Historically, the term “vapor intrusion” was discussed only in association with the most heavily contaminated properties. Now, with the emergence of new stricter guidelines, the United States Environmental Protection Agency (US EPA) and many state regulatory agencies identify vapor intrusion as a major driver on many sites, including those with little to no soil or groundwater contamination. Designing and Installing a vapor intrusion mitigation barrier during construction can reduce or eliminate the threat posed by vapor intrusion. A vapor barrier can increase the value of a building and reduce liability.