Insulation, Radiant and Vapor Barriers - Attic insulation:

I’m going to insulate my attic but not sure if the ceiling is o.k. to do? The space is for storage only and the floor has 45 year old insulation with tong and grove flooring down. I would prefer not to tear up the floor. Should I use craft faced insulation with a ventilation space between the roof and insulation? And do I need a vapor barrier on the room side of the insulation. I live in a cold climate.

In northern climates, your goal should be to insulate the living space of the house. Leave roof uninsulated so it can remain the same temperature as the outside. This involves having a vapor retarder over attic floor to prevent flow of warm, humid air into attic where it can condense and cause moisture problems. You should have a free flow of outside air from the eaves of your roof through soffit vents all the way to the gable vents, louver vents, or other type of roof vent. Use baffles to prevent the obstruction of airflow where insulation butts up against rafters or roof sheathing.

Northern climates, an R-value of 49 is recommended for adequate attic insulation. Fiberglass insulation has an R-value of roughly 3.0 per inch of thickness. Cellulose is has an R-value of almost 4.0 per inch. Attic floor will have to be removed to add additional insulation.