I have spray foam under the subfloor with vapor barrier. The foam is sprayed to the underside of the subfloor deck, and vapor barrier is attached to the joists bottoms between the joists and the soil in the crawlspace (converting crawlspace is not an option).

I'm going to be installing engineered wood flooring.

This install calls for an underlayment (such as floor muffler). It seems that most hardwood underlayment also includes moisture barrier.

If I use such an underlayment will that create the dreaded moisture sandwich in my subfloor deck?

  • Sorry about the lack of response here. If you arrived at a solution, please post and accept an answer. – isherwood Jun 9 at 13:08

Real hardwood flooring does not have a vapor barrier. It's just wood.

So your product is "click-flooring" type laminate ? In such a case, Yes you should check with the manufacturer (call their 800 number perhaps)

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  • Sorry for lack of clarity. They're engineered wood planks. You install an underlayment between it and the subfloor for a floating or double stick install. – Matthew Jun 4 '18 at 6:40
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    I don't think the underlayment would qualify as a vapor barrier. The underlayment I'm thinking of is 1/16-1/18" foam. – JeffFromCanada Jun 6 '18 at 4:15
  • It's advertised as "moisture barrier" but not sure if that's accurate.... – Matthew Jun 7 '18 at 5:35

In a similar situation, we floated the hardwood, removing the polythene sheet off the underlay material to avoid the double vapor barrier. Been good for 5+ years. Engineered wood flooring is the right choice in this circumstance.

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