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Vinyl flooring supplier recommends against XPS or EPS board underlayment?

brooklynite2 | Posted in Green Products and Materials on

I’m refinishing a basement floor after some odd choices by the previous owner (eg wood flooring) led to water infiltration and mold. I am close to buying vinyl plank flooring from Cali Bamboo, and following the advice I’ve read on GBA, I’m also planning to install rigid XPS or EPS board between the slab and the vinyl. But Cali Bamboo recommended against installing the insulation, as they say it has some give and will cause the installed vinyl to be uneven.

Does the OSB on top of the foam board prevent this? I intended to install OSB as well, and perhaps just neglected to mention it to them. Or are they just flat wrong?


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  1. rsackiw | | #1

    I think you neglected to tell them, OSB over the foam should be fine. but directly on foam would be a no no.

  2. Jon_R | | #2

    With the moisture trap you are proposing, I'd avoid wood (ie, OSB). Perhaps Hardibacker?

    1. brooklynite2 | | #3

      I tore out the wood; it was glued directly to the slab and we had to get it up with a jackhammer.

      I'm planning to use Cali Bamboo's vinyl line with an IXPE padding on the bottom.

    2. PLIERS | | #5

      Jon you are suggesting foam with a backer board instead of osb then vinyl? How would that work? I know you have mentioned permeable carpet pad and rug with dehumidifier. I’m assuming you don’t like vinyl as a flooring option. Also gluing wood to the slab isnt that something that was mentioned in the article “walking the plank”

  3. Expert Member
    BILL WICHERS | | #4

    OSB on top will act just like regular subfloor, and should allow for installation of the Cali product without any issues. OSB on top of rigid foam on top of a slab will actually have less give than a "regular" OSB subfloor over joists would.

    Plywood will be a little better in terms of moisture resistance compared to OSB, and with today's crazy materials prices, there isn't much of a cost difference. I'd go with plywood. I'd also ask Cali about using their very nice "Cali Complete" underlayment between the planks and the plywood. Cali Complete is essntially very, very thin (about 1/8" thick) foil faced polyiso with an interlocking edge to let you join the sheets together. It's advantage in your application is that you can tape the Cali Complete joints (which is how they tell you to install it), and it will make a real vapor barrier to prevent anything that might grow on the slab from getting up into your living space. The downside is the Cali Complete layer will also ensure there is zero drying potential for the wood subfloor on top of the foam, which could potentially make things worse. It's something of a tradeoff -- encapsulate and risk higher mositure levels in the wood, or don't encapsulate and maybe have some musty smells. My guess is that taping the XPS or EPS sheets together is probably your best option, since that should keep musty stuff trapped beneath the foam, but the subfloor wood will still be able to dry through air flow between gaps between the vinyl planks.


    1. brooklynite2 | | #6


      Thanks, this is great. I wasn't aware of Cali Complete. Just to be clear, you're recommending the following layers, from top to bottom:

      - vinyl planks
      - Cali Complete
      - plywood
      - XPS
      - poly sheet?
      - slab

      But ultimately, you suggested going without the Cali Complete and sealing out the smells with tape. Correct? Alternatively, wouldn't 8mil poly sheeting (a layer I proposed) keep the smells from rising up?

      1. tommay | | #7

        Make sure you completely read their warranty to see all the conditions that void it......

  4. Expert Member
    BILL WICHERS | | #8

    Yep, except that I probably wouldn't use the Cali Complete with the plywood. The issue is that if the plywood stays wet, it will deteriorate with time. The taped XPS is probably enough of a barrier. Poly sheet on top of the slab might help too, but it depends on where your moisture is come from. Poly on the slab will help if your moisture is coming up from the ground beneath the slab, but if your moisture is condensing out from the air in the living space, the poly just changes which surface the water condenses on and doesn't really solve anything.

    BTW, Tom has a point -- check with the Cali people about their warranty if that is of concern to you. Part of my response about "ask Cali about ..." means see what they think of that product in that application. They might tell you it is required for the warranty -- they often recommend it's use over slabs. My expierience is that the Cali people are usually pretty helpful and easy to work with, so they'll probably be able to help you with a recommended stackup here.


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