We are doing a big reno project on our 40 year old 1 story house in a cool, damp west coast climate. The foundation is slab-on-grade, and we are installing new engineered wood in most of the house. We are going to glue the floor to the concrete over a cork underlay and a liquid vapor barrier. One room was an old carport, and the concrete slab there is 3" lower than the rest of the house, and the floor was constructed of 2x4 sleepers with a plywood subfloor on top. There don't appear to have been any moisture problems in the past, but the floor was pretty cold. We plan to re-create the 2x4 sleeper and plywood subfloor, with the cork and engineered flooring on top, but are wondering if it it a good idea to add a layer of rigid foam insulation on top of the concrete slab, and whether there should be a vapor barrier anywhere in this part of the floor (right on the concrete? between plywood and engineered wood?). Any advice? Thanks!