The Space around the Chimney Needs a Fire-Resistant Seal

here’s usually a 2-in.-wide gap, required by code, between framing and masonry chimneys. To close the gap, I first stuff it with rockwool (1), then apply a bead of adhesive caulk to the framing (2). Next, I screw down wide strips of metal (recycled drip edge)
along the perimeter (3). I seal the metal to the chim­ney with fire-rated intumescent caulk (4). For continu­ity, you need to seal the ceiling joists to the drywall below and at inside/outside corners of the rough opening with expanding foam.