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Insulating rim joist where joist cavity is used for a cold air return.

e9MP7K74xu | Posted in General Questions on

One of the conclusions of a blower door test was to insulate the rim joist with spray foam. Unfortunately there is a cold air return duct that runs length of one side of the house in the cavity shared with the rim joist.

Is there a way do handle this effectively without adding a new duct? I assume spray foam cannot be added inside this space as is.

Zone 5a

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  1. GBA Editor
    Martin Holladay | | #1

    The best solution is to move the duct.

  2. BobHr | | #2

    Is this a 1 or 2 story home. In a 2 story an exterior wall cavity may also be used. If it is a single story home it is easy to move.

  3. GBA Editor
    Martin Holladay | | #3

    I disagree. Exterior wall cavities should never be used for ductwoork.

  4. davidmeiland | | #4

    Robert is saying the rim joist duct might be feeding an exterior wall stack. He's not saying it's OK.

  5. e9MP7K74xu | | #5

    This is a 2-story 1940s home. The return duct feeds two intakes on the first story and one or two from the second, which I believe are via wall cavities unfortunately. The first floor near the wall is always cold in the winter, mostly I assume because of the cold air return/joist. Thanks for the feedback.

  6. user-659915 | | #6

    In that case you'll need to move both the crawl space duct and those to the second floor. If you're serious about your insulation upgrades it's time to bite the bullet.

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