Under what condition can crawl space ventilation requirements be reduced to 1 in 1500 sq ft?

The correct answer is based on the requirements set forth in building codes regarding crawl space ventilation. When a crawl space is covered with a vapor retarder and taped, this condition mitigates moisture intrusion significantly. The presence of a vapor retarder acts as a barrier to moisture rising from the ground, which is a primary concern in crawl spaces.

By reducing the need for ventilation to 1 in 1500 sq ft in such scenarios, the building code recognizes that there is less moisture entering the space that would require ventilation to prevent condensation and related issues. This reflects an understanding that proper management of moisture through a vapor retarder can allow for more flexibility in ventilation needs, promoting energy efficiency while still maintaining appropriate building performance.

Other choices, while they may relate to aspects of crawl space management, do not specifically align with code provisions that allow for relaxed ventilation requirements. The installation of insulation, heating of the area, or installation of concrete floors does not inherently provide the same level of moisture control as the outlined condition involving a vapor retarder. Thus, the emphasis on a vapor retarder being properly taped is critical in meeting building code requirements for reducing ventilation needs in crawl spaces.