California Residential Inspector Practice Exam

Which thickness is specified for the moisture barrier covering wood columns in crawl spaces?

1. 10 mil

2. 20 mil

3. 30 mil

4. 40 mil

The correct answer is: 40 mil

The specified thickness for the moisture barrier covering wood columns in crawl spaces is 40 mil. This requirement is in place to ensure maximum protection against moisture intrusion, which can lead to decay and deterioration of the wood columns over time. A thicker barrier such as 40 mil provides increased durability and resistance to punctures, tears, and environmental wear, which are particularly important in the often damp conditions of crawl spaces. The choice of a 40 mil moisture barrier aligns with industry standards, specifically those from the Florida Building Code, which serves as a guideline for materials used in construction across similar environmental conditions. This thickness helps to effectively prevent vapor and moisture from penetrating through to the wood columns, safeguarding their structural integrity. In comparison, lesser thicknesses such as 10 mil, 20 mil, or 30 mil, while potentially offering some level of protection, do not provide the same degree of durability or moisture resistance as the 40 mil option. Therefore, using a moisture barrier that meets or exceeds the 40 mil specification is critical for long-term protection in crawl space applications.