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Community and Q&A

Insulating rim joists between first and second floor

mason13a | Posted in Energy Efficiency and Durability on

We’re putting a second floor on our home. The builder used composite wood i-beams between the first and second floors. The builder said they don’t plan to insulate the ends of the i-beams (rim joists?) along the edges of the house. There’s no other insulation between the first and second floors, in between the i-beams. I found this article that talks about using spray foam to insulate rim joists:

Insulating the outer envelope between floors makes sense to me, but the builder doesn’t see it as necessary. Are there different views on whether this insulation is needed?

Thank you in advance for your comments/thoughts,

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  1. Expert Member

    Where are you located? I don't know of any building codes that allow for uninsulated rims. As Dana said though, the more important task is air-sealing this junction between the walls and the floor.

  2. Chaubenee | | #2

    Put foam outside your sheathing and under your siding. It is a no-brainer.

  3. Dana1 | | #3

    The builder is truly clueless about heat transfer. Even with rose colored glasses it should be pretty easy to spot the uninsulated band joist in this picture:

    Of COURSE the band joists need to be insulated, at least to the same level of the walls. They need to be air sealed as well.

  4. mason13a | | #4

    Thank you, D Dorsett, Malcolm, and Joe, for all your responses and helpful information. I am in Maryland.

  5. GBA Editor
    Martin Holladay | | #5

    You've gotten good answers to your question. Of course your rim joists need to be insulated.

    Here is a link to another article with information on the topic: Insulating rim joists.

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