Ceiling Tile as Vapour Barrier?

Q: Do ceiling tiles have the same air barrier qualities as drywall? I have ceiling tiles in the bedrooms on the second floor of my house and I wonder if all my warm air is going right through them into the attic.

A: No. Ceiling tiles don’t have the same ability as drywall to keep warm air in and cold drafts out because there are gaps between each tile. Taped and painted drywall, on the other hand, forms a continuous membrane, and is even permitted as its own vapour barrier in some warmer jurisdictions. Applying a layer of polyethylene plastic beneath the attic insulation (and over the top surface of the ceiling tiles and joists) is the only way to remedy your situation while preserving the tiles. You could also apply a vapour barrier directly to the underside of the tiles, on the ceiling, before applying a new layer of drywall over it all. Prevent migration of warm air into cold areas of your house structure is important not just for energy efficiency, but also to prevent to formation of condensed water and mold.