What is the approximate percentage of soil that should be covered by a vapor barrier?

The appropriate percentage of soil that should be covered by a vapor barrier is typically aimed at maximizing moisture control and minimizing the risk of water vapor affecting structural components. A coverage of approximately 90% is recognized as best practice in many construction and building contexts.

Covering 90% of the soil with a vapor barrier provides sufficient protection from moisture migration into the building envelope, thereby reducing condensation problems, mold growth, and other moisture-related issues that can compromise the integrity of the structure and indoor air quality. A barrier that covers a lesser percentage might leave gaps where moisture can penetrate, potentially leading to the aforementioned issues.

Total coverage at 100% might seem ideal, but in practical applications, factors such as installation and environmental considerations can make 90% the most effective balance between effectiveness and practicality. Thus, 90% coverage is often recommended as a standard to achieve optimal moisture control.