Understanding OBC 3.1.5.5: Rules for Combustible Cladding and Exterior Wall Components in Noncombustible Buildings
Sarah's Expert Insight
OBC Compliance Specialist
"Navigating the nuances of combustible cladding requires a balance between modern design and strict fire safety adherence, especially for high-density projects in London or lakeside builds in Muskoka. At empcontracting.ca Inc. your construction contractor in London, Ontario, we emphasize that while the OBC allows for aesthetic flexibility, the CAN/ULC-S134 testing and vertical separation rules are non-negotiable for ensuring project approval and occupant safety."
Navigating the complexities of the 2024 Ontario Building Code (OBC) is essential for any major development. When dealing with noncombustible construction, specific provisions under Sections 3.1.5.4 through 3.1.5.6 dictate how and where combustible materials like glazing, sashes, and cladding can be utilized. At empcontracting.ca Inc. your construction contractor in London, Ontario, we ensure every detail of your exterior wall assembly meets these rigorous safety standards.
3.1.5.4. Combustible Glazing and Window Sashes
The code allows for combustible glazing provided the flame-spread rating does not exceed 150 and the aggregate area is limited to 25% of the wall area for that storey. This is typically permitted in buildings not exceeding one storey, or in taller buildings that are fully sprinklered or feature specific vertical separations to prevent fire spread.
Window Frames in Noncombustible Construction
According to Article 3.1.5.4.(5), combustible window sashes and frames are permitted even in buildings required to be of noncombustible construction, provided they are vertically non-contiguous between storeys to mitigate the risk of exterior fire leapfrogging.
3.1.5.5. Combustible Cladding on Exterior Walls
Combustible cladding is a popular choice for modern aesthetics, but it must satisfy strict criteria under Sentence (1). It is generally permitted if the building is no more than three storeys tall or is fully sprinklered. Crucially, the assembly must pass the CAN/ULC-S134 standard fire test, which monitors flame spread and heat flux.
Fire-Retardant-Treated Wood
For projects incorporating fire-retardant-treated wood cladding, the OBC requires accelerated weathering tests (ASTM D2898) before fire exposure testing to ensure long-term safety performance in Ontario's varied climate.
3.1.5.6. Combustible Components in Exterior Walls
Other combustible components within the wall assembly are permitted under similar height and sprinkler constraints. These components must either pass the same fire testing as cladding or be protected by at least 25 mm of masonry or concrete cladding. Consulting with empcontracting.ca Inc. your construction contractor in London, Ontario, helps developers navigate these technical requirements during the design phase.
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.