Decision time – GreenBuildingAdvisor

I previously asked about 2×8 walls and a cathedral ceiling in this post https://www.greenbuildingadvisor.com/question/whats-the-good-enough-wall-assembly-under-cedar-shingles

Context is: DC area of Maryland (Climate Zone 4). We are using cedar shingles (WRC) for siding, the shingles will be installed over classic slicker by B. Obodyke, applied over Henry Blueskin VP100 applied to the 1/2″ 5 ply plywood sheathing.

I proceeded with 2×8 walls and 2×10 cathedral rafters. I will have an unvented roof assembly with closed cell spray foam exceeding R-49 (following Martin H’s advice in the 5 cathedral ceilings article and followup questions).

I had planned to use R-30 Rockwool for the stud cavities, floowing Akos’ advice in the Q&A linked above.

I got quotes and all the places have Rockwool around $5-7k more than putting in open cell foam in the walls.

So, in my wall assembly described above, in my climate zone, is there any concern about using open cell foam filling the 7.5″ wall cavity vs. using R-30 of mineral wool?

Thanks everyone.