Welcome to the forums, JP! The foamboard warms the cavity and is the first condensing surface in the insulation make-up. Using only 1" (R-5) rigid, may not be enough to limit condensation for the three lowest temperatures in your area. Eg.- using Lebanon as your city- average lows of Jan., Feb., and Dec. = 24* http://www.usclimatedata.com/climate...ation=USVA0426
At 7o* inside temp, your inside face of the f.b. would be 37* with 1"
(R-5), giving you condensation there at anything above 29% RH
in the room. This is with cavity insulation of R-13.
At 70* w. 2"fb
(R-10), the RH will be 40%
and above for condensation. If you do use water-resistant drywall, the framing requires 12" o.c. for the ceiling. I would not use it in a basement environment. Dryloc is optional though it will direct the wall moisture to the wall/slab joint (from gravity) to show as pooling rather than letting it through the f.b. in a controlled manner, same with the foil-faced f.b. Roxul is good. Use a foam sill-sealer under the p.t. (code required) bottom plate for an air/thermal/capillary break from the cold/wet slab; http://www.greenbuildingadvisor.com/...-building-code
Use f.b./canned foam, not air-permeable insulation as f.g. or Roxul on the rim joists to stop air infiltration/exfiltration and condensation problems there; http://www.buildingscience.com/docum...l_seal_rev.pdf
See; Calculating shrinkage" in sidebar, pp. 51: http://books.google.com/books?id=iwS...rafter&f=false
Thick enough foamboard will let moisture through without condensing in the cavity, you can use a vapor barrier if; http://www.buildingscience.com/docum...study-analysis