David writes from Titusville, Florida: "I live in central Florida. I am retro-fitting an older concrete block home that has a near flat ceiling. Roof joists are 2X8. Roof sheathing is 1/2" plywood. I plan to use R-19 unfaced batts between the joists. I would like to follow that with 3/4" foil faced (on one side) foam board on the joists to get more R value. Then install the dry wall. Do you think this would cause problems?"

Answer: The system you describe has one vapor barrier toward the warm-in-winter side, as we recommend. It should work fine. However, we do not manufacture a foil-faced foam board. I have no data on how that will perform.