A. Clayton DeKorne responds: The poly isn’t the problem. Moisture in wall cavities is only a problem if it condenses into liquid water. To condense on the poly, the humidity would have to be very high (over 50% relative humidity), and the poly very cold (due to poor insulation or lots of cold outside air leaking into the wall). In this case, you’ll have condensation problems, with or without poly.
To understand this, let’s look at a few principles. Vapor retarders, such as poly, are installed on the warm side of walls to prevent moisture diffusion into the wall cavity where it can condense-and cause moisture damage. Diffusion is the movement of moisture through the tiny pores in a material and is only a problem in homes with high indoor...
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