master bedroom is lower than master bath 1 1/2" and 3/4" lower than the den. I am going to install hardwood in the den. This would make the transition 1 1/2" den to bedroom. I want to nail 3/4" plywood over existing subfloor in bedroom (then carpet) - do I need to make sure ends/edges are nailed off at joists ?
Please help..

yes, you only want to nail the new subfloor into the joists.

If you dont nail into the joists it wont be properly anchored and you may develop squeaking as the wood moves with changes in humidity and the seasons.

naile them about every 8"-10" and only into the joists.

best way it to find the joists then strike chalk lines on center and nail to them.



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