On 30 Sep 2006 05:42:20 -0700, "marson" wrote:

the moisture barrier under a slab does not function the same as a
moisture barrier on a wall. the under slab barrier's role is to block
moisture movement by capillary action from the ground into the
concrete. a vapor barrier on a wall is blocking moisture from moving
from inside the heated space into the insulated wall cavity.

I talked with a plumber about that a couple of months ago (making
converation at a job site) and his contention was that the vapor
barrier was to help prevent Radon emissions and had little to do with
moisture, but as another poster pointed out, opinions are like
assholes.

i believe the IRC was recently changed to allow NO vapor barrier if
foam is used under the slab (since the foam blocks capillary action
anyway).

Depends on the county inspector- some places, they don't care and
won't enforce it, other places they do. But as I understand it, it's
still in the code.