I've seen many variations of my situation discussed here, but I'm new to all of this and I want to make sure my plan is sound.
I'm finishing a bonus room over the garage that currently has only a 1/2" plywood subfloor. That's too thin, so I need to install a 3/4" inch plywood underlayment on top of it. (There will then be LVP flooring on top of that.)
One unusual twist: because of the arrangement of the stairs, it is impossible to get a full-size 4x8 plywood sheet to the room. So the 3/4" plywood is all in 4x4 half-sheets.
From what I've read, it sounds like my approach should be to offset the underlayment so none of the edges line up with the edges of the subfloor sheets. (There's no question of whether the sheets will be perpendicular to the joists, because they're square.) I will use adhesive and screws to secure the underlayment to the subfloor (but the screws will not reach into the joists).
One question: since I'm not attaching the underlayment to the joists, I am a little unclear on exactly where the screws should go. Around the edges, obviously; but where should I place screws in the field? Just evenly spaced (i.e. in an eight-inch grid) throughout?
Anything else I've failed to consider?