National Occupational Competency Testing Institute (NOCTI) Carpentry Practice Exam

Insulation with a vapor barrier should face towards the interior of the building in an exterior wall. This is because the vapor barrier serves to prevent moisture from the warm interior air from penetrating into the cooler wall assembly where it could condense and lead to potential problems such as mold growth or material degradation.

By installing the vapor barrier on the interior side, it effectively protects the structural elements and insulation within the wall from moisture generated indoors, ensuring that the wall remains dry and maintains its thermal performance. Proper placement of the vapor barrier is crucial in climates where there are significant temperature differences between the interior and the exterior, as it plays a critical role in maintaining indoor air quality and energy efficiency.

In contrast, having the vapor barrier face outward, downward, or toward the exterior would defeat its purpose by allowing moisture to accumulate within the wall assembly.