Ontario Building Code 2025: Structural Updates & Compliance Guide

The 2024 Ontario Building Code (OBC), which takes effect on January 1, 2025, introduces key updates that reshape how buildings are designed and approved. These updates strengthen structural safety, improve energy performance, and streamline permitting for residential and commercial projects.

This guide highlights the most important changes every engineer, contractor, and homeowner should know.

1. Understanding Your Path: Part 9 vs. Part 4

The single most important concept to grasp is that the OBC provides two different paths for structural compliance. The 2025 updates affect both, but in different ways.

• Part 9: Prescriptive Design. This is the "recipe book" for standard residential construction. It provides pre-calculated tables for joist spans, footing sizes, and wall assemblies.

  
  

• Part 4: Performance Design. This is the "engineering" path. It is used when a design falls outside the scope of Part 9 (e.g., large open-concept floors, tall walls, steel beams, or commercial buildings).

Here’s how they compare:

Feature	Part 9 (Prescriptive)	Part 4 (Engineered)
What is it?	A "recipe book" of pre-calculated tables.	A set of rules for custom engineering analysis.
Who Uses It?	Contractors, builders, and homeowners.	Structural Engineers.
Used For:	Standard houses, decks, and small buildings.	Complex, large, or non-standard buildings.
OBC 2025 Update:	Updated span tables; new energy rules.	Updated load calculations (snow, wind, seismic).

2. Key Updates in the 2025 OBC

The new code introduces several key changes.

• Structural Load Calculations (Mainly Part 4): New regional climate data has led to updated snow, wind, and seismic loads. This directly impacts how engineers in Part 4 must design foundations, roof structures, and lateral bracing.

• Energy Efficiency (Mainly Part 9): This is a major change for residential construction. The new code requires higher minimum RSI-values for insulation in walls, roofs, and foundations, as well as stricter U-values (better performance) for windows.

• Fire Safety Requirements: The code enhances fire protection in multi-unit dwellings and legal suites. Key updates include:

  
  

  • Walls: Minimum 1-hour fire-resistance rating between suites.

  • Floors: Minimum 45-minute fire-resistance rating for floor assemblies separating units.

• Accessibility (AODA): Provisions for accessibility have been strengthened to align more closely with the Accessibility for Ontarians with Disabilities Act (AODA), affecting entrances, washrooms, and circulation paths.

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3. Compliance & Practical Tips

• Consult an Engineer Early: This is the most important step. An engineer can immediately identify if your project fits within the simple Part 9 tables or requires a custom Part 4 engineered design. This avoids costly delays and redesigns.

• Use the Digital Permit System: Ontario’s new electronic permit systems are designed to reduce paperwork and speed up approvals. Submit a complete package, including structural drawings, energy forms, and any required (Part 4) engineering reports.

• Verify Materials Before Installation: Double-check that the insulation, windows, and fire-rated drywall you've ordered meet the new, stricter 2025 OBC requirements.

Conclusion: Navigating the 2025 Code with Confidence

Understanding the 2025 updates isn't optional in Ontario—it's an OBC requirement for safe, compliant, and efficient construction. Knowing the difference between Part 9 (Prescriptive) and Part 4 (Engineered) and coordinating early with an engineer ensures your projects will meet all new structural, energy, and fire safety standards.

At Parsways Inc., we think beyond the blueprints. We ensure your design not only meets the new OBC standards on paper but also stands strong in the test of performance and durability.

Co-authored by Yousef Davari and Negin Amani.