I am in the beginning phases of a small addition to our early 1900’s home in zone 4a non-coastal Maryland. With this addition, I am planning to add exterior insulation to the existing structure and new siding. The existing interior walls are a mix of plaster and drywall, 2×4 dimensional studs (balloon frame), no insulation, 1×6 dutch lap siding, tar paper, fiber cement shingle siding. What I am considering is removing and properly disposing of the existing siding shingles, adding blown in cellulose to the stud cavities, installing new exterior sheathing over the original wood dutch lap, a wrb, adding 2” roxul comfortboard 80, ventilated rainscreen, Boral true exterior siding. My questions are:
1. For sheathing options, would I get better or more preferable performance from plywood with taped seams and a wrb, or zip with taped seams?
2. If plywood with taped seams is best, should I consider a higher performance vapor open wrb like Deltavent or Blueskin or is this overkill?
Thanks in advance for your input
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