nailbags, I'm guessing you are in zone 4c, which is required to have a class 1 or 2 vapor barrier. (according to the link provided by Gary above)
Also from that link...
"No interior vapor control required on the interior side of framed walls in climate zones 1, 2, 3, 4a, or 4b. In hot, humid climates, a Class I or II vapor control layer on the interior of the framing can, and often does, cause premature building enclosure failure due to inward moisture drive condensation (see RR-9302: Humidity Control in the Humid South
). BSC recommends avoiding Class I or II vapor control layer on the interior in these zones, or any material that acts inadvertently like a Class I or II vapor control layer such as reflective foil insulations, vinyl wall coverings, glass mirrors and epoxy paints."
If that is indeed true, then why the heck do people tout the use of 2" XPS in rim joists (see other thread) which I believe is a class 2 vapor barrier?