What is the mil rating of a vapor barrier that must be installed under concrete slab?

The mil rating of a vapor barrier refers to its thickness, where one mil is equal to one thousandth of an inch. For vapor barriers used under concrete slabs, a common requirement is a minimum thickness of 6 mil. This is because a 6 mil vapor barrier is effective at reducing moisture transmission from the ground into the building, which is crucial for preventing issues like mold growth, structural damage, and deterioration of flooring materials.

While thicker barriers (like 8 mil or 10 mil) may provide additional protection and durability, the 6 mil option meets the standard requirements for most construction practices, making it both a practical and cost-effective choice. Thus, in situations where compliance with building codes and ensuring moisture control are essential, the 6 mil vapor barrier is generally the appropriate selection.