We are in the process of finishing our 1000 sf basement. All the walls are up, plumbing is in, and all that is left is a bit of drywall sanding, painting and laying of flooring (I plan to finish the drywall & painting this spring). Got a good deal on some engineered wood flooring last year, so that's been acclimating in the basement for about 3 months, and the Shaw Selitac should be here next week.

Question: Should we still lay the 6 mm vapor barrier under the Selitac? Any reasons NOT to?

Background: We live in East Tennessee, and there is some amount of humidity that comes up from the slab. The Selitac is supposed to take care of that (and we will, of course, tape the seams with the polyethylene duct tape). When we didn't run the dehumidifier in the basement last year and turned off our A/C during a poorly timed vacation, there was a small amount of mold on the baseboards. Understandable, since the humidity in the basement was almost 80% when we got back from vacation due to record-setting rainfall in July--it rained almost every day for 3 weeks while we were gone. Of course, hindsight is 20-20, and we realize we should have left the A/C and dehumidifier on. Took care of the mold issue with a buckets of stuff from Home Depot that turned the concrete and baseboards white, and the humidity has been at or below 40% since last August thanks to the dehumidifier and decrease in precipitation.

Anyway, the point is that I want to make sure my basement floor is as impervious to moisture as possible since I and my daughters all have mold allergies and I am laying the floor myself this summer in my "spare time."

Thoughts? Suggestions?