Hi all, I would appreciate your advice on choosing an underlayment for engineered wood floor (Kährs, Tres collection), installed as floating floor. I am in IECC climate zone 3B. My house is stick frame, first floor is concrete slab, second floor is (I’m presuming) plywood subfloor. Currently, first floor has laminate (there may or may not be tile underneath), second floor has carpet.

I have been told that I need a vapor barrier underlayment on first floor (concrete slab). I am also looking for additional features, including: non-toxic / low or zero VOC; cushioning; some insulation from the slab; sounds reduction.

Questions:

1) Can the same underlayment (with vapor barrier) be used on the second floor? Or should I get a different type of underlayment? I don’t know if the vapor barrier affects the wood subfloor on second floor. Is this a mold risk?

2) QuietWalk was recommended at a flooring store. But there are several models. Is this a good product? Is one model better? What thickness is good? I have read that 6mm is good, but QuietWalk says it’s 3mm.

I’m open to other product suggestions that meet these criteria. Thank you for sharing your expertise!