Shawn writes from Prince Edward Island, Canada: "We are purchasing a home now which has a 12' X 14' sunroom on the back of the house (north side). Currently there is no insulation under the floor - plus there is no skirting around the outside of the sunroom so access is easy to get under to do the job. My question is, what "R Factor" insulation should I use and how to do it, ie vapor barrier etc. Also would I then put plywood on the bottom after the insulation is put between the floor joists. It has electric heat with cathedral ceilings and we would really like to use this space in the winter so we wanna do the insulating correctly."

Answer: The current requirement for floors over an unheated space in PEI is R 28. One way to achieve the required thermal resistance is to fill the spaces between the floor joists with R-20 batts followed by 2" of CodeBord® extruded polystyrene rigid insulation. Seal the joints of the foam sheathing with 4" wide strip of peel-and-stick air barrier membrane to help eliminate air leakage. This will give you a thermal resistance of R-30 and the foam insulation will help eliminate the thermal bridges and will help keep the floor warmer. The vapor barrier needs to go on the warm side. A plywood subfloor with sealed joints can act as a suitable vapor barrier on inside.