Double insulated rim joist?
onebassist
| Posted in General Questions on
Is spray foam on the rim joist beneficial/necessary if there is already an inch of xps on the exterior of the sheathing? The plan is to use dense packed cellulose in the walls above and below. The framing is 2×6 and this is a doubled 2×10 rim joist. (Zone 4).
Thanks
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Replies
Mike,
The spray foam would be beneficial. It would reduce the chance of air leakage and improve the R-value at this location. Open-cell spray foam makes more sense than closed-cell spray foam in this case, since the rim joist has little opportunity to dry to the outdoors.
Thanks Martin. If open cell foam isn't available, should I go with the closed cell foam anyway?
The contractor has proposed closed cell spray foam in various areas, and I'm not sure if he uses open cell foam. I suppose the other option might be to dense pack cellulose against the doubled joist. The stud-bays above and below will also be getting dense packed cellulose.
Mike,
Your exterior rigid foam is thick enough to keep your rim joist above the dew point in winter, so dense-packed cellulose would be fine in this location.