What is the difference between a vapor barrier and a vapor retarder?
To be considered a vapor barrier, testing results from ASTM F 1249 or ASTM E 96 must state a permeance of less than 0.01 perms (grains/[hour * ft2 * in. Hg]) A vapor retarder is classified by ASTM E 1745...To be considered a vapor barrier, testing results from ASTM F 1249 or ASTM E 96 must state a permeance of less than 0.01 perms (grains/[hour * ft2 * in. Hg])
A vapor retarder is classified by ASTM E 1745 as a plastic material having a permeance of less than 0.3 perms as tested by ASTM F 1249 or ASTM E 96.
Though it is true that many people in the construction industry will use these terms synonymously, there is a very big difference between the two. A vapor barrier needs to have a low enough permeance to mimic the permeance of a floor covering. Otherwise the potential exists for the buildup of relative humidity/dew point within the slab/under the floor covering.