Hello GBA community,

Every time you come up on the FHB podcast (quite frequently), I think to myself, “man, I really need to get around to asking that question.” Thanks for taking the time to read my question, and for all the great content you put out.

My wife and I are conducting a gut-and-remodel on a house from the 60s. We’re in mid-Missouri, climate zone 4. The wall assembly was originally [brick, air gap, poly? sheeting, 5/8″ fiberboard, 2×4 studs with kraft-faced fiberglass, drywall+plaster]. We’re down to the inside studs, and I’d like to fill the cavity with Rockwool (R15).

On top of the studs, I’m considering using 1″ foil-faced polyiso foam with taped seams. This would get the assembly up to R21, reduce thermal bridging, and provide a good air barrier. However, I’m worried about trapping moisture within the wall assembly (since I’m not sure what that exterior plastic wrap is/is doing). My brow is especially furrowed as I try to unravel whether Missouri wants to be a warming or a cooling climate. We have hot, humid summers and frigid winters. (ChatGPT recommended that I physically switch which side of the wall my vapor barrier is on every season).

My questions are: Am I worrying over nothing? Am I about to make a huge, fatal mistake that will rot out my walls in 5 years? Should I be grateful for my barely-above-code R15 wall? Do you have any other recommendations for a safer assembly? 

Thanks again for reading my question,
Caleb