Purpose of Vapor Barrier in Concrete Slabs

What is Vapor Barrier?

  • A plastic sheet that is placed between the base and the concrete slab.
  • Always placed beneath the rebar or wire mesh and on top of the gravel base.
  • The sole purpose of the vapor barrier is to prevent moisture from penetrating through the concrete.

When to Apply Vapor Barrier:

  • The application of vapor barrier in exterior concrete is unnecessary due to the fact that water penetration does not matter.
  • Any slab on grade that is enclosed and on the interior of a building should have a vapor barrier installed prior to pouring concrete, especially if flooring will be applied.

Vapor Barrier Thickness:

  • Vapor Barrier comes in multiple thicknesses, ranging from 6 to 20 millimeters (mil).
  • 6 mil vapor barriers are specified for most residential concrete projects.
  • T10 to 20 mil vapor barriers are specified for most commercial projects.
  • Check with your local codes department before using vapor barrier on a residential project or check with the project architect or engineer for commercial projects.

Other Relevant Information Regarding Vapor Barriers:

    • Most vapor barriers come in 1,500 square foot rolls.
    • A vapor barrier tape is used to connect multiple sheets of vapor barrier together for larger slabs and utility penetrations. Make sure to use an approved vapor barrier tape that meets permeability standards with that of the vapor barrier.