To supersede the requirements of Sentence 3.2.3.17.(1), which would otherwise require a canopy, if certain conditions are met [the exterior wall of the upper storey is recessed not less than 1 m behind the exterior wall containing the opening in the lower storey]. This [the wall recessing] is to limit the probability of the spread of fire from one storey to the storey above through openings in the exterior wall during the time required for emergency responders to perform their duties, which could lead to damage to the building.