Hi there – Looking to reinsulate a bedroom. We are in Rochester NY climate zone 5. The room has two exterior walls, one northern facing and the other eastern. The wall assembly is vinyl siding, ¼ inch foam backer board, tar paper, plywood/osb, 2×4 16 oc studs w/ R11 faced insulation, rock-lathe/plaster walls. 1970s home.

I want to reinsulate the room but prefer not to demo the plaster walls. Seeking advice on adding rigid foam on top of the plaster walls (using adhesive and/or nails) and then cover with ½ inch drywall. I’ve read on these forums and others that this would work in my situation. Alternatively I could also use 1×3 or plywood strips to fur out between rigid foam and new drywall to help with screws popping.

Ideally I would approach this from the exterior but its not currently feasible. Any comments or concerns with this assembly? Any thoughts on drywall straight on rigid foam vs on 1×3 strips. Lastly I was thinking of using 2 inch XPS since I have left over from a basement project. Would that cause any issues? Planning on taping seams and using 3-4 inch screws. 

Thanks in advance!