete(floating) and had fiberglass insulation installed between the studs at 24" centers(non bearing, just built obviously to hold whatever covering that was to be put on the walls). The wall was covered with a vapour barrier which was glued to the studs with some black adhesive type crap. I have previously renovated 1/2 of the basement w/drywall 1/2", and laminate on the floors. Now 3 weeks ago I started the other half and just finished painting the drywall and the NEXT day, I see water pooled against a wall( really only about 1-2 litres, and the floor under the drywall is wet for 10 feet in 2 directions. The basement hasn't leaked prior except on 1 bad rain storm that blew so hard that it pushed water through my window area around my sill plate. This time I found the leak, there was snow piled up on my doorstep and it got very mild that day and I think water leaked around my siding somewhere. I moved the snow and hadnt seen anything since as the next day was mild also. There is also a window in that area and I only have a screen covering it on the exterior. I was here last year and no leaks. Anyone have a suggestion where I can start to look before ripping drywall? Is there something Im doing wrong( other than using fiberglass insul. in the basement). BTW as I have the open ceiling, I can move the batt insulation away from the wall above the basement framing and I can see that there is light frost on the plywwod sheathing above the sill and the top of the basement wall is frosty also. Thanks

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    It sounds like you have trapped the cool air behind your new drywall and you are getting condensation. There should be no vapor barrier in a basement, because the moisture in the walls must be able to dry to the inside. Any fiberglass insulation in there will absorb water, which is not the direction you want to go.

    There is a good article for you to study here- http://www.buildingscience.com/docum...lation-systems

    I don't think there will be a lot of posts today because of the holiday, but there are a couple of experts here on the forum who will be likely to chime in eventually.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I looked at a home yesterday with wet carpets in the basement by a window.
    Looking outside, the window was submerged slightly, or at least the wood framing for it by the garden outside, that had been tilted toward the house. The day before had been record rains with wind blowing from the South, pelting that side of the home.
    Pulling the dirt away from the window, and changing the landscaping to grade "away" from the home would have helped.
    Anytime you have water and wood, the wood can wick the water up.

  4. #4
    In the trades Dana's Avatar
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    Quote Originally Posted by cacher_chick View Post
    It sounds like you have trapped the cool air behind your new drywall and you are getting condensation. There should be no vapor barrier in a basement, because the moisture in the walls must be able to dry to the inside. Any fiberglass insulation in there will absorb water, which is not the direction you want to go.

    There is a good article for you to study here- http://www.buildingscience.com/docum...lation-systems

    I don't think there will be a lot of posts today because of the holiday, but there are a couple of experts here on the forum who will be likely to chime in eventually.
    Unless there was gale force winds pulling 75%RH water from the house into the cavity you'd never see several liters of condensation in that time frame. This is definitely a bulk-water issue, and the solution is to keep all snow/water away from contact with the outside of the house, via roof overhangs/gutters/surface drains- whatever it takes.

    Even though it's required by code in B.C. interior poly vapor barriers on a basement studwall are a TERRIBLE idea for maritime climate. In that climate (unless you live in a high mountain pass), with 2x4 framing even R3 foam separating the walls from the studs would be sufficient exterior-R to keep the studs from adsorbing water over the winter without ANY interior vapor retarder (not even kraft paper) as long as the gypsum is reasonably air tight and painted with standard latex paint. With that sort of wall assembly the occasional bulk-water intrusion has a chance of drying rapidly without creating mold and rot issues with the studwall. But with interior poly it's trapping groundwater moisture and rain/dew accumulation in the concrete in the studwall space, almost guaranteed to have mold issues at some point.

    Fiberglass & rockwool in the studwall are fine, as long as there's a path for drying toward the interior. Otherwise your only real options are closed cell foam (EPS or XPS, or spray polyurethane), but not in the stud-bays, but rather between the (moisture laden) foundation and the studs or furring holding up the gypsum.

    If you rip it out and start over, put an inch of EPS or XPS under the stud plate as a capillary break from the slab too. R4 (25mm) EPS is probably the cheapest way out on the foam, and the greenest (since it is blown with pentane rather than HFCs, with less than 1% of the greenhouse gas potential of XPS or closed cell spray polyurethane.) Seal the seams with 1-part foam or duct mastic. Then, insulating with R13-R15 unfaced fiberglass or rockwool between the studs would bring the wall performance up to that of standard 2x6 construction. You may be able to re-use the fiberglass and studs if you deconstruct it before mold sets in. Fiberglass dries pretty quickly.

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