There is much confusion about how vapor barriers work. For the sake of clarity, consider the following: 1) Polyethylene installed beneath the drywall on the interior side, combined with humid weather. This hinders the wall cavity’s ability to dry, increasing damage. 2) Polyethylene installed beneath the drywall on the interior side combined with cold weather. This is not the solution once held for walls that “won’t hold paint.” Vapor from main source of moisture remains unaddressed. 3) Polyethylene installed outside the drywall, combined with humidity, prevents moisture from diffusion, but not other means. It is important to understand more that climate issues. Look for ways to enhance wall assembly dryness instead of simply avoiding wetness.
Read the full article here: What Happens When You Put a Plastic Vapor Barrier in Your Wall? | GreenBuildingAdvisor.com