Which direction should the vapor retarder face when installing insulation in crawl spaces?

When installing insulation in crawl spaces, the vapor retarder should face toward the conditioned space. This is because the primary function of a vapor retarder is to prevent moisture-laden air from the crawl space from moving into the insulated area above, which is usually a living space. By placing the vapor retarder toward the conditioned area, it helps to manage and control humidity levels, thereby reducing the risk of condensation forming within the insulation or on ceiling surfaces.

If the vapor retarder were to face away from the conditioned space, moisture could penetrate the insulation and potentially lead to issues such as mold growth, wood rot, or degradation of the insulation material itself. Proper installation of the vapor retarder creates a barrier to moisture migration, which is crucial for maintaining the integrity of both the insulation and the overall structure of the building.