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Water/air/thermal seal for chimney joint

woobagoobaa | Posted in General Questions on

We are proceeding to Blueskin our old board sheathing and are about to tackle the joint to the exterior chimney.  Please see interior pic attached.  How best to water / air seal this gap?  Note the heat pipe to the right .. no idea how that avoided a freeze in Zone 5. 

Also, the wall assembly inboard of the chimney is 2×4 with no way to extend the cavity.  Is mineral wool my only thermal insulation option for direct contact with the chimney?


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  1. user-2310254 | | #1


    See this article ( for best practices such as:

    "Gaps around brick chimneys are dealt with differently than holes above soffits. Because chimneys can be hot, these gaps should be covered with sheet metal, not rigid foam. After nailing four pieces of sheet metal in place — one on each side of the chimney — the seams where the metal pieces overlap and the gaps between the metal and the chimney can be sealed with high-temperature silicone caulk."

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