Moisture problems with vapor barrier – Part 1
I am a home owner building a 2,000 sq ft addition to our home 50 mls. north of NYC, on a small mountain in the Hudson Valley, so it’s colder up here in the winter and less humid than the river valley in the summer. This is a wood frame two story structure without central AC built on an exposed concrete slab floor. We are at finished rough-in stage. This winter, the radiant heat in the slab was first turned on, resulting in a lot of moisture being evaporated from the concrete into the building. Moisture started to drip from between the R38 paper backed fiberglass on the second floor cathedral ceiling and running down the interior plastic sheet vapor barrier. Upon investigation I discovered that the roof sheathing, Styrofoam air vents and top 2″ of insulation were soaking wet, with the bays with least venting around skylights and roof vent pipes being even wetter. The ceiling is vented with typical soffit vents and roof ridge vent. Skylights and pipes have Styrofoam bridging vents around them with 1″ holes drilled in the adjacent rafters. We have now drilled 6 holes for more venting.
The12″ roof sandwich is shingle, roof paper, 1/2″ plywood sheathing, Styrofoam air vents, R38 paper backed fiberglass insulation, plastic sheet vapor barrier and then it will be 1/2″ drywall. The 6″ exterior walls are 5/8″ T1-11, or Stucco on the outside, Tyvec, 1/2″ sheathing, R19 paper backed fiberglass, plastic vapor barrier then it will be 1/2″ drywall.
Now it is above freezing I have opened up the ceiling, drilled more holes in the rafters and provided better rigid foam sheet venting across the skylight headers, called back the roofer to re-do the ridge vent and dried it out. WILL I STILL HAVE MOISTURE PROBLEMS WHEN THIS IS DRY WALLED AND CLOSED UP? Tony
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