To supersede the requirements of Sentence 9.10.11.1.(1), which would otherwise require the party wall to be a firewall, if a certain measure is taken [i.e. the party wall is constructed as a fire separation having not less than a 1 h fire-resistance rating], on the basis that this is restricted to buildings that are limited in height in which evacuation can be expected to be relatively quick.
This [the measure] is to limit the probability that fire will spread from one dwelling unit or house with a secondary suite to another dwelling unit or house with a secondary suite, which could lead to damage to the adjacent building.