How to Use Vapor Barriers on Cathedral Ceilings

Insulating a cathedral ceiling has certain challenges but the basics are the same as with any other ceiling. To keep moisture and mold from forming on your ceiling, the drywall, vapor barrier and insulation must be installed in the correct order. The order, working from the outside in, is insulation, then vapor barrier, then drywall.

Vapor barrier (4 Mil minimum)
Drywall (minimum 5/8")
Staple gun and staples
Fiberglass batting insulation (unfaced)
Insulation supports
Construction adhesive
Tyvek tape
Ladder

Instructions

- 1
  Install fiberglass batting insulation in between roof rafters. Make sure you use unfaced batting. Depending on the pitch of the roof, it may be necessary to use insulation supports in between the rafters to keep the insulation from falling down.
- 2
  Install the vapor barrier by stapling it to the underside of the rafters. Make sure to overlap the seams by a few inches, then tape the seams with Tyvek tape. Seal all top and bottom seams to the rafters with construction adhesive.
- 3
  Install the drywall directly over the vapor barrier, screwing it into the rafters. Make sure the screws go into the wooden rafters. If you miss the rafter, the screw will poke a hole through the vapor barrier and breach the seal made by the vapor barrier
- 4
  Tape, mud, sand and finish the drywall ceiling like you would the walls.

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