The Ontario Building Code | Noncombustible Construction
188.8.131.52. Noncombustible Construction
(1) In a building required to be of noncombustible construction,
(a) the flame-spread ratings required by Subsection 3.1.5. shall apply in addition to the requirements in this Subsection, and
(b) the flame-spread ratings for exits in this Subsection shall also apply to any surface in the exit that would be exposed by cutting through the material in any direction, except that this requirement does not apply to doors, heavy timber construction in a sprinklered building and fire-retardant treated wood.