Attached Garage Gas-Proofing Rules in Canada (NBC)

In Canada an attached garage has to be sealed against fumes, not fire-rated. Part 9 of the National Building Code (NBC 2020) asks for an air barrier between the garage and the rest of the house that stops gas and exhaust, and for a tight-fitting, weatherstripped, self-closing door between them, which may not open into a room used for sleeping. For a garage that serves only the house it is attached to, the code waives the 1 h fire separation it otherwise requires around a storage garage.

What the code asks for

Two articles in Part 9 of the NBC 2020 do the work: 9.10.9.18 (separation of storage garages, which covers a garage attached to a house) and 9.10.13.15 (the door). The code’s explanatory note, as published in British Columbia’s version, says the gas-tight barrier is there to keep carbon monoxide and gasoline fumes out of the dwelling, and that all joints must be sealed. The garage article was numbered 9.10.9.16 in earlier editions and in Ontario’s 2012 code (and in BC’s 2018 code), so older guides and handouts quote that number; Alberta’s 2023 edition of the NBC uses 9.10.9.18. Which number appears in the 2024 Ontario code we could not confirm, so check the clause in the edition your permit is under.

The air barrier is the part people miss. A finished garage wall is not automatically a gas-tight one. The air barrier system has to meet the NBC’s air barrier subsection (9.25.3) and be installed between the garage and the rest of the house; where membrane materials provide the airtightness, the code says all joints must be sealed and structurally supported. Continuity is the point, so plan how the barrier passes the wall-to-ceiling corner and any pipe, wire or duct that goes through it, and ask your building department how it wants that shown.

The door between the garage and the house

• Tight-fitting and weatherstripped, so exhaust cannot slip past the edges.
• Self-closing, with a spring hinge or a closer. A door that stays propped open defeats the whole assembly.
• Never into a bedroom. The code says a doorway between the garage and a dwelling unit may not be in a room intended for sleeping.

Notice what is missing: article 9.10.13.15 does not name a door material or a fire rating. Municipalities or provincial amendments can add their own requirements, so ask your building department before you order a door.

Why there is usually no fire rating

The NBC normally requires a fire separation around a storage garage, 1 h for a garage of five vehicles or fewer and 1.5 h for a larger one. That requirement is waived where the garage serves only the dwelling unit it is attached to or built into, because the garage is then treated as part of that unit. A garage shared by several units, or one under an apartment building, does not get that relief and has to meet the fire-separation rules for storage garages. Provinces word the waiver differently: Ontario’s 2017 amendment refers to the house or the individual dwelling unit, and Alberta has issued an interpretation (23-BCI-035) for a house with a secondary suite. If you have a suite, ask your building department how the waiver applies.

Ontario, British Columbia and Alberta each adopt the NBC with their own changes (Ontario Building Code 2024, BC Building Code 2024, Alberta’s NBC(AE) 2023). The OBC carries equivalent articles, and the gas-tight door and no-bedroom-door rules read much the same across them, but wording and numbering are not identical. Treat the table above as the national baseline and confirm the provincial text.

How this differs from the US IRC

The US rules are a fire-and-fumes package, with prescribed board thicknesses and door types; the Canadian rules are about air-tightness. A house built to one will often be close to the other, but a US garage with 13 mm drywall taped and sealed is not automatically a gas-tight Canadian one, and a Canadian garage with a sealed air barrier and a hollow-core door would fail the US door rule. Our garage fire separation guide walks through the IRC side in detail.

The separation on a ranch plan

FloorGen’s 3-bed ranch with 2-car garage has a garage drawn 6.71 × 7.32 m (22 × 24 ft) on its wall grid, 47.1 m² (507 ft²) net inside the walls, at the west end of a single-storey house. The garage shares walls with the entry, the kitchen, the dining room and the laundry / mudroom, and the only door into the house goes to the laundry / mudroom, 10.2 m² (110 ft²) net. No bedroom touches the garage, so the no-bedroom-door rule is met by the layout, not by a detail. Sizes written on the 2D image run along wall centrelines; areas are net to the inner wall faces.

Putting the garage door at a mudroom rather than the kitchen is practical for gas-proofing too: a self-closing door is less of a nuisance when it opens onto a space people pass through carrying boots and bags. For a common two-car garage size and how it sits on a lot, see our garage size guide.

A bonus room over the garage

The ranch is one storey, so there is no room above its garage, but many Canadian homes put one there. The floor of that room is now part of the separation: it needs the same sealed air barrier on the garage side as a wall would, and any duct or stair opening between the two has to respect it. The usual comfort issues, roof pitch and headroom are covered in our bonus room over a garage guide, and fire rules for a room above vary by province, so ask your building department what applies before you frame it.

FloorGen does not check fire separation, air barriers or door types, so draw the plan, then mark the separation walls and the garage door on it for your permit set. Related Canadian reading: metric vs imperial floor plans in Canada.