My husband and I are building new, a split-level home. We are having contractors finish one room and we are finishing the other rooms ourselves. The contractors built a 2x4 wall around the lower portion and put vapor barrier(plastic) BETWEEN THE CONCRETE POURED FOUNDATION AND THE 2X4 WALL. My husband did the same in the family room as he was copying what the contractors did. We would like to insulate on the interior, but aren't sure how to go about doing that as we do not want to lose SO much heat into the foundation, we don't want to do this wrong as we don't want our foundation to crumble in the future because of our lack of knowledge regarding this. They did not put foam insulation around the exterior of the foundation, and we don't think the contractors are planning on putting insulation in the room they are doing, however we would like them to if they're supposed to. We're not quite sure if they are taking shortcuts on certain things or not. Of course we would like our house to be as efficient as possible, and would appreciate if someone with knowledge on this subject could help us with the problem of insulating the lower portion of our basement wall. Do we really need to insulate, or is the vapor barrier enough?