How to install vapor barrier on concrete floor. Using a utility knife cut the length long enough to wrap edges up the wall 3 4 inches. 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. Splice each roll of underlayment with a 3 mil tape duct tape or similar pressure sensitive tape that meetsexceeds.
The water vapor transmission ratings suggested by the flooring manufacturer. See below for more discussion on this. Wrap vapor barrier up edge of wall 3 4 inches and tape to wall.
May be higher check job specifications or building codes 4.