Wall retrofit in Climate Zone 4a (borders 3A)
We are renovating our home in central North Carolina, built in 1991. Our climate is listed as a 4A (20 min south is climate 3A). Lots of crawlspace vapor issues, we will be sealing the crawlspace as most of the current moisture issues are coming up through cracks in the sub-flooring near AC vents (Ducts are located in the crawlspace).
I have read so many articles, bulletins and scenarios – none of which meet our exact scenario, rendering me unsure how to proceed. So I have a series of questions for the resident experts and the wall retrofit is the first one:
*Our home exterior walls were built as shown in the attached image. Namely,
Cladding->1/2″ fiber board->2×4 w/R-13 fiberglass batting->plastic sheating->drywall
*Cladding is mostly Masonite except a few areas that the previous owner made mods/repairs which he used Hardie Board.
*Mild mold was found on the plastic/fiberglass facing area in some areas (below kitchen window / behind sink on south facing wall was the worst) – none on wood.
*The outer sheathing of fiberboard (R-3/in and Perm 37) was attached after rafters were done. Sheathing was not notched around rafters and lots of holes for air (and critters) despite back blocking the sheathing on the inside (found dead lizard in the wall).
*Cladding is generally in good condition with the exception of a few locations, so we don’t want to remove all the cladding to redo sheathing. During the renovation process, we will have access to about 1/2 of the sheathing. We are considering replacing all fiber board we have access to with Zip R-3, notching around rafters and sealing with Zip Liquid Flash and Zip Tape at all joints and at the wall top plate.
*80% of all interior wall drywall is being removed and plastic barrier will be removed with the drywall.
*Per other articles on this site, it appears that any thickness of foam (EPS/XPS) placed on the outside will prevent inner cavity condensation in a 4A climate.
1) Will sealing the crawlspace shift the moisture problems – i.e. make the moisture laden exterior air come from other areas such as the poorly sheathed walls and/or attic?
2) Will using Zip R-3 on 1/2 the house and fiber board on the other 1/2 create a moisture/air flow imbalance resulting in higher concentrations of moisture in the “old”, non-Zip R-3 walls?
3) Based on our wall structure and access, what is the best value method to move the vapor/air barrier toward the outside of the structure (toward the fiber board, and away from the drywall) and eliminate (or significantly reduce) condensation?
Thanks in advance!!!