Getting a good air seal around chimneys – be it masonry or metal – is always challenging. Although the details could be more clearly defined, I was happy to stumble on Natural Resources Canada’s following detailed drawings in the latest version of Keeping The Heat In:
Though in concept good, there are two clarifications the illustrator needs to more clearly define. It would be nice to know if the ceiling flange (labeled ‘fire stop’) connects to the outside face of the chimney or the outside face of the radiation barrier. Also, the detail showing the detail showing the air and vapour barrier needs to be clarified, it just shows up.
Here too the illustrator should show a bead of acoustical sealant on the cut away for clarity. This detail relies on dimensional lumber to carry the air seal, so where cross-cut, sealant or tape needs to be applied.