I'm replacing an old LVP floor, which required an underlayment, with a new brand LVP that has an underlayment built-in. I'd think that to mitigate sound and vapor, a reasonable thing to do is to continue to use the existing ~2mm underlayment with the new floor.

But the manufacturer doesn't just say an underlayment simply isn't required, but explicitly also says that using an additional underlayment will void the warranty. I wonder if it will actually damage the flooring or if the warranty being voided is just a manufacturers way to weasel out of honoring the warranty.

Does anyone know if using a preexisting underlayment will actually somehow destroy the new LVP that has it built-in?

  • As Mike says below, too much cushion can allow excessive stress on the joints. You wouldn't put it over carpet either, for the same reason.
    – isherwood
    Sep 14 at 19:17
  • @FreeMan I probably shouldn't have said "weasel out," but I do know some manufacturers make it such that it's extremely unlikely they'll ever have to honor their warranty. While this may or may not be the case for the underlayment, you're right that I shouldn't negatively speculate. However, to respond to your suggestion, I'm not concerned about warranty at all, b/c I know they'll find a way to not honor it for another reason in all likelihood. :) Sep 14 at 19:28
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    If you want to use the other underlayment, would try a small section first and test it out Walk on it and see if it moves too much for the joints.
    – crip659
    Sep 14 at 19:39
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    I would give many manufacturers the benefit of the doubt and assume that the terms of the warranty were all "weasel out" clauses. That does not apply to all... :)
    – FreeMan
    Sep 14 at 20:02

I am installing LVP now with attached pad, additional pad will void your warranty. Anyway, you don't want too much cushion as this will affect the locking of the planks.

You can also verify through manufacturer/installation instruction as I did.

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