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Code guide

Ontario Building Code Attached Garage Rules

Attached garage rules in the 2024 Ontario Building Code: no fire rating for a private garage, but a gas-tight air barrier, self-closing door and CO alarms.
fire rating for a garage serving only its own house
None
fire rating for a garage serving only its own house
garage for 5 vehicles or fewer serving others
1 h
garage for 5 vehicles or fewer serving others
enclosed perimeter that turns a carport into a garage
60%
enclosed perimeter that turns a carport into a garage
detached garage size for the simpler foundation rules
55 m²
detached garage size for the simpler foundation rules

Last updated

Under the 2024 Ontario Building Code, an attached garage that serves only its own house is treated as part of that dwelling unit, so no fire-rated wall is needed between them (OBC Div. B 9.10.9.18.OBC Div. B 9.10.9.18. Separation of Storage Garages(1) Except as provided in Sentences (2) and (3), a storage garage shall be separated from other occupancies by a fire separation having not less than a 1.5 h fire-resistance rating. (2) Except as permitted in Sentence (3), storage garages containing 5 motor vehicles or fewer shall be separated from other occupancies…). Instead, the code requires a continuous air barrier against gas and exhaust fumes and a tight-fitting, weather-stripped, self-closing door that does not open into a bedroom (OBC Div. B 9.10.13.15.OBC Div. B 9.10.13.15. Doors Between Garages and Dwelling Units(1) A door between an attached or built-in garage and a dwelling unit shall be tight-fitting and weather-stripped to provide an effective barrier against the passage of gases and exhaust fumes and shall be fitted with a self-closing device. (2) A doorway between an attached or built-in garage and a dwelling unit shall…).

This page covers garages and carports of houses under Part 9 of Division B. Your building department has the final say, and zoning bylaws control size, setbacks and driveways. For walls between semis, townhouses and secondary suites, see firewalls and fire separations.

Attached garage rules at a glance

Item Rule in short Where to look
Garage serving only its own dwelling unit part of the dwelling unit, no fire separation 9.10.9.18.(3)
Garage for 5 vehicles or fewer serving others 1 h fire separation 9.10.9.18.(2)
Larger storage garages 1.5 h fire separation 9.10.9.18.(1)
Wall and ceiling between garage and house air barrier system to Subsection 9.25.3. 9.10.9.18.(4)(a)
Membrane air barriers joints sealed and structurally supported 9.10.9.18.(5)
Door to the house tight-fitting, weather-stripped, self-closing 9.10.13.15.(1)
Door location not in a room intended for sleeping 9.10.13.15.(2)
CO alarms required where the garage shares a wall, floor or ceiling with the suite 9.32.3.9A.
Floor sloped to drain liquids to the outdoors 9.35.2.2.
Foundations of unheated attached garages below frost level, unless Section 9.12 allows otherwise 9.35.3.2.(3)
Carport vs garage more than 60% of perimeter enclosed means garage 9.35.2.1.

This table is our summary of the articles, not a copy of the code.

Why there is no fire rating, and what replaces it

9.10.9.18.OBC Div. B 9.10.9.18. Separation of Storage Garages(1) Except as provided in Sentences (2) and (3), a storage garage shall be separated from other occupancies by a fire separation having not less than a 1.5 h fire-resistance rating. (2) Except as permitted in Sentence (3), storage garages containing 5 motor vehicles or fewer shall be separated from other occupancies… starts with a 1.5 h separation for storage garages, drops it to 1 h for garages holding 5 vehicles or fewer, and then removes it entirely where the garage serves only the dwelling unit it is attached to or built into. That is the normal case for a detached, semi or townhouse with its own garage.

The real hazard from a private garage is carbon monoxide and fuel vapour, so the code targets gas tightness instead of fire resistance:

  • An air barrier system meeting Subsection 9.25.3. must separate the garage from the rest of the building to stop gas and exhaust fumes (9.10.9.18.(4)OBC Div. B 9.10.9.18. Separation of Storage Garages(1) Except as provided in Sentences (2) and (3), a storage garage shall be separated from other occupancies by a fire separation having not less than a 1.5 h fire-resistance rating. (2) Except as permitted in Sentence (3), storage garages containing 5 motor vehicles or fewer shall be separated from other occupancies…). The general air barrier article, 9.25.3.1.OBC Div. B 9.25.3.1. Required Barrier to Air Leakage(1) Wall, ceiling and floor assemblies that separate conditioned space from unconditioned space or from the ground shall be constructed so as to include an air barrier system that will provide a continuous barrier to air leakage (a) from the interior of the building into wall, floor, attic or roof spaces sufficient to…, asks for a continuous barrier. In practice that means sealing the shared wall and the ceiling under any room above the garage, including penetrations by pipes, wires and ducts.
  • Membranes used as the air barrier need every joint sealed and structurally supported (9.10.9.18.(5)OBC Div. B 9.10.9.18. Separation of Storage Garages(1) Except as provided in Sentences (2) and (3), a storage garage shall be separated from other occupancies by a fire separation having not less than a 1.5 h fire-resistance rating. (2) Except as permitted in Sentence (3), storage garages containing 5 motor vehicles or fewer shall be separated from other occupancies…).

The fire rating does come back when the garage is shared. A garage serving a house and a secondary suite, or a row of townhouse units, is no longer "only the dwelling unit to which it is attached," so read Sentences (1) and (2) carefully.

The door between the garage and the house

9.10.13.15.OBC Div. B 9.10.13.15. Doors Between Garages and Dwelling Units(1) A door between an attached or built-in garage and a dwelling unit shall be tight-fitting and weather-stripped to provide an effective barrier against the passage of gases and exhaust fumes and shall be fitted with a self-closing device. (2) A doorway between an attached or built-in garage and a dwelling unit shall… sets two rules for every door between an attached or built-in garage and a dwelling unit:

  1. Gas-tight and self-closing. The door must be tight-fitting and weather-stripped to block gases and exhaust fumes, and it must have a self-closing device. A spring hinge or closer that actually latches the door meets the intent. A door held open with a wedge does not.
  2. Not into a bedroom. The doorway cannot be in a room intended for sleeping.

The code does not set a fire-protection rating for this door when the garage serves only the house, and it does not require a step down from the house to the garage. Builders often add a step anyway because of grade and the sloped slab.

Carbon monoxide alarms

An attached garage triggers CO alarms. 9.32.3.9.OBC Div. B 9.32.3.9. Application of Carbon Monoxide Alarms(1) Article 9.32.3.9A. applies to every building that (a) contains a supply duct, and contains a fuel-burning appliance or a storage garage, or (b) contains a residential occupancy and is served by a forced-air fuel-burning appliance not contained within the building. (2) Articles 9.32.3.9B. and 9.32.3.9C. apply to… applies the location rules to buildings with a storage garage (read Clause (1)(a) for the exact conditions), and 9.32.3.9A.OBC Div. B 9.32.3.9A. Location of Carbon Monoxide Alarms(1) A carbon monoxide alarm shall be installed in a suite of supply duct where (a) a fuel-burning appliance or a flue is installed in the suite, (b) a forced-air fuel-burning appliance provides heated air directly to the suite, (c) a fuel-burning appliance or a flue is located in a room, suite or area that shares a… requires CO alarms in a suite that shares a wall, floor or ceiling with a storage garage:

  • adjacent to each sleeping room, and on each storey without a sleeping room;
  • inside any bedroom that shares a wall, floor or ceiling with the garage, or that is next to an attic or crawl space the garage is also next to. A bedroom over the garage is the classic case.

See smoke and CO alarm requirements for installation and interconnection.

Floor, foundations and structure

Section 9.35 applies to garages and carports serving not more than one dwelling unit (9.35.1.1.OBC Div. B 9.35.1.1. Application(1) This Section applies to garages and carports serving not more than one dwelling unit.), and otherwise sends you to the normal Part 9 rules (9.35.1.2.OBC Div. B 9.35.1.2. Construction Requirements(1) The construction of a garage or carport shall conform to the requirements for other buildings in this Part except as provided in this Section.).

  • Floor slope. An attached or built-in garage floor must slope to drain liquids outdoors (9.35.2.2.OBC Div. B 9.35.2.2. Garage Floor(1) Where an attached or built-in garage is provided, the garage floor shall be sloped to drain liquids to the outdoors.).
  • Foundations. Garages need foundations under Sections 9.12 and 9.15, including under the garage door (9.35.3.1.OBC Div. B 9.35.3.1. Foundation Required(1) Except as permitted in this Subsection, foundations conforming to Sections 9.12. and 9.15. shall be provided for the support of carport and garage super-structures, including that portion beneath garage doors. (2) Detached garages of less than 55 m² floor area and not more than 1 storey in height that are not of…). Foundations for attached unheated garages go below frost level, except as Section 9.12 allows. In clay soils that move with moisture, an attached garage's foundation should be about as deep as the house's, and a slab-on-ground garage needs a construction joint where it meets the house slab (9.35.3.2.OBC Div. B 9.35.3.2. Protection from Damage Due to Soil Movement(1) In clay-type soils subject to significant movement with a change in soil moisture content, the foundation depth of carports or garages connected to a dwelling unit directly or by a breezeway shall be approximately the same depth as the foundation of the main building. (2) Where slab-on-ground construction is used…). See footings.
  • Small detached garages. A detached garage under 55 m², 1 storey, not masonry or masonry veneer, can sit on wood mud sills or a slab at least 100 mm thick (9.35.3.1.(2)OBC Div. B 9.35.3.1. Foundation Required(1) Except as permitted in this Subsection, foundations conforming to Sections 9.12. and 9.15. shall be provided for the support of carport and garage super-structures, including that portion beneath garage doors. (2) Detached garages of less than 55 m² floor area and not more than 1 storey in height that are not of…).
  • Finish and anchorage. Interior finish need not be applied to garage walls (9.35.4.1.OBC Div. B 9.35.4.1. Interior Finish(1) Interior finish need not be applied to garage and carport walls.), but walls and columns must be anchored against wind uplift (9.35.4.3.OBC Div. B 9.35.4.3. Anchorage(1) Garage or carport walls and columns shall be anchored to the foundation to resist wind uplift in conformance with Subsection 9.23.6., except that where a garage is supported on the surface of the ground, ground anchors shall be provided to resist wind uplift.).
  • Carport or garage? A roofed parking enclosure with more than 60% of its perimeter enclosed by walls, doors or windows is a garage (9.35.2.1.OBC Div. B 9.35.2.1. Carport Considered to be Garage(1) Where a roofed enclosure used for the storage or parking of motor vehicles has more than 60 percent of the total perimeter enclosed by walls, doors or windows, the enclosure shall be considered a garage.).

Common mistakes

  1. Unsealed penetrations in the shared wall or the garage ceiling.
  2. Removing the door closer or weather-stripping during a renovation.
  3. A garage door into a bedroom, or into a room later converted to one.
  4. Missing the CO alarm inside a bedroom over the garage.
  5. Assuming a shared garage needs no rating. Once it serves more than its own dwelling unit, Sentences (1) and (2) apply.
  6. A flat or back-sloped garage slab that drains toward the house.

How to look it up yourself

In Division B, Part 9 of the 2024 Compendium, search for these phrases from the code text:

  • "Separation of Storage Garages" (9.10.9.18.)
  • "Doors Between Garages and Dwelling Units" (9.10.13.15.)
  • "gas and exhaust fumes"
  • "storage garage shares a common wall" (the CO alarm trigger)
  • "Garages and Carports" (Section 9.35)

You can also open 9.10.9.18. in the code viewer and 9.35.2.2..

BCIN exam angle

Garage separation, the garage door and CO alarm triggers are common House and Small Buildings questions, usually testing the "serves only the dwelling unit" exception. Read the free House chapter on fire protection, smoke alarms and sound and the House chapter on plumbing, electrical, garages and special buildings, or the Small Buildings chapter on fire protection and sound transmission. Then try the free quiz on the House exam or Small Buildings exam page.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

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Frequently asked questions

Does an attached garage need a fire-rated wall in Ontario?
Not when the garage serves only the dwelling unit it is attached to or built into. The code treats it as part of that dwelling unit, so no fire separation is needed. A garage serving other units needs a fire separation of at least 1 h for 5 vehicles or fewer, and 1.5 h otherwise (Division B, Article 9.10.9.18.).
What are the rules for the door between the garage and the house?
It must be tight-fitting and weather-stripped to keep out gases and exhaust fumes, and it must have a self-closing device (Division B, Sentence 9.10.13.15.(1)).
Can a garage door open into a bedroom?
No. A doorway between an attached or built-in garage and a dwelling unit must not be in a room intended for sleeping (Division B, Sentence 9.10.13.15.(2)).
Does a house with an attached garage need a carbon monoxide alarm?
Yes, where the garage shares a wall, floor or ceiling with the suite. CO alarms go next to each sleeping room and on each storey without one, and inside any bedroom that shares a wall, floor or ceiling with the garage (Division B, Articles 9.32.3.9. and 9.32.3.9A.).
Does the garage floor have to slope?
Yes. The floor of an attached or built-in garage must slope to drain liquids to the outdoors (Division B, Article 9.35.2.2.).
Is drywall required inside an attached garage?
Section 9.35 says interior finish need not be applied to garage walls (Division B, Article 9.35.4.1.). The air barrier between the garage and the house is still required, and many builders use sealed gypsum board as part of it. Check what your building department accepts.