What should be done if 90% or more of the soil of the crawl space is covered with a Class 1 vapor barrier?

The reasoning behind dividing the square footage of the soil by 1500 when 90% or more of the soil in the crawl space is covered with a Class 1 vapor barrier is related to the calculation of the ventilation or dehumidification requirements for that space. The use of a Class 1 vapor barrier indicates a high level of moisture control, which allows for a greater area of soil to be addressed in a standard calculation for required airflow or other environmental controls.

This division helps to ensure that the measures taken for moisture management are optimized based on the effective area that still influences the environment underneath the structure. The standard of dividing by 1500 specifically accommodates the reduced impact of the vapor barrier, effectively accounting for the fact that much of the ground moisture is being controlled.

In other options, dividing by smaller figures such as 1000 or 500 would suggest a greater need for intervention when the presence of a Class 1 vapor barrier actually mitigates the moisture issues significantly. Counting the square footage twice would not logically follow any established guidelines for this kind of calculation, as it would inaccurately overstate the area and potentially lead to mismanagement of ventilation or dehumidification strategies.