← Ontario Building Code FAQ
OBC DIVISION B · PART 3 · SECTION 3.1 — APPLICATION

Which buildings fall under Part 3 of the Ontario Building Code?

Part 3 applies to buildings exceeding 600 m2 in building area or three storeys in building height, and to all buildings containing Group A (assembly), Group B (care or detention) or Group F Division 1 (high-hazard industrial) major occupancies.

Code reference
The Code directs buildings to Part 3 based on size and use: any building over 600 m2 in building area or more than three storeys, plus every building with a Group A, Group B or Group F Division 1 major occupancy, must be designed to Part 3 regardless of size.
OBC Division A, Subsection 1.1.2.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

The Part 3 versus Part 9 split is one of the first decisions on any project because it drives fire protection, structural review requirements and professional design obligations. Watch for triggers that pull a small building into Part 3, such as a daycare or restaurant occupancy, and remember that building area and building height are defined terms measured to specific datum lines, not simply gross floor area or number of levels.

Plain language

Big buildings, and any building used for things like assembly halls, hospitals, care homes or dangerous industrial work, follow the stricter Part 3 rules. Smaller houses, shops and offices under three storeys and 600 m2 usually follow the simpler Part 9 rules.

Related questions

How is major occupancy classified under the Ontario Building Code?How are building height and building area determined under the Ontario Building Code?What is a high building under the Ontario Building Code?

Get answers like this for any code question

BUILDAiD Assist searches the building code and answers in plain English with exact citations — in seconds.

Try BUILDAiD Beta

This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.