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 offset 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.