My installer put polyethylene between hardwood and subfloor. Is that a problem?

  • 1
    Depends on what the subfloor is, what level of the home we're talking about, what your climate is, what the flooring is.... Please revise with more detail.
    – isherwood
    May 27, 2018 at 14:25
  • sub floor is plywood - main level with framed basement- southern on ca home has an erv this is a brand new energy star home
    – Jim Drake
    May 27, 2018 at 16:16
  • Please revise to add more detail.
    – isherwood
    May 27, 2018 at 16:36
  • Is it a nail down or floating installation?
    – Jack
    May 28, 2018 at 3:31

1 Answer 1


It is a moisture barrier. See Moisture Barrier and Underlayments: Don’t Leave It Out! for a little more explanation. However, in your case that appears to have been an unnecessary expense. I doubt it would hurt anything except your wallet.

  • Given the new information in the comment above, from where are we barricading moisture, exactly?
    – isherwood
    May 27, 2018 at 16:38
  • @isherwood You are correct. Which means either (a) the installer is an idiot or (b) the installer wanted to be able to charge for installation of the moisture barrier despite the moisture barrier being effectively useless. I vote for (b), but I have become skeptical in my old age. May 27, 2018 at 16:44
  • 1
    To be fair, it's standard practice to put some sort of sheet between the layers of wood for noise abatement. Maybe that's the intention. Typically it's rosin paper, but who knows?
    – isherwood
    May 27, 2018 at 16:46
  • @isherwood Noise abatement?? What STC rating is one layer of paper?
    – Lee Sam
    May 27, 2018 at 19:44
  • 1
    I would actually ask the installer why - there could be many good reasons dreamt up. But it does sound like a waste. Did they write it up as polyethelyne on the ticket? They did the job, so they may have a solid idea.
    – noybman
    May 28, 2018 at 1:09

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