Concrete Slab Vapor Barrier Placement

Aci 302 1 which is an american concrete institute standard for slab construction was modified in the early 2000 s to reflect the change in the placement of the vapor barrier directly below the concrete if a low permeable membrane flooring was to be installed.

Concrete slab vapor barrier placement.

We have a system that has worked well for us in the past. We would like to resolve the question of proper placement of vapor barriers under concrete slabs on grade. The american concrete institute s guide for concrete floor and slab construction recommends that the thickness of the vapor retarder be at least 10 mils. In nonproblem areas we have traditionally used 6 mil polyethylene film directly under concrete slabs and over a granular fill on the subgrade.

See below for more discussion on this. Because extruded polystyrene insulating board will absorb little moisture the vapor barrier can be placed above or below the slab insulation. Resistance to water vapor transmission manufacturers typically use one of three terminologies to describe the water vapor transmission. For a vapor barrier below a concrete floor slab most choose 6 to 10 mil polyethylene.

If the subbase is sharp angular gravel a thin layer of sand can be placed on top of the gravel subbase next to the vapor barrier. Puncture studies of 6 8 10 and 20 mil vapor retarder materials have shown that 10 mils is the minimum thickness that should be considered and thicker material may be necessary over angular base materials.