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Community and Q&A

Air sealing a masonry party wall?

Aaron Dent | Posted in Energy Efficiency and Durability on

Does anyone have any insulation and/or air sealing details for a shared masonry wall separating two homes. The masonry extends into the attic and was identified as being very leaky in a recent blower door test.

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  1. GBA Editor
    Martin Holladay | | #1

    One of the most important locations to air seal such a wall is where it penetrates the thermal envelope of your home. That means you have to seal the crack between the wall and your ceiling air barrier.

    If you don't have insulation on your side of the wall, it is a huge thermal bridge, and air sealing won't solve all your problems. Such a wall needs to be continuously insulated on the interior side (your side).

  2. Aaron Dent | | #2

    What about insulating on both sides of the wall and the top of the wall in the attic space (if this is possible)? This should work rather than insulating the inside wall on both sides of the party wall. Issue there is that there is the kitchen on the party wall - really expensive to fix.

  3. GBA Editor
    Martin Holladay | | #3

    Most masonry party walls are firebreak walls that penetrate the roof. Where does your masonry wall end? In the attic?

  4. Aaron Dent | | #4

    Yes, the wall terminates somewhere in the attic - it doesn't go past the roofline at all

  5. GBA Editor
    Martin Holladay | | #5

    Then it should be possible to wrap both sides and the top of the masonry wall in the attic. The trick will be to ensure that the attic insulation on your neighbor's side of the wall is continuous with your neighbor's attic insulation. Assuming you can ensure the continuity of the thermal barrier, this approach would work.

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