Roxul vs cellulose for flash-and-fill in basement walkout and above
The rear wall of our planned basement will be a framed (stick built) walkout at grade, the other 3 sides will be CMU/foundation.
For the upstairs we are currently planning flash/fill with 2″ closed-cell plus cellulose in 2×6 walls in Zone 4. We thought a lot about Zip+R and other exulation options but the costs were just too high. Flash/Fill or Flash/Batt are a compromise. Depending on the calculator used, the whole wall R-value including thermal bridging considerations ended up being about R17 with this approach.
So my questions are
– is cellulose (on top of 2″ foam) OK for the at-grade framed walkout wall? (not the foundation walls)
– would 3.5″ R14 Roxul comforbatts be better overall than cellulose? cellulose would seem to seal better against an uneven foamed surface, and also has some moisture slow-drying capacity. Roxul has a slightly higher R/inch.
– what is the final word on cellulose and fires? I can’t find a straight answer. I know the fiberglass and cellulose industries are oppositely biased. see (presumably) non-industry articles below.
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