Ontario Building Code 2024: Unprotected Opening Limits and Exposing Building Face
Sarah's Expert Insight
OBC Compliance Specialist
"Utilizing the sprinklered opening allowances in Tables 3.2.3.1.-D and E is a 'game-changer' for urban infill projects in London and Oakville, as it allows us to maximize glazing and natural light even on narrow lots. At empcontracting.ca Inc., we emphasize early-stage calculation of the Exposing Building Face to ensure our Muskoka cottage designs or London commercial builds satisfy fire safety without sacrificing the architectural aesthetic our clients expect."
In the 2024 Building Code Compendium, specifically Section 3.2.3.2. and associated tables, the regulation of fire spread between buildings is managed through strict limits on 'unprotected openings' (such as windows and doors). Understanding these requirements is essential for any major development managed by empcontracting.ca Inc. your construction contractor in London, Ontario.
Defining the Area of Exposing Building Face (Article 3.2.3.2.)
According to Article 3.2.3.2., the area of an exposing building face is calculated as the total area of the exterior wall facing one direction on any side of a building. This measurement is taken from the finished ground level to the uppermost ceiling. This calculation is the primary variable used to determine the allowable percentage of glazing based on the distance to the property line, known as the Limiting Distance.
Unprotected Opening Limits for Sprinklered Buildings
The 2024 OBC provides relief for buildings that are sprinklered throughout, allowing for larger window areas closer to property lines than would be permitted in non-sprinklered structures. These limits are divided by occupancy type:
Occupancy Groups A, B, C, D, and F-3 (Table 3.2.3.1.-D)
For residential (Group C), office (Group D), and assembly (Group A) buildings, Table 3.2.3.1.-D dictates the maximum percentage of unprotected openings. For example, a building with an exposing face of 40m² and a limiting distance of 4 meters is permitted to have up to 64% of that face consist of unprotected openings, provided the building is fully sprinklered.
High-Hazard Mercantile and Industrial Occupancies (Table 3.2.3.1.-E)
For Group E (Retail) and Group F Divisions 1 and 2 (High and Medium Hazard Industrial), the restrictions are more stringent due to the higher fire load. Even with sprinklers, these buildings require a greater limiting distance to achieve the same percentage of unprotected openings as residential structures, ensuring that fire spread risks are mitigated in industrial settings.
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.