So shown below is a picture of the current state of my floor after stripping the carpet and some weird old vinyl tile. I'm am going to be putting carpet over it, but first I want to sure up any squeaks and fix the hole shown. The hole is pretty small but looking through it extends all the way to the plaster ceiling below. I'm assuming there is a subfloor below that is also chipped away since the planks are staggered that means there must be a difference layer below- is this correct? This house is about 70 years old- what would be a typical subfloor type for a home this age?
In order to secure the squeaky boards can I just screw them through to the subfloor? Can I do this anywhere or just at the joists? If just at the joists what is the preferred method of locating the joists? I don't see any nails and the top wooden floor is tounge and groove. How can I go about repairing the hole? It causes a major squeak and the chipped top floor board to depress a little bit when walked over.