If less than 90% of the soil in the crawl space is covered with a Class 1 vapor barrier, what calculation must be performed for ventilation requirements?

When determining ventilation requirements for a crawl space with less than 90% of the soil covered by a Class 1 vapor barrier, the correct calculation involves dividing the square footage of the exposed soil by 150. This ratio is based on established building codes and standards that dictate the amount of ventilation necessary to mitigate humidity and potential mold growth in spaces with significant soil exposure.

By dividing the square footage by 150, you are determining the amount of net free ventilation area required to ensure that the crawl space remains adequately ventilated. The rationale for using this specific factor comes from the need to maintain a balance of air exchange in areas that may accumulate moisture. When a significant portion of the soil is exposed and not covered by a barrier, the risk of moisture buildup increases, making ventilation even more critical.

In contrast, the other calculations listed, such as dividing by 100 or 200, do not align with the established guidelines for assessing ventilation needs in such scenarios. These incorrect factors might lead to insufficient ventilation, risking moisture issues and compromising the structural integrity or health conditions in the crawl space. Hence, using the factor of 150 provides a more appropriate and effective measure for managing air circulation and moisture control in these areas.