Laminated glue down or floating? I'm assuming floating. If floating, is the cushion layer attached to the planks or do they call for the sheet cushion you roll out first? Either way, I can't think of any reason to incorporate a layer of plastic on plywood above grade. Just double and triple check every plywood seam for deflection / squeeks. I like screwing plywood down every 6-8" around perimeter and over joists like I do before inastalling Ardex GS-4.
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