The crawl space ventilation requirements are cover in Section R408. The crawl space is also referred to as "Under-Floor Space". The ventilation requirements are listed in section R408.1. And are as follows; "The under-floor space between the bottom of the floor joists and the earth under any building (except space occupied by a basement) shall have ventilation openings through foundation walls or exterior walls. 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 space area, unless the ground surface is covered by a Class 1 vapor retarder material. When a Class 1 vapor retarder material is used, the minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 1,500 square feet (140 m2) of under-floor space area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of the building."
If you want to learn more about crawl space ventilation or the International Residential Code requirements for crawl space ventilation please visit our website, or click here and read the complete International Residential Code Section R408 Under-Floor Space.