Insulation, Radiant and Vapor Barriers - Vapor Barrier in Basement

Hello,

I am in the process of finishing my basement and am putting up a vapor barrier on all of my outside structure walls. I am using a 6 mil plastic for it. My question is do I need to do this barrier on the walls that are completely underground??? (Concrete) or just the ones that have part of the wall above ground?? If I have to do all of them can I use the 4 mil for the ones below ground. I live in Virginia and I noticed that all the new homes are putting up a vapor barrier. Thanks

I take it when you said outside walls you have the insulation in them and the poly over it on teh room side?

Yes take and hang a 2 or 4 mil poly on all the cement walls tack it to the sill plate. Build the stud walls a P/T for bottom plate. put it up 1" from the cement wall. Put R13 insulation in them paper to the room ,cover this with a 2 or 4 mil poly. Then drywall or panel it ED;)

great thanks