Reinsulate an exterior bath wall in climate zone 6
I’m working on a shower wall remodel in climate zone 6 of a home built in 1950. When I pulled down the old cracked tile, mortar and plaster walls they were about an inch thick. Underneath those walls was R-5 kraft faced batts on 2×4 studs. The exterior of the house has Tyvek and wood sheathing.
The bathtub is staying put so I’m not able to get behind it other than to slide new batts in place. My plan is to replace the batts with R-15 mineral wool. Then, to bring the walls back to the same thickness, attach 2 layers of 1/2″ drywall, encapsulate it in mud and a couple of coats of primer. Then put an 1/8″ laminate type shower surround over it and seal around the tub and window.
Is this assembly enough of an interior vapor retarder for this climate zone? Is there another approach I should be taking before fully encapsulating everything?
Edit: Images attached. I removed all black kraft paper shown before putting in mineral wool.
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