Fireplace masonry chimney penetrations are a major source of air leakage into attics. It is important to use only fire-proof and noncombustible sealing and insulating materials within 3" of the chimney. Fire-resistant silicone sealant is required where high temperatures are present.

The following air sealing procedures are for masonry chimneys that extend through the ceiling into the attic space. The procedure shows the installation of a fire-resistant gypsum board guard or a guard made out of noncombustible insulation board around a masonry chimney to keep combustible insulation at a safe distance from the chimney.