Procedure: Masonry Chimney with Gypsum Board Guard
Expose the ceiling finish board approximately 12" on all sides of the chimney.Install silicone sealant around joists and blocking to seal the ceiling finish to the framing. Install silicone sealant along the top side of the joists and blocking in order to adhere and seal the sheet metal closure.Cut and install the sheet metal closure to fit over the chimney opening tight to the masonry chimney, with overlap at each joint.Seal the metal closure to the chimney and at each joint with silicone sealant. Sealant should be applied between the metal closures prior to installation of the second closure piece to ensure continuity of the air barrier.Install a framed gypsum board insulation guard around joist framing. Allow 3" space between the insulation guard and the masonry chimney. Size it so that the top edge is above the insulation, including any additional insulation that may be added. Replace existing insulation and install additional insulation around chimney insulation guard.As an alternative to step 5, install 3" thick of noncombustible insulation boards around the chimney to at least the height of the additional insulation. Replace existing insulation and install additional insulation around the insulation boards.
