Why should polyethylene sheeting and vinyl wallpaper not be installed on the interior side of basement finishes?

Polyethylene sheeting and vinyl wallpaper should not be installed on the interior side of basement finishes primarily because they trap moisture. In basements, where humidity levels can be high due to ground moisture and inadequate ventilation, these materials can create a barrier that prevents moisture from escaping. When moisture is trapped, it can lead to a buildup of water vapor, which increases the risk of mold growth and structural damage as it condenses within wall assemblies.

The presence of trapped moisture can also contribute to unhealthy indoor air quality, resulting in potential health risks for occupants. Therefore, proper ventilation strategies and moisture management techniques are critical when finishing basements to ensure that moisture can dissipate rather than be confined behind impermeable materials. This approach helps to maintain the integrity of the building and the health of its occupants.