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Air sealing and insulating up to a chimney?

tina81 | Posted in General Questions on

Hi guys!

I’m looking for some advice on insulating and air sealing near a fireplace and chimney in my house (zone 6a). The chimney is unlined and the furnace and water heater are vented up chimney. I’m not going to use the fireplace as is, but I’m planning to put in a wood burning stove insert at a later time. Looking at the attached pictures, do you have ideas on how to air seal the space between the right of the chimney and the framing. Can I fill this space with mineral wool insulation? For the rest of the house I used mineral wool with membrain. Thanks, I appreciate any help!

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  1. Expert Member
    Dana Dorsett | | #1

    Code requires you leave the space empty of insulation, but you can use sheet metal air barriers with fire-rated caulk between floors, and to close off the space. The MemBrain has to stop at the last stud, can't be in contact with the masonry. Read the clearance details of the IRC carefully:

  2. GBA Editor
    Martin Holladay | | #2

    The method described by Dana is discussed in this article: Air Sealing an Attic.

    Although the article talks about penetrations through an attic floor, the same method can be used to air seal the vertical gaps in your photos.

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