Is there any rationale for removing attic floor insulation when converting to an unvented attic with an insulated roof deck?
With or without ducts in the attic, if the mean wintertime attic temps exceed the dew point of conditioned space air by some margin with the roof deck insulation is in place, moisture issues in the attic would be well-controlled, and in summertime even more so, with less access to humid outdoor air to condense on ducts. I’ve yet to hear/read any reasoning or analysis behind the practice (or of specific instances where leaving it in place caused a problem) yet it seems to be almost a standard with spray-foam installers, independent of climate zone or actual installed R-values.
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