Plate Height above Sub-floor

OK, I may be calling the two-by at the bottom of a stick built wall section the "plate" in error. It may have another name and I'll be happy to learn it as well if that is the case.
But, for now, I have a question as I re-build the awkward work of a previous owner with whom we can not converse (or trust were we able!).
Tis fellow had "opened up" the kitchen/dining area by simply removing nine or ten studs and the "plate" they had been attached to. As the flooring was either added to (there is a layer of three quarter inch (5-ply) plywood on top of a sub-floor of one-half inch (4-ply) plywood.) or originally built in two steps. The is, the 4-ply is laid over teh floor joists but is under the plates for the walls and the 5- ply lays over that - butted up to the plates in question.
MY CONCERN is that there is insufficient nailing area with half of the plate covered ny the 5-ply. I was intending to added pieces of two-by along the plate I uncovered/replaced (I am replacing the wall section DUFUS removed as it supports the - you guessed it - roof!) which would provide a hefty back stp for any molding to be added later on.
Then again, is this necessary? Is the three quarters of an inch standard some how? For some reason, I thought the plates were nailed to the flooring - but half-inch flooring seems terribly weak and adding the 5-ply after teh walls were up abut before the house was finished (as opposed to a retrofit) seemed extraordinary.
If you "know" this two-layer approach is or is not "standard" I would appreciate the references.
The DUFUS also "opened up the Kitchen" by removing the beams that tie the two walls of the home together and nailing pretty wood (flooring) to the underside of the roof rafters - OH, Boy do I have work to do to fix that "improvement" before the walls tilt out! But that's a "whole 'nuther story/"
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It sounds to me like a 1/2 assed contractor had his framing inspection and the inspector made him add 3/4" subfloor to the 1/2" stuff because it was not up to code. We ~have~ to use 3/4" in NY state. You can add 1/4" ply then 3/4" to bring it up to grade and continue on. Could be your home is a modular and 1/2" was all that was needed and the homeowner didn't like the floor "bounce" and upgraded accordingly. Without looking up into the framing above the kitchen where the 2 walls will tilt out, I would say you need an LVL beam and then box it out by whatever means you want. Drywall. Fake beam (pine) or whatever.
RP
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No, you have it right.

How subflooring is handled is dependent on the type of finish flooring, code and degree of (in)competence. You didn't mention what the joist spacing is, so it's a bit unclear whether the 1/2" was an uninformed decision or a laughable one. I would suggest it doesn't matter.
On the flip side, their intention all along could have been to put the 3/4" on top for some seemed-like-the-best-way-at-the-time reason.
The 3/4" above the floor is acceptable for backing the wall covering and whatever trim you decide on. The studs offer plenty of backing support on their own, so unless you have some unusual high-abuse area, or are using unusual molding, starting and stopping in unusual places, you're probably good to go.

You say before the walls tilt out - how long ago did the collar ties (or ceiling joists/beams) come out? You could, of course, replace what was removed, or you could use cables or rods with turnbuckles attached between opposing rafters. It keeps that open look, if that's what you prefer.
R
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Thank you all for the informed advice and comments. And, in particular for the collar ties replacement idea (wire/rods w/turnbuckles) I'd not thought of.
BTW, the walls are not Yjat anyone has noticed) buckling or tilting. Nut I fear they might.
FYI: The Dufus Remodeling took place about five years ago.
Thanks again.
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