What happens if a vapor barrier is incorrectly installed on the cold side?

When a vapor barrier is installed incorrectly on the cold side of insulation, it can lead to significant moisture problems within the wall assembly. The primary function of a vapor barrier is to prevent moisture from passing through it, which is particularly important in colder climates. If the barrier is incorrectly placed, warm, moist air from inside the building can reach the cold surface of the exterior wall, where it may condense. This condensation creates an ideal environment for mold growth, as the trapped moisture provides the necessary conditions for mold spores to thrive.

On the other hand, options that suggest there's no effect on insulation, enhancement of energy efficiency, or protection of the exterior wall fail to recognize the critical role insulation and vapor barriers play in managing moisture and thermal performance. An improperly installed vapor barrier can compromise these functions, ultimately leading to damage to the building materials and potentially impacting the health of the occupants due to mold growth. Thus, understanding the placement and function of vapor barriers is essential for ensuring a healthy and energy-efficient building environment.