Dan writes from Lockport, New York: "Last summer I added a three season room off the back of our house. The floor is a 15 x 25' concrete pad, the walls are all sliding glass with screen doors. There is a regular roof, plywood and 2x10. This spring I plan on hiding the joist by adding a ceiling. Should it be insulated or not?"

Answer: Insulating the ceiling will make it easier to control the temperature in the room - cooler in the summer and warmer in the winter. There are, however, some potential concerns.

1. Ventilation - Whether or not you insulate, having ventilation in the roof should be addressed.

2. Humidity - How will humidity (all three seasons) be controlled?

3. Conditioning - Is this area going to be conditioned, either from the existing house or by adding space heating or cooling? If the space will be conditioned, will it be done with electric or gas (or propane)?

If insulation is to be added, you must answer these questions first and I recommend discussing your answers with a contractor.

If insulation is added, be sure to use a vapor retarder (facing the conditioned space) and have adequate ventilation. To get maximum benefit from the insulation, be sure to seal all gaps and seams - including around light fixtures to prevent air leakage.

If you decide to insulate, I recommend R-30c in the ceiling. You will want to apply our Raft-R-Mate® attic rafter vents first and then apply the R-30c with the paper facing down. After installation, you will want to cover the insulation with sheetrock or another fire-rated board.