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basement rim joist sealing xps and caulk or spf?

Posted by dgeist (My Page) on
Wed, Dec 11, 13 at 10:46

I'm planning on sealing/insulating my rim joists with a combination of extruded foam boards and one-part SPF (likely great-stuff fireblock or similar). My questions are two-fold:
- I plan on making fairly snug XPS blocks and sealing the perimeter of each block with either caulking or a foam bead. Foam is obviously a bit quicker. Has anyone had issues with this system and had to use caulking due to seasonal expansion/contraction (I'm in a moderate climate)?
- I'd love to use polyiso for its fire-rating, but can't source the 2" anywhere near me. Can I use a skim (1/2") of polyiso on top of the XPS and get similar fire resistance or does a fire-rated spray covering make more sense. The basement is partially finished, hence the desire for fire rating.

Dan


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RE: basement rim joist sealing xps and caulk or spf?

According to the Polyisocynanurate Insulation Manufacturer's Association, "polyiso...is generally required to have a thermal barrier. But, it has the capability to be used without a thermal barrier when proven by test. ...Consult a specific polyiso manufacturer for code approval data allowing a product’s use without a thermal barrier."

And the question is whether 1/2" of the polyiso you choose meets the testing requirements of ASTM E84.


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