Many architects, engineers, and
builders use a vapor barrier under concrete
slabs, but the location of the vapor
barrier varies. Sometimes the vapor barrier
is placed directly under the slab. In
other cases, a layer of sand or crushed
gravel is placed over the vapor barrier
before the concrete is placed. Each location
affects slab performance; is one better
than the other?
Why Use a Vapor Barrier?
Anyone who's ever damp-proofed a
foundation knows that concrete is permeable.
Water draining down through
backfill material or rising up with a high
water table will eventually make its way
through a concrete wall to the living
The same is true of a slab. A concrete
slab placed in direct