WRB for painted T1-11 plywood sheathing prior to new siding?
We live in Climate Zone 5 in Southeast Michigan and want to add 3 inches of exterior Rockwool insulation, 1×3 furring, then new fiber cement siding over existing, painted plywood T1-11 siding. We believe the T1-11 was installed in 1989, when the house was significantly expanded from the original 1932 lake cottage. In the old section of the house, the ¾” T1-11 is installed over original ¾” horizontal T&G wood siding, and there is 1/2” foil-faced board insulation between the studs and the T&G siding. In the “new” section of the house, there is only ¾” T1-11 and does not appear to be a WRB. My question is, what do I use as a WRB on top of the T1-11, prior to rockwool, rain screen and new siding, since the T1-11 has at least 3 coats of paint on it and acts as a vapor retarder? Do I skip the WRB and just try to seal the joints and seams of the T1-11 as best as possible? Or do I add a vapor permeable WRB? The house is not very air tight currently but this siding upgrade will be the start of a lot of effort to tighten it up as much as possible (including new fiberglass windows, attic insulation and sealing, etc…). Thanks in advance for the advice.
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