I am preping for an install into multiple rooms that had both tile and carpet previously. The tile was on 1/2" BCX, but I am tearing it all out in the removal process. I have 3/4" T&G as a subfloor. The 1/2" was nailed and glued with construction adhesive previously. So hear are my questions.

1.) When putting down the new 1/2" plywood underlayment, should it be glued (with construction adhesive as before) as well as nailed to the subfloor? It seems to me this just creates spots of good contact and spots that are slightly hollow without full glue coverage unless a trowelled on application is used.

2.) There are several low spots in the floor I plan to level using the tar paper layering technique described here. Is there any advantage to disadvantage to leveling the sub floor first then covering over the paper shims with the 1/2" ply, or does the paper really need to be on top.

Thanks,
HJ