Attic – Exposed Mineral Wool
i am in the middle of insulating my attic and have 3” of closed cell insulation on the underside of the roof sheathing. My plan was to install 3 inches of mineral wool on top of the spray foam and leave it exposed to the attic interior to act as an ignition barrier and add to the r value.
My question is does the exposed mineral wool add to the r value of the assembly if there is no air barrier between the mineral wool and the attic interior?
Or do I need to add drywall or another air impermeable material for the mineral wool to add to the assembly’s r value? If so any inexpensive material suggestions?
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