Insulation dilemma: Mineral wool batts, encapsulated fiberglass, and rigid boards
The Insulation Situation:
(Mixed Humid region) Asheville NC
Older 1968 800 sq ft house; prior owner had roof leak. Shingles replaced 1 yr ago, no more roof leak. Currently doing mold remediation on framing.Gutted all ceiling & most of sheetrock walls. All old fiberglass insul removed in attic & most walls due to mold on dust, some blackboard sheathing removed due to mold growth. House has aluminum siding exterior.
Approach: I only have access from interior to replace Insulation. I will first do thorough air sealing. Due to removal of old/damaged blackboard sheathing removefrom 2×4 studs, i now have thermal bridging to address on one side of the home.
I would like to use a rigid board (whether Xps Foam or Rockwool ComfortBoard 80) directly onto the Ceiling joists and the wall joists (whereby, i then would have non-paperbacked sheetrock eventually installed by a contractor). I want to install the insulation board across the studs, in order to address thermal bridging from the INSIDE walls and/or to give extra insulative value that i cannot obtain simply with one layer of the cavity insulation ( in attic for example) whether Poly encap FG, or Rock wool).
And into the interior cavities, before i install the board and sheetrock, i am trying to decide between Poly encapsulated Fiberglass an/or Rockwool batts. Obviously, these both have very different permeance/permeability.
No matter how much i study, research, and ask people, i am getting mixed messages as to what is safe, considering the mixed humid climate here… is the XPS rigid board ( is it a Category III?) unwise to use on the interior rafters due to its less permeable features, compared to say, Rockwool Board? Which is the better to prevent moisture problems in my area? Yes, we will be installing a heat pump, so the house will have AC as well.
Please advise as to the best approach with the options i am considering as outlined in the discussion above, why one combination would or would not work over the other. Problems i might have with a particular material or assembly. Apparently, in my Mixed humid region,( area 4) i DONT need a vapor barrier beyond a simple category 3… so would using the XPS rigid board om inside of house create a problem? I am needing to do the insulation install DIY, due to other pricey hvac we do have to hire out… one of the main reasons why i am considering these materials.
Practical & time tested advice on these specific issues at hand would be appreciated.
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