Rock-wool insulation can be installed wherever you’d install fiberglass or any other type of insulation, including walls, floors, ceilings, attics and crawlspaces. However, it’s particularly well-suited for rooms along the cold north side of the house and for interior rooms in need of sound deadening, such as media rooms or music studios.
Because rock wool is highly fire resistant, it’s ideal—and often code-required—for using as a firestop between floors of a house. (During remodeling or new construction, ask the local building inspector to identify specific areas that require rock wool firestops.)
Rock wool is also easy to work with: The firm batts can be cut with a serrated knife or handsaw to fit snugly into place. If it gets wet, water beads up and rolls off without soaking into the fibers. The rock-wool fibers are compacted so tightly together that there’s no chance of the insulation shifting out of position or slumping down, which would dramatically decrease its insulating value.
Note that rock-wool insulation only comes un-faced, meaning there’s no kraft-paper or foil barrier. Depending on the situation, you may need to install an independent permeable membrane to serve as a vapor barrier.