Ontario Building Code Fire Safety: Protecting Exterior Walls and Soffits
Sarah's Expert Insight
OBC Compliance Specialist
"At empcontracting.ca Inc. your construction contractor in London, Ontario, we find that the 1.2-meter rule for corner windows is a common hurdle in modern 'L-shaped' home designs and secondary suite conversions. Whether you are building a custom cottage in Muskoka or a multi-unit dwelling in Oakville, ensuring these fire-rated soffit materials are specified early prevents expensive retrofits during the final inspection phase."
Navigating the 2024 Building Code Compendium is essential for any major residential or commercial project. As empcontracting.ca Inc. your construction contractor in London, Ontario, we focus on the critical fire safety regulations found in Part 9, specifically regarding how fire spreads through exterior openings and roof projections.
OBC 9.10.12.3: Exterior Walls Meeting at an Angle
When exterior walls of a building meet at an angle of 135° or less, the risk of fire jumping from one unprotected opening (like a window or door) to another increases significantly. The Ontario Building Code mandates a minimum horizontal distance of 1.2 meters between such openings when they serve different fire compartments or separate dwelling units in a house with a secondary suite.
Fire-Resistance and Material Requirements
If the 1.2-meter clearance cannot be maintained, the exterior walls must have a fire-resistance rating equivalent to the interior fire separations. For houses with secondary suites where interior walls aren't fire separations, the exterior walls within that 1.2-meter zone must be finished with at least 15.9 mm Type X gypsum board to provide the necessary thermal protection.
OBC 9.10.12.4: Protection of Soffits
Soffits are often a vulnerable point for fire spread into attic spaces. This section applies to any soffit enclosing a projection located less than 2.5 m vertically above or 1.2 m horizontally from a window or door. Protection is mandatory if the soffit spans more than two residential suites or if an upper storey projects beyond a lower storey involving fire separations.
Approved Fire-Protection Materials
According to the code, protection must be provided by specific materials to prevent rapid fire spread into the roof or upper floor assemblies:
- Noncombustible material (min. 0.38 mm thick, melting point above 650°C)
- 12.7 mm gypsum soffit board or wallboard
- 11 mm thick plywood or lumber
- 12.5 mm thick OSB or waferboard
Key Exceptions: Sprinklers and Fire Blocks
The code allows for exceptions to these soffit protection rules if the attic space is completely separated by fire blocks or if the entire building—including the rooms with openings beneath the soffits—is fully sprinklered in accordance with OBC standards.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.