I run a heavy bead of
I run a heavy bead of construction adhesive at the plate to rim joist line and before nailing on the bottom course of sheathing (or standing up wall). Takes care of lateral and vertical infiltration quickly and cheaply.

No joints or leakage with precast panels? You sure?

Indeed!
Indeed!

I’m doing something similar
I’m doing something similar with foam board and spray foam in the exterior wall and band joist, Howard.

I understand how to keep
I understand how to keep energy efficiency in style, I have doing this for awhile. I know the difference between a sweater and a wind breaker, they go better together.

We see this all the time in
We see this all the time in kitchen and bath remodels. We put back Roxul insulation but not sure we did anything to solve the problem. We do insist upon new exhaust fans with all the bells and whistles with built in timers, humidity sensors and we make sure the exhaust is properly vented.
Why not if you already havn’t done so is to present this problem to the insulation manufactures and see if the can improve upon the seal at the top of the foundation for the wrap.

However, it also illustrates the dangers of having “do it yourselfers” remodel their own homes. I assume you pulled a permit for this job. You could have covered the tub during demo to protect it from damage since it looks like you might still use it. Forty-something years old? That means it was built before 1978. Did you follow the EPA lead paint protocol during demo?

The real question is….. Why didn’t you recruit some help and have the entire job done by the time the wife returned? C’mon, they do it all the time on cable TV. They always do the demo, pick selections, rebuild, and complete the job all in 30 or 60 minutes.

How much space between the studs and brick? I want a good drainage plane there, not impeded or interfacing with nasty old permeable Celotex. My first line of thought in brainstorming with my partner would be: 1. remove the Celotex (just that simple, right?) 2. Fish some kind of drainage mat material back there against the brick (Vaproshield Wrapshield RS? I’d love an integrated WRB…Trouble is, no way to mechanically fasten it, still, better than the Celotex). I want a thermal break outside the studs too! (Since we’re in there anyway). My next thought was 3. Maybe in 1’ or 18” horizontal strips, you could fish ½” foam board back there. But there are the Celotex nails – pull them? Flat bar and knuckle buster, boring and takes forever, may not be possible in some places so never mind that thought. So there will now be a gap between the drainage mat and the studs, let’s fill that with some closed cell gun foam. If it expands a little beyond the left and right face of the studs that’s OK. The trick will be to get the gun foam installed without compressing or getting into the drainage mat, but that just takes some finesse, a few light passes. 4. Now install rigid foam board (thickness depending on the remaining gap and desired final R-Value) to align with the plane of the foam-in-back of the studs, careful not to compress the drainage mat. Cut it short on all sides, maybe ½” or so to leave a 1 part foam gap, then 5. foam those joints. 6. Trim foam as required to install grade 1 fiberglass. Or use thicker, (R-13 min) foam board and call it a day. 7. Blower door test it before fiberglass to make sure you’ve got the assembly all airtight. What to do around the top, bottom and sides? Need to give that all some more thought and aside from the obvious (really picky and time consuming) I may be missing some scientific detail, what could go wrong over time?

This is all just a starting point. And there’s the window detail…
At this point, my partner would say (well, first he would say, “crazy person! you want to do WHAT?” is it really worth all that?) then “that won’t work because…” and we would go back and forth until we agreed on something scientifically/structurally sound and humanly possible. Then I would estimate the time and material it will take to install such a beast, add appropriate markups and present to my client who would fall on the floor, get back up and say…but I thought air-sealing and insulating was a cheap and easy way to save energy? What’s the ROI for that? And I would say “LOL” then “well…moisture…” then I would offer option B which is like you said, rigid foam board and spray foam to seal the cavities, pressure test it then grade 1 fiberglass. And try to never think about that Celotex again…or the backside of the brick…or the backside of the studs…all slimy…but at least I would have that analyzed and priced detail in my library for the next one similar, and my client would have made an educated decision.

Makes me want to gut my bathroom – I’ll bet mine is worse than yours! Thanks for sharing and explaining it all!

If the sheathing is touching the back of the brick and the brick gets any direct exposure to wind driven rain or heavy roof runoff, then it is only a matter of time before the sheathing, the stud and in the inside of the wall will be wet too.

Short of replacing the brick wall, or removing a few bricks sufficient to reattach the sheathing properly, you might consider stuffing the cavity with Mortar Net or similar to assure that the sheathing doesn’t touch the brick, and try to seal the ends of the board to the stud with foil tape and then sealant compatible with the insulation materials.

You might also consider two temporary holes through the Celotex board to allow for some temporary pressure from the inside to pull the board back onto the stud with a heavy wire or hook. After the stud sealant is cured, the wires can be removed or cut and the small holes filled with a bead of sealant.

This is a fussy detail to have to build from the inside, but I can’t wait to see the final resolution. Good Luck.

Cameron, that’s pretty much
Cameron, that’s pretty much my plan, except that I’m going to use spray foam to seal the foam board in place. I’ll spray the edges of the cavity before setting the foam board in there and then set the board into the spray foam before it cures. Then I’ll spray more around the edges on the front side of the foam board. Also, I’m planning to use 1/2″ board instead of 3/4″.

Yeah, our subfloor is rotted out between the tub and toilet, too. Once I get the tub out, I’ve got to replace the two layers of rotten plywood. The toilet and tub were still adequately supported, but if I put all my weight on the rotten plywood, I’d probably go through.