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Community and Q&A

Air-Sealing and Thermal Bridging of Fire Walls

agm413 | Posted in Green Building Techniques on


(climate zone 4)

For a set of 6-7 connected townhouses, is one of the middle units able to be a warm roof with exterior insulation while the surrounding are cold roofs?

My main concern with this is the air sealing + thermal bridging of  the fire walls between units which seems to just be an uninsulated CMU type wall for soundproofing + fire wall code. Would one need to spray foam or use rigid insulation to break that thermal bridge and air seal?



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  1. Expert Member
    BILL WICHERS | | #1

    You probably wouldn't be able to do this with rigid foam, since that would go on the exterior of the sheathing and would make it difficult to keep the roofline consistent. You'd probably need to go with spray foam n the one hot roof unit, since that would be applied to the underside of the sheathing.

    I'm not sure exactly how you'd have to do the fire sealing. On commercial buildings, the "seal" us usually a combination of mineral wool and intumescent fire sealants or putty products. This won't have a nice finished appearance though, so you'd need to box over it if this was going to be inside of finished living space. I would run your proposed solution past your inspectors prior to installing anything here.

    Note that you might just want to tolerate a bit of thermal briding at the paritions between units since the fire blocking part of those walls is more important than the thermal insulation part. Life safety prevails over energy saving stuff in terms of codes.


    1. agm413 | | #2

      Thanks for the feedback. For the roof there are some separators that are like a triangle between each unit , probably to facilitate water draining. But that was also another worry is how it'd work with those/other roofs.

      I was hoping to not have to do it on the interior side since you'd pretty much have to remove the ceiling. The "attic" is 2x4 joists, about 18 inches of space, then 2x8 (maybe 2x10 I forget) rafters, so no easy way to remove the current insulation then spray without removing the ceiling drywall.

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