Rim joists (vapor barrier?)


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Old 09-20-22, 12:26 PM
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Rim joists (vapor barrier?)

Had condensation and insect issues in the basement with our home. Turned out that the builder just put pink insulation into the rim joists and there were a ton of gaps in the sill as well. So, I filled the sill gaps with can foam and put 1.5" XPS foamular into the joists and sealed those with can foam. Then R22 went over that.

However, many spots were tight due to plumbing and HVAC and I was only able to fit 1" XPS in those and less R22..

My question is, do I need vapor barrier over any or all of this?

Note: the basement walls are just R22 with vapor barrier to the joists (No foam board).

 
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Old 09-20-22, 04:21 PM
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The foam is sufficient as a vapor barrier as long as you air seal the edges. If air blows past it, it's not doing much as a barrier at all. Problem is, you can get condensation on the interior surface of that foam (only on the coldest of days) if it's not thick enough. 2" is best, but you do what you can.
 
 

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