Blue jeans have a good R value, I have cedar, I removed it, ran 2" of R
7.2" foamboard for R 14.4, plus foamed the cavity for R 32. I put 3/8
Osb then tyvek, only to protect the Osb. But Im zone 5 to - 20f. I dont
know your extremes, zone, but im sure cooling is the issue. 1/4"
foamboard of blue or pink is apx R 1.25, foifaced foamboard apx R 1.8R.
Not very much for all that extra work, then you need Osb. If you want to
foam add more the labor is the same, tyvek alone will help alot without
more insulation. There is R 7 foam blown in but it outgasses, and R5
that does not outgas. 1" of 7.2R per inch foamboard would help alot, but
your windows and trim will be recessed, I put in new windows and doors
while doing this, upped attic insulation and new Hvac, my utility bills
are down 75%