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Showerthought: the old 'floating floor' trick for concrete slabs is basically wrong now
I was reading a building science paper from the University of Minnesota last night... it said that putting a vapor barrier directly on a slab before a floating floor can trap moisture and cause mold in over 40% of cases in certain climates. I've been doing it that way for a decade because that's how I was taught. The paper said you need a specific type of breathable underlayment instead in a lot of older homes. Has anyone else run into this and switched up their method?
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hayes.joel15d ago
Honestly the whole "breathable pad" thing feels like a solution looking for a problem. Mitchell mentioned that nasty job with mold, but that sounds more like a serious slab leak or a drainage issue, not a standard vapor barrier failing. Most slabs are plenty dry, and that plastic sheet has worked fine for millions of homes for decades. Switching to a fancy felt pad seems like an overreaction to a few bad cases, and it probably costs more for no real gain in a normal situation.
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mitchell.lee15d ago
Yeah that paper lines up with some nasty jobs I've seen. Had to pull up a laminate floor last year where the pad was basically glued to the slab with black mold. The homeowner had used a standard plastic sheet barrier because the store clerk said to. In that older house, the slab was always a little damp from the ground. The new breathable pads feel almost like a thick felt and let that tiny amount of moisture pass through to the room air instead of trapping it. Makes you wonder what other old standards are quietly causing problems.
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