Exterior walls shall not exhibit sustained flaming where tested in accordance with NFPA 268. Where a material is intended to be installed in more than one thickness, tests of the minimum and maximum thickness intended for use shall be performed.
Exception: Assemblies protected on the outside with one of the following:
- A thermal barrier complying with Section 2603.4.
- A minimum 1-inch (25 mm) thickness of concrete or masonry.
- Glass-fiber-reinforced concrete panels of a minimum thickness of 3/8 inch (9.5 mm).
- Metal-faced panels having minimum 0.019-inch-thick (0.48 mm) aluminum or 0.016-inch-thick (0.41 mm) corrosion-resistant steel outer facings.
- A minimum 7/8-inch (22.2 mm) thickness of stucco complying with Section 2510.
- A minimum 1/4-inch (6.4 mm) thickness of fiber-cement lap, panel or shingle siding complying with Section 1404.16 and Section 1404.16.1 or 1404.16.2.