I have a condo with an entry hallway which slopes. (It's in Back Back Boston. Everything there slopes.) I want to correct it by taking up the current hardwood flooring, sistering level joists to the sloping ones, and putting *the same hardwood* back down.

Based on two other rooms, I am sure there is no subfloor beneath the hardwood, it is nailed directly to the joists. Certainly surprised me when I saw it with my own eyes. (Building rehabbed in 1956.) I cannot add subfloor because of floor height and metal entryway door which cannot be trimmed, so I am limited to the thickness of the hardwood.

I am told by several that it will be "impossible" to bring up the hardwood without major damage, owing to the kind of fasteners they used then, the length of time they've been in place, etc. etc. I am figuring on 25% breakage (there is an adjacent closet where I can get replacement, then put "new" in the closet where it won't show so much.)

Opinions, which I understand are guesses, as to the likelihood of bringing up hardwood of this vintage? (It's oak, narrow plank. Refinished once, by a professional, about 5 years ago.) I am very handy, not a pro, but have done several major remodels including bathrooms, porches, etc. down to the studs and back out again. I would like to preserve the "original" as much as possible, since it is the same throughout the unit, and having just one hallway "new" would look, well, like a patch job. (I accept that in a closet, not in the entry hallway.)

You really don't know for sure, until you get into it. I would start in the closet if possible, and experiment with different tools and techniques.

If you take the door jamb casings and base trim off you will only have to damage the first board removed, unless you have a transition to get in and under with. A plunge cut saw will be your friend.

Under walls, and adding "dead wood", if the walls are in fact built on top of the flooring.