--to the vapor barrier or no vapor barrier question is yes and no. In the November, 1997 issue of The Family Handyman in an article titled How a House Works--Harnessing the Heat Pump in your Attic, their drawing of a traditional flat ceiling house shows no vapor barrier. Their drawing for a cathedral ceiling does show a "continuous air/vapor barrier" between the drywall and insulation. They state that "Roofs begin to weaken and rot when warm, moist air from the rooms below leaks through gaps around plumbing pipes, partition walls, heating ducts and other ""attic bypasses,"" and the moisture condenses on the cold roof sheathing and rafters."
Personally, I do agree that a vapor barrier is the right way to go with a cathedral ceiling that has air rising from "soffitt" vents or metal drip edge vents to the roof peak vents. But I don't have a vapor barrier in the ceiling of my 35 year old house and my daughter does not have one in the ceiling of her 160 year old house. Both these houses are not real "tight" and I really don't want a house that is real tight. The smells from cooking, fumes and smells from painting and similar work in the basement, humidity from showers, dishwashing and other similar things needs a way to get out. It might not be as energy efficient as other houses but I don't have to leave when the teenagers put on a weeks worth of cologne before a date. That's my story and I'm sticking to it.