2603.5.2 Thermal barrier.
BC § 2603.5.2
Any foam plastic insulation shall be separated from the building interior by a thermal barrier meeting the following provisions, unless special approval is obtained on the basis of Section 2603.9. For exterior walls, foam plastic shall be separated from the interior of a building by an approved thermal barrier of 5/8-inch (15.9 mm) Type X gypsum wallboard or equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to not more than 250°F (120°C) after 20 minutes of fire exposure, complying with the standard time-temperature curve of ASTM E 119 or UL 263. The thermal barrier shall be installed in accordance with criteria established by testing performed in accordance with FM 4880, UL 1040, NFPA 286 or UL 1715, where the thermal barrier shall remain in place for 20 minutes. Combustible concealed spaces shall comply with Section 718 of this code. Exception: One-story buildings complying with Section 2603.4.1.4.
