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"2108 IRC 806.2 requires attic ventilation at a rate of 1/150 as a base.  Exc. #1 allows a reduction in rate to 1/300 if in CZ 6,7,or 8 with a class I or II vapor retarder.  I have chewed on this for a while and can't definitively decide on whether this means the exception only applies to CZ 6,7 or 8, and if in a CZ 5 then there is no exception, OR if exc. #1 means that if you are in CZ 5 then you don't need the VR to satisfy that exception.\n\nNutshell: Given a ventilated attic, in CZ 5, with a 50/50 split to satisfy exc. #2, is the required rate 1/150 or 1/300?"
<https://www.thebuildingcodeforum.com/forum/threads/irc-806-2-exception.36742/>