What fire-rated materials does Ontario code require for a finished basement?

The Ontario Building Code requires all insulation and combustible materials in a finished basement to be covered by a minimum 15-minute thermal barrier, which is most commonly achieved with 1/2-inch regular drywall on walls and ceilings. This basic requirement applies to every finished basement in Ontario, whether it is a simple rec room or an elaborate multi-room finishing project. The requirements become significantly more stringent if you are creating a secondary suite or accessory dwelling unit.

For a standard single-family basement finishing (no secondary suite), the fire-rated material requirements are relatively straightforward. All exposed insulation — whether spray foam, rigid foam board, or fibreglass batts — must be covered by that 15-minute thermal barrier. Standard 1/2-inch drywall meets this requirement for walls and ceilings throughout the basement. The purpose is to prevent insulation materials, particularly foam-based insulation, from being directly exposed to fire, as they can release toxic gases when they burn. Spray foam insulation is particularly important to cover immediately, as some formulations are flammable and produce dense black smoke — leaving spray foam exposed in a finished space violates code and is a serious safety hazard.

Smoke and carbon monoxide detectors are required on every level of the home including the basement, outside all sleeping areas, and inside every bedroom. In a finished basement, this typically means at least two detectors — one outside the sleeping area and one in each bedroom. All detectors must be interconnected so that when one alarm sounds, all alarms in the house sound simultaneously. This can be achieved with hardwired detectors (which require an ESA-Licensed Electrical Contractor) or wirelessly interconnected units. Battery-only detectors are no longer permitted for new installations in Ontario.

The fire separation requirements escalate dramatically for secondary suites. If you are creating a basement apartment, in-law suite, or any self-contained living unit with its own kitchen and bathroom, the Ontario Building Code requires a 1-hour fire-rated separation between the secondary suite and the rest of the house. This means the ceiling assembly separating the basement from the main floor must achieve a 1-hour fire resistance rating — typically two layers of 5/8-inch Type X fire-rated drywall on the basement side of the ceiling joists, with all penetrations (pipes, ducts, electrical boxes) properly fire-stopped with approved fire-stop caulking or putty pads. The walls separating the suite from any common areas or the rest of the house also need 1-hour fire-rated assemblies.

All doors between a secondary suite and the rest of the house must be fire-rated doors (minimum 45-minute rating) equipped with self-closing hardware — the door must close automatically when released. Standard hollow-core interior doors do not meet this requirement. Fire-rated doors are solid-core units with specific certifications and typically cost $300-$800 per door installed, compared to $100-$250 for a standard interior door.

Fire-stopping is required at every penetration through a fire-rated assembly — everywhere a pipe, duct, wire, or cable passes through a fire-rated wall or ceiling. This means using approved fire-stop caulking (rated for the specific penetration type), putty pads around electrical boxes, and fire dampers in ducts that pass through fire-rated assemblies. Fire-stopping is one of the most frequently missed details in basement renovations and one of the first things a building inspector will check. Properly fire-stopping a secondary suite basement renovation typically adds $500-$2,000 in materials and labour to the project.