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Community and Q&A

How to Create Thermal Break at Rim Joists with Bonfiglioli Walls

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We’re building a home in central Maine (climate zone 6) and are planning to use Bonfiglioli inspired walls ( to cut down on the cost of exterior insulation. We’re building a two-story on a slab and I’m trying to figure out how to thermally break our joists at the second-floor rim joist. I’ve been considering bumping the rim joist in 1-2 inches and putting 1-2 inches of rigid insulation between the rim joist and the sheathing (7/16″ ZIP). I ran this past a builder friend who was concerned about potential moisture build-up between the foam and the rim joist where we wouldn’t notice it until a major structural component of the home failed. A few questions:

-If we used spray foam on the interior side of the rim joist, would the air barrier that creates eliminate the risk of using rigid insulation between the rim joist and the sheathing?

-If we used 2 inches of rigid rock wool between the rim joist and the sheathing, would moisture build-up still be a concern?

Without a thermal break at the rim joists, the walls would still have a total u-factor that would be below the code requirement, so if necessary, we can just insulate the rim joist on the interior side and call it a day.

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  1. user-2310254 | | #1

    Whatever you do you still need to pay attention to creating a well-detailed water and air barrier on the exterior. And you need to monitor and manage interior humidity levels. That’s how you’ll minimize risk to the structure over the long term.

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