To supersede the requirement for a rated fire separation of exterior walls as stated in Sentence 9.10.12.3.(2) and not require a fire-resistance rating if a 12.7 mm gypsum board is installed on the interior face of exterior walls of each dwelling unit or space referred to in Sentence 9.10.12.3.(1) within the 1.2 m distance.
To limit the probability that fire or smoke will spread from one dwelling unit or space in a house with a secondary suite to another dwelling unit or space through exterior walls, which could lead to damage to the building.