Vapor Retarder Between Ceiling and Vented Attic
This may sound like a dumb question, but I want to make sure I get it right. I have not seen much discussion about a vapor barrier between the ceiling and a vented attic. So:
1) Clearly understand the need for an air barrier, but I just want to confirm that in a typical vented attic with something like blown cellulose that a vapor barrier is not needed.
2) Separately, in the case of a ceiling service cavity, would that change the requirement for a vapor barrier? Per the codes requiring a vapor barrier for an un-vented space, would this apply? Does a lack of air sealing on the interior side of the service cavity make it vented?
3) In the summer, why doesn’t condensation in a vented attic become a problem? If you have unlimited moisture from outside at a high temp/humidity and air permeable insulation like loose cellulose, combined with AC cooling the interior, wouldn’t it be common to have a spot in the insulation or exterior surface of the ceiling that is at the dew point?
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