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How do I air-seal the crack around a chimney?

Jack Woolfe | Posted in General Questions on

What are the best ways to seal either a Metalbestos-type or a masonry chimney as it penetrates the air/vapor barrier in a ceiling?

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  1. GBA Editor
    Martin Holladay | | #1

    Check with the manufacturer of the metal chimney; install the necessary transition pieces and follow the manufacturer's recommendations for air sealing.

    The crack around a masonry chimney should be sealed with metal flashing. The seams and edges of the metal flashing should be sealed with high-temperature silicone caulk.

  2. GBA Editor
    Martin Holladay | | #2

    Here's a Fine Homebuilding tip from Charles Miller addressing your question. I think he should have installed caulk between the ceiling joist and the metal flashing, and he should have mentioned the need for high-temperature caulk at the flashing seams, but otherwise his advice is good:
    Sealing an air leak next to a chimney

  3. Jack Woolfe | | #3

    Thanks, Martin. Just the information I was looking for :)

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