The Ontario Building Code | Lateral Stability
188.8.131.52. Lateral Stability
(1) Except as provided in Sentence (2), chimneys shall be braced in accordance with Subsection 4.3.2. to provide stability under wind loads.
(2) Achimney need not be laterally braced provided,
(a) no horizontal outside dimension is less than 400 mm, and
(b) the chimneyextends not more than 3.6 m above a roof or the masonry wall of which it forms a part.