S.C. Code Regs. 8-1221. IRC Section R408.3 Unvented Crawl Space

For unvented under-floor spaces, the following items shall be provided: 1. Exposed earth shall be covered with a continuous vapor retarder meeting ASTME 1745 Class A. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend not less than 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall or insulation. 2. One of the following is provided for the under-floor space: 2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) of crawl space floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.11 of this code. 2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47L/s) for each 50 square feet (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with the S.C. Energy Codes. 2.3. Plenum in existing structures complying with Section M1601.5, if under-floor space is used as a plenum. 2.4. Dehumidification sized in accordance with the manufacturer’s specifications.