What are the fire separation requirements between an attached garage and the house under the Ontario Building Code?

The Ontario Building Code takes fire separation between an attached garage and your living space very seriously, and for good reason. A garage stores vehicles, fuel, solvents, and other combustible materials, so the code requires a physical barrier that can resist fire long enough for occupants to escape.

The OBC requires a minimum 45-minute fire resistance rating on the wall and ceiling assembly separating the garage from the habitable areas of your home. In practical terms, this usually means installing 5/8-inch (15.9 mm) Type X fire-rated drywall on the garage side of any shared wall, and on the ceiling if there is living space above the garage. Type X drywall contains glass fibres that hold the board together longer under heat, giving you that critical burn-through delay.

The shared wall must run continuously from the foundation to the underside of the roof sheathing, with no gaps or penetrations that aren't properly fire-stopped. Every wire, pipe, or duct that passes through the fire separation needs to be sealed with approved fire-stop caulking or putty pads. This is one of the most common items that Ottawa building inspectors flag during framing and insulation inspections, so your contractor should be meticulous about it.

Doors between the garage and the house must be solid-core steel or solid-core wood with a minimum 20-minute fire rating. They also need to be self-closing, meaning they have a spring hinge or door closer that pulls them shut automatically. The door cannot open directly into a bedroom. Most designs route the garage entry through a mudroom, laundry room, or hallway instead.

The floor of the garage must be a concrete slab, and if the garage floor is lower than the adjacent house floor, you need a step up of at least 100 mm (about 4 inches) from the garage slab to the house floor. This prevents fuel vapours, which are heavier than air, from flowing into the living space.

Vapour and Gas Barriers

Beyond the fire-rated assembly itself, the code requires that the garage be sealed to prevent carbon monoxide and other vehicle exhaust gases from migrating into the house. This means all joints and penetrations in the shared wall need to be sealed airtight, not just fire-stopped. Many builders use a combination of acoustic sealant and fire caulking to achieve both requirements simultaneously.

During the permit process through City of Ottawa Building Code Services, your plans will be reviewed for compliance with these fire separation requirements. The inspector will check the assembly at the framing stage and again before drywall is finished. If anything is missed, they will require corrections before you can proceed, so it pays to get it right the first time.

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