I'd appreciate advice on the best way to stiffen an exisiting 5/8" plywood subfloor on 2x10 joists.
I'm thinking of screwing down the existing plywood subfloor tightly to the joists and then topping it with sheets of 5/8" plywood subflooring laid perpendicular to the existing floor, and then I'd screw the new subfloor down into the joists too.
Would this stiffen the floor to any significant degree? Would screwing down the existing flooring stiffen it? Are there more effective (not necessarily cheaper) ways?
Incidentally, there is no access to the joists from below.
Thanks in advance for all helpful replies.