T10 to 20 mil vapor barriers are specified for most commercial projects.
Check with your local codes department before using vapor barrier on a residential project or check with the project architect or engineer for commercial projects.
Other Relevant Information Regarding Vapor Barriers:
Most vapor barriers come in 1,500 square foot rolls.
A vapor barrier tape is used to connect multiple sheets of vapor barrier together for larger slabs and utility penetrations. Make sure to use an approved vapor barrier tape that meets permeability standards with that of the vapor barrier.