Under the 2024 Ontario Building Code (O.Reg. 163/24), buildings required to be of noncombustible construction face strict limits on cladding materials. Combustible cladding is generally only permitted where the building is not more than three storeys, or is sprinklered throughout — and even then, the exterior wall assembly must be tested and pass under CAN/ULC-S134, the standard fire test for exterior wall assemblies.

This single threshold explains why so many low-rise commercial buildings can use a wider range of finishes, while mid- and high-rise projects are steered toward noncombustible systems such as fire-rated ACM panels, metal panel systems, or HPL with a noncombustible core.

Fire Spread and Spatial Separation Requirements

Beyond combustibility, the OBC ties cladding choice to a building’s spatial separation — the distance between the exterior wall and the property line or another building. Buildings with a limited percentage of unprotected openings on the exposing face may still use tested combustible assemblies, but as that percentage rises, the code requires the wall assembly to meet increasingly strict noncombustibility and fire-test criteria.

In practice, this means:

  • A wall assembly tested to CAN/ULC-S134 must limit flame spread and heat flux to defined thresholds above the test opening
  • Buildings within the scope of the code’s taller-building provisions (generally exceeding 4 storeys) require cladding, and cladding on relevant fire compartments, to be noncombustible
  • Ontario’s Building Code Commission has ruled on real disputes over whether specific assemblies meet these criteria, underscoring that “close enough” isn’t a defensible design position

How Common Cladding Materials Measure Up

Different product categories carry very different compliance profiles:

  • ACM/ACP panels — Available with A2 (noncombustible) or FR (fire-retardant) cores. A2-core panels are typically specified for taller buildings and higher-risk occupancies, while FR-core panels may suit lower-rise, sprinklered projects.
  • HPL panels — Core composition varies by manufacturer; noncombustible-rated cores are available for projects requiring stricter fire classifications.
  • Natural metal panel systems and aluminum/steel siding — Generally classified as noncombustible, making them straightforward choices for taller buildings.
  • Wood composite panels — Typically restricted to lower-rise or sprinklered applications, or used as accent cladding rather than full-building coverage, due to combustibility limits.

Choosing the wrong core or finish for a building’s height and occupancy classification is one of the most common — and most expensive — mistakes in commercial re-cladding projects.

Structural, Moisture, and Energy Requirements Also Apply

Fire performance isn’t the only OBC factor shaping material selection. Part 5 of the Code governs environmental separation, requiring cladding assemblies to manage air, vapour, and moisture control — which is why rainscreen designs and compatible subframe systems matter as much as the panel itself. Structural provisions also require cladding attachment systems to be engineered for the wind and snow loads specific to the building’s location and height.

Ontario’s energy efficiency requirements add another layer, since cladding and its supporting insulation contribute to a building’s overall thermal performance targets. Materials that look identical on a spec sheet can perform very differently once wind load, thermal bridging, and moisture management are factored in.

Working Through Compliance Without Slowing the Project Down

None of this needs to become a bottleneck. The most efficient approach is to bring material selection into the design conversation early, rather than after drawings are finalized:

  1. Confirm the building’s height, occupancy classification, and sprinkler status
  2. Identify which cladding cores and assemblies are viable for that classification
  3. Request manufacturer fire-test documentation (CAN/ULC-S134 or equivalent) for the specific assembly, not just the panel
  4. Coordinate subframe, insulation, and air barrier choices alongside the cladding material
  5. Confirm structural and energy compliance before finalizing the material order

This is exactly where a consultation with BuildSky adds value — matching a building’s code classification to a compliant, budget-appropriate material before commitments are made. For projects already navigating permitting, our guide on OBC permit and compliance requirements for commercial re-cladding covers the process end to end.

Choosing Materials With Confidence

Ontario’s Building Code is detailed, but it’s also predictable once a project’s classification is known. BuildSky works with architects, builders, and property owners across the GTA to select and design cladding systems — including fire-rated ACM panels — that meet OBC requirements without sacrificing the building’s intended look. For a deeper look at how fire ratings are tested and classified, see our article on ACM panel fire ratings.

If you’re planning a re-clad or new build in the GTA, contact BuildSky or call (647) 818-4683 to discuss which materials fit your building’s classification.