by Engineer Guy » Wed Aug 04, 2010 9:17 pm
Vapor Barriers are always installed on the habitable side of Insulation. This is to stop warm humidity from the living area from penetrating into the Insulation. Closed cell Foam will likely not be as problematic as Fiberglass or blown-in Insulation. The points made above on ehow.com - and the logic behind Code practices - stand whether it's 70 sq. ft. or 1,700 sq. ft.. Such is Physics.
I'm not predicting dire consequences, but now warm moist air from the living area will meet cooler, drier outside air at the barrier after it penetrates the Insulation. In-wall mold is prevented by having this 'meeting' occur just under the wall covering, be that Drywall, Plywood or Luan, after Insulation moderates the outside air temperature and humidity differential. Some sort of Vinyl-covered interior Wallboard would likely help prevent any problems. Humidity transfer through a Wood Floor might also minimize problems, as might a Fantastic Fan or open windows.
Years ago, a Manufacturer I don't recall came out with pricy interior paint that also served as a Vapor Barrier. It was made for use in older Homes where retrofitting a plastic Vapor Barrier was not practical.
Tyvek, and other exterior House 'wraps' installed under House Siding, 'breathe' to allow humidity transfer while reducing 'wind' infiltration. Interior 6 mil Plastic, and other Vapor Barriers placed just under Drywall, specifically do not breathe or allow humidity penetration. Special Tape is used between plastic pieces to ensure this.
Last edited by
Engineer Guy on Wed Aug 04, 2010 9:33 pm, edited 1 time in total.
~Reality proceeds with or without your consensus~