The Ontario Building Code | Fire-Retardant Treated Wood Roof Systems
220.127.116.11. Fire-Retardant Treated wood Roof Systems
(1) If a fire-retardant treated wood roof system is used to comply with the requirements of Subsection 3.2.2., the roof deck assembly shall meet the conditions of acceptance of CAN/ulc-S126, "Test for Fire Spread Under Roof-Deck Assemblies".
(2) supports for the roof deck assembly referred to in Sentence (1) shall consist of,
(a) fire-retardant treated wood,
(b) heavy timber construction,
(c) noncombustible construction, or
(d) a combination of the items described in Clauses (a) to (c).