hi all, new to the forums...

i'm replacing carpet with 3/4"-thick maple. current floor structure is 2x8 joists spaced 16" o.c. with 11' span, 1/2" square edge plywood subfloor, 3/4" particleboard, then carpet and pad.

one of the sticky posts recommended laying 1/2" CDX right over the PB. but i'm removing the PB because of height differences with adjoining floors. i've removed small portions of it already, and found some water damage on the 1/2" subfloor, and definite flexing between joists.

what's the recommended way to proceed? once i'm back to the original 1/2" subfloor, can i just install a layer of 1/2" square edge cdx over it, then the maple? do i need to block the edges of the original subfloor? can i skip blocking if i add 5/8" ply or 3/4" osb instead? would the 5/8" ply need to be T&G? for the second layer (whether it's 1/2", 5/8", or 3/4") do i screw directly into the joists, basically treating the original 1/2" as a spacer?

thanks for any advice

If the damaged areas are really bad then replace those bad areas with new plywood. Then sheet with 1/2".