Class C FRP and the Ontario Building Code: What §3.1.13 Actually Requires

What §3.1.13 Actually Says

Division B, Part 3 of the Ontario Building Code regulates large-building construction. Section 3.1.13 is the part everyone references but few read carefully. It governs the flame-spread rating and smoke-developed classification of interior finishes — meaning anything you stick to a wall or ceiling that is exposed to the room. FRP panels installed on the interior face of a commercial kitchen wall fall squarely under this section.

The code does two things. First, it sets numerical limits on how fast flame can travel across a finish and how much smoke that finish produces while burning. Second, it tells you which limit applies based on where the finish is installed.

Flame Spread and Smoke Developed, in Plain English

Both numbers come from the same standardised test, performed in Canada under CAN/ULC-S102 (or its American twin, ASTM E84). A 25-foot panel is mounted in a horizontal tunnel, gas burners are lit at one end, and a measured airflow pushes flame down the panel. Two things get recorded: how far the flame travels in a fixed time (the flame spread index, or FSI), and how much smoke is produced (the smoke developed index, or SDI).

• Class A: FSI 0–25, SDI 0–450
• Class B: FSI 26–75, SDI 0–450
• Class C: FSI 76–150, SDI 0–450 (Ontario typically holds SDI ≤ 300 for finishes)

Lower is better, but “better” is not always required. The code asks for the rating that matches the risk of the room.

Where Each Rating Is Required (Common Occupancies)

This table covers the common cases. Always check with your local Building Department and reference the current edition of the OBC for your specific project — sprinklered vs non-sprinklered status changes some of these.

Why Class C Covers Most FRP Jobs in Ontario

The reason most FRP installations in the GTA spec out as Class C is that the rooms FRP belongs in — commercial kitchens, food prep, processing, car washes — are not exit routes and not assembly spaces over the size thresholds. They are working rooms. The code recognises that a working room with a sprinkler system and a clear path of egress does not need the same finish rating as a stairwell people are running down during an alarm.

Specifying Class A FRP when Class C is allowed costs you more money for no compliance benefit. It is one of the most common ways money gets wasted on a fit-out.

What Inspectors Actually Ask For

When a Building Inspector or Public Health Inspector shows up to sign off on an FRP wall, they want three things in hand:

1. A current CAN/ULC-S102 or ASTM E84 test report from the panel manufacturer showing the FSI and SDI numbers for the exact panel being installed.
2. The manufacturer's installation instructions — confirming the panel was installed in the same configuration it was tested in (substrate, adhesive, joint treatment).
3. Confirmation that the rating matches the occupancy classification assigned to the room by the building's permit drawings.

If any of these are missing, the inspection fails. Keep the test reports on file at the site for the duration of the job.

The “Tested Assembly” Detail That Trips People Up

Flame-spread numbers apply to the panel as tested. If the test report shows the panel was tested glued to 5/8" Type X drywall, but you install it glued to 1/2" OSB, you technically no longer have the same fire performance. Most inspectors are reasonable about this — drywall is more common than OSB as a substrate, and adhesive over drywall is the standard tested configuration — but if you are installing over an unusual substrate, ask the panel manufacturer for a tested-assembly letter.

Smoke Developed Is the Quiet Killer of Bad Panels

Flame spread gets all the attention, but smoke developed is what kills people in a fire. Cheap import FRP panels sometimes meet Class C on flame spread (FSI under 150) but generate enormous amounts of smoke (SDI well over 450). Those panels will not pass Ontario inspection. Always check both numbers, not just the class.

Sprinklered vs Non-Sprinklered Buildings

One detail the OBC bakes into §3.1.13 that is easy to miss: a fully sprinklered building can use a finish that is one class lower than the same space would otherwise require. For example, a public corridor in an A2 occupancy that would normally need Class B finish can drop to Class C if the building is sprinklered throughout. For most modern GTA commercial buildings — which are sprinklered as a baseline — this is the reason Class C FRP shows up in so many spec packages.

Older buildings without sprinklers are a different conversation. If you are doing tenant fit-out work in a non-sprinklered legacy building (common in older parts of Toronto, Hamilton, and Brantford), confirm the sprinkler status with the building owner before locking in the FRP spec. Going from Class C to Class A is not a price change — it is a different product line and sometimes a different substrate detail.

How Corevance Verifies Every Panel

Every FRP panel we install on a commercial job in the GTA comes with the CAN/ULC-S102 test report attached to the quote. The report lists the FSI, SDI, substrate, and adhesive system the panel was tested with. We will not install a panel we cannot show paperwork for. If you have been quoted FRP and the contractor cannot produce the test report, that is a problem before the job even starts.

Questions about whether Class C is sufficient for your specific Ontario project? Call us at 437-849-3781 — we will walk through your occupancy classification with you. For the full CFIA compliance picture alongside OBC §3.1.13, see our CFIA wall system requirements page. For local installation across the GTA, see our FRP installation in Toronto page.