Exterior foam on block walls

hello, i have an uninsulated block wall building with no insulation. plan is 2×4 stud walls inside with rockwool r15, strapped foam exterior with wood siding, i have done this in the past on wood framed buildings and always matched exterior to interior r values as i am in the cold upper north east. do i have to do this with block wall too or can i use less on exterior, was planning on only r-6 exterior? thanks
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Replies
It is the same rules as a regular wall. You can use less exterior rigid if you have a warm side vapor retarder (ie faced batts or smart membrane).
With reduced value exterior rigid, best to select one of the more permeable foam boards. Unfaced EPX/XPS or micro perforated GPS are good options.
thanks, interior will be caulked and well sealed bays, filled with rockwool, certainteed membrane, air tight drywall with latex paint and i forgot to mention, there is also 1/2 inch layer of eps covering the entire interior wall between stud wall and block wall so wood is not in contact with masonry at all. so it sounds like i should be good to go.