To supersede the requirements for a rated fire separation as stated in Sentences 9.10.9.13.(1), 9.10.9.14.(1) and 9.10.9.14.(3) and not require a fire resistance rating, if certain conditions are met [i.e. smoke-tight barrier of not less than 12.7 mm gypsum board is installed on both sides of walls and on the underside of floor-ceiling framing separating a dwelling unit from another dwelling unit, ancillary space or common space in a house with a secondary suite], on the basis that construction of rated fire separations may be cost-prohibitive and the reduction in protection from spread of fire is off-set by more stringent requirements for notification of occupants.
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, which could lead to harm to persons in the other dwelling unit or space.