(1)
Except as permitted by Sentences (2) and 3.1.10.3.(2), a firewall shall extend above the roof surface to form a parapet not less than
(a)
150 mm high for a firewall required to have a fire-resistance rating not less than 2 h, and
(b)
900 mm high for a firewall required to have a fire-resistance rating not less than 4 h.
(2)
A firewall that separates 2 buildings with roofs at different elevations need not extend above the upper roof surface to form a parapet, provided the difference in elevation between the roofs is more than 3 m.