A 6-mil polyethylene vapor retarder must be placed between the base course or subgrade and the concrete floor slab, with joints lapped a minimum of how many inches?

In construction, when installing a vapor retarder, it is crucial to ensure that the joints are adequately lapped to prevent moisture from penetrating through the seams. A 6-mil polyethylene vapor retarder is typically specified to control moisture diffusion from the subgrade into the concrete slab.

The requirement to have the joints lapped a minimum of 6 inches is established by building codes and guidelines, which aim to ensure effective moisture control. This lap size allows for sufficient overlap, minimizing the risk of moisture migration, while also accommodating any potential movement or settling in the materials. Proper installation is essential to maintain the integrity of the vapor barrier and protect the concrete from moisture-related issues.

It's important to adhere to these guidelines for optimal performance of the vapor retarder and long-term durability of the concrete slab, as any shortcuts in this aspect can lead to significant moisture-related problems later in the life of the structure.