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A friend of mine has just built a log house with standard 2x4 (or 2x6) wall framing on the second floor in zone 6-7. The walls and ceiling have been insulated (roxul and foam in the walls and pink in the ceiling) but they have not yet put up a polyethylene vapor retarder. They turned on the heat this week and the walls started to drip and the sheathing behind the wall insulation became wet. Essentially, the moisture in the house turned to vapor and quickly condensed on the cold surfaces of the house.
I have told them that they need to either put up a sealed and caulked smart membrane, or an air barrier and ideally a layer of foam on the outer surface of the sheathing (R-10-15) (although they have already installed their rain screen and siding).
I would hate to see them close up their walls with poly (which they intend to do), and I was hoping this forum could provide some great advice that they could feel confident about. How should they proceed?