Concrete Slab Vapor Barrier Placement

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.

Concrete slab vapor barrier placement.

Resistance to water vapor transmission manufacturers typically use one of three terminologies to describe the water vapor transmission. 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. Because extruded polystyrene insulating board will absorb little moisture the vapor barrier can be placed above or below the slab insulation. We have a system that has worked well for us in the past.

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. Details that thermally isolate the slab edge from the foundation wall and outdoors appear to work the best. In nonproblem areas we have traditionally used 6 mil polyethylene film directly under concrete slabs and over a granular fill on the subgrade. 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.

For a vapor barrier below a concrete floor slab most choose 6 to 10 mil polyethylene. In general place the concrete slab directly on top of the vapor barrier with the subbase below.