Contractor suggested applying poly barrier between drywall and insul. AND between the insul and concrete wall up to grade level (have approx. 2.5 feet above grade). Will this create a double barrier that could rot the studs or will leaving the top open between the insul and concrete prevent this? Bottom line, should I apply the second layer of poly against the concrete or forget it?

We are considering adding to our existing home. Someone suggested that we would get the most space for the money by adding a basement (the house is currently on a crawlspace). Can someone give me a very general, ballpark dollar figure for such an addition? THe home is a two story colonial with a crawlspace of approximately 25' x 40'. I would like to raise the house about one or two feet in the process and excavate (on an "ever so slightly" sloped lot) to allow for an outside entrance through a normal door. I would like the foundation walls to be poured, if possible, but block would be okk. I would like to everything necessary to ensure proper drainage (as in a new build). I would like to have the contractors leave the floors unfinished (for me to finish) but to go ahead and hang drywall. I also would like an inside entrance via stairs and "roughed in" plumbing for a future bathroom and wetbar. Any input would be appreciated.