Wall Assembly Retrofit
Hello, I am planning to replace the siding on my house. I have done a lot of reading on this site and am wondering what the best path forward is given the existing home construction. My understanding is that my proposed wall assembly is not ideal for new construction but will work in zone 6. The proposed assembly should breath to the exterior better than the existing wall. Looking for suggestions.
Climate zone 6A (Minneapolis)
House built in 1982
Planning to replace windows and siding
Current Wall Assembly
Fiberboard siding > 1 inch foil faced insulation board > 2×4 wall with unfaced fiberglass insulation > poly vapor barrier > ½” gypsum board
Proposed Wall Assembly
Vinyl siding > WRB > 1.5 or 2in XPS insulation > 2×4 wall with unfaced fiberglass insulation > poly vapor barrier > ½” gypsum board
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In all of your wall descriptions, I don't see any structural sheathing mentioned. Is the wall braced with diagonal let-in bracing or something similar? I ask because we are most concerned about condensation on water-sensitive structural sheathing (generally wood-based sheathings). Without a layer of water-sensitive sheathing, the concern about condensation becomes more about large-volume bulk condensation, as in, enough condensation to pool at the bottom of the wall cavities and/or run out onto the floors or other water-sensitive materials.
That said, your proposed wall will work with or without structural sheathing. With the 2" XPS, the wall approaches the current IRC required R10 exterior and R13 cavity insulation for your climate zone. You could get similar performance from 2.5" EPS foam or 2" GPS foam. Without film facers, these will have higher permeability than XPS, and they are gentler on the environment than XPS, though new XPS formulations are better than the older ones. You may also be able to find recycled EPS or XPS on Craig's list locally for substantially less than new material.
Yes, the walls have diagonal metal bracing on the exterior of the 2x4. Thank you for the information and options.