The requirements for crawl space ventilation openings are cover in Section R408. The crawl space is also referred to as "Under-Floor Space".
The ventilation opening requirements are listed in section R408.2. and are as follows; " The minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 150 square feet (14 m2) of under-floor area. One ventilation opening shall be within 3 feet (915 mm) of each corner of the building. Ventilation openings shall be covered for their height and width with any of the following materials provided that the least dimension of the covering shall not exceed ¼ inch (6.4 mm):
Exception: The total area of ventilation openings shall be permitted to be reduced 11,500 ⁄of the under-floor area where the ground surface is covered with an approved Class 1 vapor retarder material and the required openings are placed to provide cross ventilation of the space. The installation of operable louvers shall not be prohibited.
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