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Greenmtn
Moisture in exterior side of wall

Hi, I am in the middle of demolition of a bathroom remodel. When I took the wall board/sheetrock off, the wall board was in good condition and not wet. Next was a 6 mil poly vapor barrier with no moisture on poly. I can see the pink unfaced insulation was discolored with mold like colors. Once I pulled the insulation off the cold side of insulation was very wet and the exterior sheeting was wet and cold to touch. The walls studs were not wet or discolored. This bathroom was only used for baths (4 days/week) in the past six years and does not have a bathroom vent. What caused the moisture? Do not want to rebuild until I understand what caused the problem. My guess is the vapor barrier did not allow the wall to breath.

More details: The wood was discolored but still solid with no rot, very surprising considering how wet it was. The vapor barrier and insulation have no gaps and appeared to be installed correctly. The walls are 2 X 4 construction and the house was built in the 70's. I live in Vermont and we just had a period of cold weather followed by a general warming when I started demolition.

canuk
Re: Moisture in exterior side of wall
Greenmtn wrote:

Hi, I am in the middle of demolition of a bathroom remodel. When I took the wall board/sheetrock off, the wall board was in good condition and not wet. Next was a 6 mil poly vapor barrier with no moisture on poly. I can see the pink unfaced insulation was discolored with mold like colors. Once I pulled the insulation off the cold side of insulation was very wet and the exterior sheeting was wet and cold to touch. The walls studs were not wet or discolored. This bathroom was only used for baths (4 days/week) in the past six years and does not have a bathroom vent. What caused the moisture? Do not want to rebuild until I understand what caused the problem. My guess is the vapor barrier did not allow the wall to breath.

More details: The wood was discolored but still solid with no rot, very surprising considering how wet it was. The vapor barrier and insulation have no gaps and appeared to be installed correctly. The walls are 2 X 4 construction and the house was built in the 70's. I live in Vermont and we just had a period of cold weather followed by a general warming when I started demolition.

That's not the role of the vapour barrier.
The barriers role is to prevent vapour entering the wall cavity and condensing --- such as you've discovered.

It's hard to say what the discoloration you see on the insulation. It may actually be dirt which indicates there is moving air happening within the wall cavity.

Somewhere there is a break in the vapour barrier and as a guess it may be behind the tub. It's not uncommon to find the vapour barrier isn't properly sealed to the wall behind the tub.

Another place is the ceiling to wall joint of the vapour barrier ---- if the ceiling has an attic directly above.

The fact there isn't a bath exhaust fan contributes to an increase of vapour drive from the increased moisture in the bathroom.

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