 Sealing around chimneys can be tricky, because fire safety requires that you leave at least two inches between the chimney and any combustible material, such as wood. Unless sealed, that gap would be a massive air leak.
For masonry chimneys, light weight aluminum flashing is easy to find and use. Place the flashing next to the ceiling, if possible. During chimney construction the mason can lay the flashing into a course, much like counter flashing on a roof. Or you could leave the sealing for another worker. In this case, bend the flashing into an L-shape. Run a generous bead of fire-rated sealant along the chimney. Press one leg of the flashing into this bed of sealant. Secure the flashing with at least two masonry nails. Attach the other leg of the flashing to the ceiling framing.
Metal woodstove flues can be even easier, because they almost always have a trim ring that covers the hole in the ceiling. Apply fire-rated caulk where the flue meets the trim piece. Run another bead between the trim and ceiling drywall. These joints will move over time and the seals will eventually break, so someone will have to re-caulk. Luckily, the joints are accessible. |
