3.1.11.2.

(1) Except as permitted by Sentence (2), fire stops conforming to Article 3.1.11.7. shall be provided to block off concealed spaces within a wall assembly,

(a) at every floor level,

(b) at every ceiling level where the ceiling forms part of an assembly required to have a fire-resistance rating, and

(c) so that the maximum horizontal dimension is not more than 20 m and the maximum vertical dimension is not more than 3 m.

(2) Fire stops conforming to Sentence (1) are not required provided,

(a) the wall space is filled with insulation,

(b) the exposed construction materials and any insulation within the wall space are noncombustible,

(c) the exposed construction materials and any insulation within the wall space have a flame-spread rating not more than 25 on any exposed surface, or on any surface that would be exposed by cutting through the material in any direction, and fire stops are installed so that the vertical distance between them is not more than 10 m, or

(d) the insulated wall assembly contains not more than one concealed air space, and the horizontal thickness of that air space is not more than 25 mm.