What's the difference between Part 9 and Part 3 buildings in Toronto code?

Part 9 and Part 3 refer to different sections of the Ontario Building Code (OBC) that apply based on building size, height, and occupancy type. Part 9 covers smaller residential buildings, while Part 3 addresses larger, more complex structures with stricter requirements.

Part 9 buildings are typically what most Toronto homeowners deal with - single-family homes, duplexes, and small apartment buildings up to 3 storeys and 600 square meters per floor. This includes most century homes in neighborhoods like Cabbagetown and The Annex, post-war bungalows in Scarborough and Etobicoke, and newer townhomes throughout the GTA. Part 9 allows for more prescriptive, simplified requirements. For example, you can use standard lumber sizing charts for structural elements, and the code provides specific tables for things like joist spans and beam sizes. Most residential renovations - kitchen remodels, basement finishing, additions under 3 storeys - fall under Part 9.

Part 3 buildings are larger or more complex structures that exceed Part 9 limits. This includes buildings over 3 storeys, large commercial spaces, most condominiums, and buildings with floor areas exceeding 600 square meters. Part 3 requires engineered solutions rather than prescriptive tables. You'll need structural engineers, fire protection engineers, and more detailed drawings. The permit process is significantly more complex and expensive, often requiring multiple submissions and reviews.

For Toronto homeowners, this distinction matters most when planning additions or major renovations. If you're adding a third storey to your home, you might trigger Part 3 requirements depending on the total floor area. Similarly, if you're converting a large house into multiple units, you could move from Part 9 to Part 3 classification. Part 3 projects typically require professional design teams and can add $15,000-$50,000+ in engineering and consultant fees compared to Part 9 work.

The permit timeline also differs significantly - Part 9 permits through the City of Toronto typically take 10-20 business days for simple projects, while Part 3 can take 6-12 weeks or longer due to the additional review requirements. Part 3 projects also require more inspections and have stricter fire separation, accessibility, and structural requirements.

When planning any major renovation or addition in Toronto, consult with an architect or designer early to understand which code section applies to your project, as this will significantly impact both cost and timeline.