Redoing siding and rethinking indoor swimming pool wall insulation. Need advice on moisture management and choice of insulation. – GreenBuildingAdvisor

I am planning to replace siding on the entire house, and while I am clear on the route I want to take with adding a layer of continuous Roxul on the main side of the house (built in 60s, already replaced fiberglass with Roxul batts when I redid drywall), we have an indoor pool in an attached building that was built in ’93. I am controlling RH rather well, since we have an automatic pool cover that is closed anytime the pool is not used, and I have a dehumidifier that only runs when the pool is open. The size of the pool is 20X40, so a lot of evaporation when open, and the RH goes up to about 70% during that hour or so we use it each day, but then in the next couple of hours, the dehumidifier knocks it down back into the 50s.

The current wall cross-section detail is attached.

I am considering removing the siding and 1/2 CDX sheathing and replacing the fiberglass with a flash layer of closed-cell and Roxul for the rest of the cavity. Then, I would wrap the Zip-R sheathing and siding with a rainscreen behind it.

Why do that? My concern is that moisture was not managed well before, like in the rest of the house, so when I open that wall, I may find what I found in the rest of the house – crumbled vapor barrier (plastic) and fiberglass batts gray from dust and mold. Would be nice to have tighter air infiltration control so I need to heat the building less in the winter.

I am not very good at understanding vapor drive with natatoriums, so that is one area I would like to get educated on.

Any advice, direction, or places to look for info would be appreciated.

I am in Boston MA.