The Ontario Building Code | Extension of Buildings of Combustible Construction
11.4.2.6. Extension of buildings of Combustible Construction
(1) The performance level of an existing buildingof combustible construction is reduced where the existing building is extended by adding a storey or storeys such that the extended building will be more than four storeys in building height.
11.4.3. Compensating Construction
In Plain Language
Extending a combustible-construction building by adding a storey or storeys reduces its performance level, as set out in this article, since additional storeys change the fire and structural risk profile the building was originally designed for.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.