The purpose of the metal tie specified in R602.6.1 is to ensure lateral distribution of the vertical load born by the top plate. Non-bearing walls have no vertical load on the top plate and therefore no metal tie is required in this chapter. You would still need to meet the requirements to protect piping, wiring, or equipment (.e.g, M1308.2 and P2603.2.1).
I haven't found a good discussion of a centered hole in a top plate. I would argue that IRC Chapter 6 requires only one metal tie under any circumstance and if the hole is centered then it doesn't matter which side you install it on. But again, if we are talking 2x4 framing then pipe/wire protection may drive a requirement for metal ties on both sides of an interior wall.
Regarding double top-plates see IRC Interpretation No. 15-03
Q1: Where a wood stud wall is capped with a double top plate, is the
1.5-inch metal tie as described required on both of the top plates?
A1: No. Where a double top plate is used, a single 1.5-inch metal tie
is required on the uppermost plate only. No tie is required at the
notched lower plate. This is illustrated in Figure R602.3(2) and
Figure R602.3.1.
Simpson has a good reference for Intallation of Utilities in Wood Frame Construction. Combines structural and nail protection requirements for residential and commercial codes. If you are framing with 2x4's it is likely that the pipe protection requirements will push you to use PSPN516 (load bearing) or PSPN58 (non-load bearing) rather than one of the RPS repair straps.
We worry about verticals loading AND horizontal loading. Resting the joists on the double top plate works great for vertical loading and using hangers to keep them aligned until the loft floor sheathing is installed is a great idea, because you can’t end nail them through the rim joist. (A cheaper clip, like Simpson’s A34 or A35 on one side of each joist would work too.)
However, I’d worry about 1) spacing of the joists, 2) securing that overhead load to the vertical supports (stud wall), 3) keeping the loft from rotating or moving away from the main building.
1) You said, “above you office”, so it’s not residential storage. The Code requires a minimum of 125 lbs. per square foot for light loads and 250 lbs. per square foot for heavy loads. (See ICC Table 1607.1.) That means those 2x6’s need to be 12” oc to span you 8’ loft.
2) You don’t have to design against wind loading, because you’re inside another building. However, depending where you’re located, seismic loading could be severe and you can’t rely on toe-nailing to secure the loft framing to the studs.
I’d use either a clip from the joist to the top plate or studs at about 24” oc or I’d use plywood sheathing to hold the joists to the top plate (and keep the loft framing rigid...but more about that in item 3) below. )
When you have a lot of weight up in the air, an earthquake can get (and keep) it moving. Gypsum board (wallboard) can resist this movement, but it’s fairly weak. OSB board or plywood is much better. If you told me you were going to store your Christmas decorations up there I’d thing gypsum board would work. But if you are putting books, dead files, or that old transmission you were going to fix someday, up there, I’d worry....then you’re well into the 250 lbs. per square foot.
3) The whole loft needs to be rigid enough to keep everything in the loft off your head while you’re preparing your will. I like 1/2” plywood nailed at 6” oc to all WALLS and all supports, including the loft rim joists. That way you solve item 2) above, and item 3).
Fastening the office and loft to the main building is a good idea, but I’d need more info on type of building, height, material, etc.
Best Answer
As long as the studs were end-nailed (not toenailed), they will be fine for re-use. If you are remotely concerned and time isn't really an issue, cut 3/4" off the ends and put in an extra plate. (The extra plate might help with raising the wall, too.)