Replies

1. 
   Guest_ | Aug 21, 1999 01:15am | #1

   *
   I wouldn't put a vapor barrier in the ceiling(above thecedar anyway). I know of one case where the homeowner thought that because poly was used for sidewalls, it made sense to install it on the ceiling as well. He had enough condensation between the drywall and poly to grow quite mold crop, which stunk up the whole house. The drywall,poly, and insulation had to be removed and new drywall (no poly this time!) replaced.

   If you urethane the cedar, that would put a vapor barrier in the living space, which would be fine. If they want the cedar left natural then don't install a vapor barrier at all.

   John

1. 
   Guest_ | Aug 23, 1999 08:16am | #3

   *The situation John describes is a house with a moisture vapor / ventilation problem, not really a vapor retarder problem. The plastic only made the problem evident, it didn't cause the moisture. Anyway, What you should consider is an air barrier to prevent warm moist air from getting into the 4" vent channel you have. Because as soon as warm moist air gets into that 4" space during the winter (if you are in a cold climate) the moisture will condense. Even 4" of vent space won't stop it. The wood ceiling will have enough joint gaps between along the edges that air will find a way out. Just taping the joints in the foam should serve as an effective air barrier. Maybe a little caulking at the perimeter where foam meets wall too.

2. 
   DAVID_K._KOZIAL | Aug 23, 1999 08:16am | #2

   *
   The currant house that we are building has all cathderal ceilings,we have 16" ijoist for rafters to allow for 12" batt insulation & 4" air space.
   The homeowner wants to go over that with 2" foam, 3/4" air space, then 3/4" t&g cedar.
   Where should the vapor barrior go, is this type of ceiling pron to any promblems. Any advice appreciated!!