Originally Posted by choctaw
Correct, however I don't think you could get it that airtight, we have been doing this for quite a few years with no ill effect. I think the best way would be to put OSB with foil applied to the outside then the vapor barrier on the inside, don't you agree Mike?
I know that Solar Board the manufacturer's instruction say to put the foil to the inside. Why I'm not sure, it doesn't make sense in my head.
Craig, I don't think Alumimum foil would be very cost effective way of lining your walls. Would it help? Yes to a degree but I think you would spend a fortune in Aluminum foil for not that great of savings.
Vapor Barriers - it depends on where you live as to where you put it. Without getting too detailed. Water vapor wants to go from higher pressure to lower pressure. In the South, we are more hot than cold. Hot air can hold more water vapor than cold. Therefore most of the year, the water vapor pressure is higher outside so you put your vapor barrier on the outside of the studs to protect your insulation. The opposite is true for more northern climates. Typically its colder and drier outside than it is inside. The whole point of the vapor barrier is to help protect your insulation from getting wet.
If you double up and put it on both, the potential for water to collect inside the wall is there. Depending on when the walls were installed, would greatly influence the risk.