Tearing out hardwood floor and subfloor; what about under plaster walls?

House was built in 1929, plaster walls throughout.
I have been unable to convince my beautiful lady (she may wind up seeing this) to let me try to refinish the existing hardwood floor under the carpet we tore up (living room, first floor, with basement underneath). In addition, a friend whose opinion I trust said I should go ahead and replace the diagonal tongue-in-groove subfloor as well (it creaks like absolute crazy along every inch, even when the 20-lb dog walks around; every step is squeak-squeak-groan-creak). I was hesitant to do this, because I'm all about trying to keep as much original stuff as possible (I'm one of those grizzled old-timers that believes, whether I have proof for it or not, that they just did things better "back in the day"), but I can see his point about possibly needing to level the floor out better, plus, with the amount of creaking we've got, and with the floor visibly bowing under one's feet when we walk around, the number of screws we'd have to re-tighten, shims to put in under the original subfloor, etc., it would just be better to rip it all up and put in plywood subfloor. The joists don't seem to be the problem, but even if they are, I'd rather fix it at its source (adding joist shims before doing the floor) than keep ramming the little shim here and there in 500 places.
AAAAANYWAY, my question is this: these are plaster walls, and the subfloor goes farther underneath the wall than I will be able to get to to remove the subfloor in the room completely. I can use a whipsaw and remove it up to flush with the inside surface of the wall, but there's still going to be little pieces/strips of subfloor under the wall where I can't get to to remove it. Is that bad? Would a lot of you call that a botch job, to remove as much subfloor as we can possibly get to, but leaving that little amount under the actual wall? The guy advising me says there's really nothing else to do; the original builders (or at least, whoever did this room as it is now) did the floor, then they did the walls on top of it, so I can't get access under wall to remove the small amount of subfloor under the plaster wall.
So we're going to put in little spacers in between the joists up to the edge of the wall, just to have surfaces to nail the edge of the subfloor into, but there's still going to be little strips of subfloor under the actual wall.
Again; is this normal, or would it be considered cuttng corners/botching the job/leaving heartache for future work?
Any advice, opinions, etc. would be appreciated, and thanks for reading.
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Red Flag! BOWING when you walk around? Bowing as in warped hardwood riding above the subloor, or bowing as in the entire floor bouncing or flexing when you walk, joists and all? What size joists, what spacing, and what span? What is holding up the ends? I'm not expert enough to run the numbers in my head, but others on here are. Even if the size and span are within modern specs, if it was never cross-braced properly, that may explain a whole lot of the squeaking. The time for expert advice is before you rip everything apart, so the engineer or architect (or even a well-experienced carpernter) can see the 'as found' condition. The floor system may well need more than shims- once you have it opened up, you may well need some or all of the joists sistered (which is an easy way to level the topside) and/or a helper crossbeam added in the basement. Nothing wrong with diagonal 1x as the subfloor if it is in good condition and well fastened, but if the topside is uneven, a modern subfloor will definitely make the new floor easier to lay. If it is only a little uneven, a common fix is a thin plywood overlay, but if you strip back to the joists, construction adhesive and screws will make a very stiff floor for you. As to your posted question about how to transition to the old subfloor buried under the walls- yeah, just add blocking or a sistered piece of 2x6 or something to give a good nailer and catch the weight. As long as the joint is buried up under the baseboard you will be fine. The doorways will be harder than the walls, especially if the floor in adjoining room is out of level. A feathered threshold strip, whittled to fit, is a common solution. The subfloor, in the last 90-100 years, pretty much always goes under the walls- you lay the joists, deck them over, then build and tilt up the walls over. Some styles of balloon framing would be the only exception I can think of.
With the kind of money you will be sinking into this, even if you do some or all of the work yourself, a few hundred for a professional site survey, would be real cheap insurance. IMHO, of course.
aem sends....
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needed along the walls. Caulking, the new flooring, baseboards, and shoe mold (if used) will cover any gaps. There is no practical way (or need) to replace wood under a wall without removing the wall.
Don Young
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There is nothing wrong with a diagonal tongue in groove subfloor. Before ripping it out make sure that the subfloor is your problem.

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