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

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

• A. 4
• B. 6
• C. 1
• D. 2

Answer: (B)

Moisture control under a concrete slab relies on a vapor barrier that limits water vapor moving from the soil into the concrete. The thickness, measured in mils, determines how well that barrier resists punctures and moisture passage. Six mils is the standard minimum because it provides a durable, low-permeability layer that effectively blocks moisture. Thinner options, like four mil, are more prone to damage and allow more moisture through, while very thin barriers (one or two mil) would offer little protection. So the required mil rating is six.

Moisture control under a concrete slab relies on a vapor barrier that limits water vapor moving from the soil into the concrete. The thickness, measured in mils, determines how well that barrier resists punctures and moisture passage. Six mils is the standard minimum because it provides a durable, low-permeability layer that effectively blocks moisture. Thinner options, like four mil, are more prone to damage and allow more moisture through, while very thin barriers (one or two mil) would offer little protection. So the required mil rating is six.