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Community and Q&A

Vapor Barrier placed under EPS – Need to fix?

Jay M| Posted inGeneral Questionson

Hi GBA Community,
Prepping for a basement concrete radiant slab install and the vapor barrier was placed under the layer of EPS.

12″ Gravel – 15 Mil VB – EPS – 10 Gauge Wire Mesh – Pex

Is this a major cause for concern? I’m reading that this may cause the slab to take longer to dry. Is this the only bad thing about the VB under the EPS? Should I worry about anything else? I obviously would need to weigh this against re-working the assembly.

Thanks,
Jason

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Replies

  1. Expert Member
    Michael Maines||#1

    In some cases the foam could float, but if you keep the water ratio relatively low it should be fine.

  2. Expert Member
    Malcolm Taylor||#2

    JMrtns,

    If the rebar or mesh isn't down yet, you could alway lay another layer of 6 mil poly over the foam.
    Ads Michael said - what you have isn't ideal, but it isn't the end of the world either.

    1. Jay M||#3

      Thanks Malcom and Michael for getting back to me. I forgot to mention two things that may help:

      - All the insulation seams were taped to hopefully avoid the float (although a 6 mil poly probably would have been easier/cheaper)

      - We don't plan on finishing the basement for at a least a couple of years. This should allow enough time to dry, right?

      1. Expert Member
        Malcolm Taylor||#4

        It may not be the right way to do it but it's very common and doesn't seem to lead to any big problems. Given your circumstances I wouldn't worry about it.

      2. Expert Member
        Michael Maines||#6

        I do know of one example where the foam floated but they weren't expecting it and it caught them by surprise. With taped seams and a dry mix you should be fine; just keep an eye on it. If you want to sleep better you could add another layer of 6 mil poly. I probably wouldn't.

  3. Chris Jorgensen||#5

    We did it that way 11 years ago with no problems.

    Chris

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