Is the lack of a vapor barrier in the attic causing the mold issue

atticmoldvapor-barrier

For the last couple of days we have noticed more and more mold growth on the ceiling throughout the house. Wondering what was going on, I climbed into the attic this past weekend and notice that no vapor barrier was ever put in place along with an inadequate level of insulation. I plan on blowing in the additional insulation to bring the home up to the recommended levels, but what can be done in regards to the missing vapor barrier?

Update: I live in central Wisconsin. I am seeing the mold in the living area of the house mostly around the can lights.

Best Answer

Moist air is condensing (barring any oughtright leaks) It is most likely due to air leakage from house to attic:

  • Ceiling to attic is leaking moist air, condensing. Solution: air sealing of all penetrations (light fixtures, ducting, electrical, gaps in construction)
  • Insufficient insulation, combined with air leakage allows condensation to occur. Vapor barrier (VB) insulation (batt with paper facing) should NOT be placed OVER any existing insulation, creating a trap. If used, the VB is placed against the heated side in winter. Do not use poly for a vapor barrier. The assembly must be able to dry in either direction, should condensation occur.

Update RE can lights Recessed cans are notorious for leakage. If they are IC rated (designed for direct insulation contact) they can be air sealed with a ASTME 136 rated firecaulk directly. If they are non-IC, a XPS box can be built that meets the clearance requirements of the fixture (insulation must be a minimum of 3" around a non-IC fixture (NEC 410.66)) Many commercial products exist for covering cans.

Video: Airsealing recessed lighting by Green Homes America

I've seen this condition develop when a bath vent fan was dumping air directly into the attic and it saturated the insulation and it grew mold down through the drywall.

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