What fire resistance ratings does the Ontario Building Code require for stucco cladding?

Stucco has long been valued as a fire-resistant cladding, and the Ontario Building Code (OBC) sets specific performance standards that work in your favour if you're considering it for your Ottawa home.

OBC Fire Resistance Requirements for Exterior Cladding

Under OBC Part 9 (residential construction), exterior cladding on homes within 1.2 metres of a property line must achieve a minimum fire-resistance rating. Traditional three-coat Portland cement stucco applied over metal lath on a code-compliant substrate typically provides a 1-hour fire-resistance rating, which satisfies OBC requirements for most residential exposing building faces.

For homes set further back from property lines — which is common across Ottawa neighbourhoods like Kanata, Barrhaven, and Orleans — the code is more lenient on cladding fire performance, but stucco still delivers excellent protection. A standard 7/8-inch (22 mm) three-coat stucco application is classified as noncombustible under CAN/ULC-S114, meaning it won't contribute fuel to an exterior fire.

Key OBC provisions to understand:

• Spatial separation (OBC 9.10.15) — When your exterior wall is close to a lot line, the cladding and wall assembly must meet prescribed fire-resistance ratings. Stucco easily satisfies these.- Combustibility requirements (OBC 9.10.14) — Noncombustible cladding is required in certain exposing building face scenarios. Cement-based stucco qualifies; however, EIFS (acrylic-based) systems with EPS foam insulation boards are considered combustible assemblies and may require additional fire-stop detailing.- Fire blocking within the wall cavity — Regardless of the stucco type, the OBC requires fire stops at floor lines and around openings to prevent flame spread within the drainage cavity behind the cladding.

In Ottawa, where semi-detached homes and townhomes in areas like Centretown and the Glebe share party walls, fire-resistance ratings matter even more. If your home shares a wall or is within 1.2 m of a neighbour, your contractor should confirm the full wall assembly — not just the stucco layer — meets the rated requirement.

One practical note: if you're choosing between traditional cement stucco and an EIFS (synthetic) system, be aware that EIFS requires tested and listed assemblies with specific fire-stop details to meet OBC. Many Ottawa contractors install EIFS systems that have been fire-tested to CAN/ULC-S134, which measures fire propagation on exterior walls. Budget roughly $12–$16 per square foot for a code-compliant EIFS installation in Ottawa versus $10–$14 per square foot for traditional stucco, with fire-stop detailing included.

Always ask your contractor for documentation confirming the assembly's fire-resistance rating and ensure the building permit reflects the correct wall assembly for your setback distance.

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• Justyn Rook Contracting
• RenoMotion Inc.
• Titley Construction
• Floor-2-Wall Inc
• Capital City Drywall

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