Mineral wool over open-cell spray foam
I’m finishing up a 1980sqft single story house. I have 5.5″ of OS spray foam on the roof deck (conditioned attic) that needs to be covered for fire code reasons.
My options are:
Drywall under $500
Sprayed on thermal barrier $2120
R15 mineral wool $2000
I’m leaning to the mineral wool over spray foam. Is this a smart/safe assembly?
Will water vapor be a problem in the small gap between the foam and the mineral wool
I’m in zone 4A central NC