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Code guide

Ontario Building Code Firewalls and Fire Separations for Houses

Firewalls, party walls, suite separations and attached garage walls for Ontario houses under the 2024 Building Code, with the ratings and articles.
residential party wall, no unit above another
1 h
residential party wall, no unit above another
between residential suites, generally
45 min
between residential suites, generally
Type X gypsum barrier, secondary suite house
15.9 mm
Type X gypsum barrier, secondary suite house

Last updated

Under the 2024 Ontario Building Code, a party wall on a property line must be a firewall, except that a residential party wall between two dwelling units with no unit above the other (typical semis and townhouses) may be a 1 h fire separation running from the footings to the underside of the roof deck (OBC Div. B 9.10.11.2.OBC Div. B 9.10.11.2. Firewalls Not Required(1) A party wall on a property line of a building of residential occupancy need not be constructed as a firewall, provided it is constructed as a fire separation having not less than a 1 h fire-resistance rating, where the party wall separates (a) two dwelling units where there is no dwelling unit above another…). Inside buildings, residential suites are generally separated by 45 min fire separations (OBC Div. B 9.10.9.16.OBC Div. B 9.10.9.16. Separation of Residential Suites(1) Except as provided in Sentences (2) and (3) and Article 9.10.21.2., suites in residential occupancies shall be separated from adjacent rooms and suites by a fire separation having a fire-resistance rating of not less than 45 min. (2) Sleeping rooms in boarding, lodging or rooming houses where sleeping…), while an attached garage serving only its own house needs no fire rating but does need a gas-tight barrier and a self-closing door (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…).

People search for "Ontario building code firewall" when they mean several different things: the wall between semis, the wall to an attached garage, or the ceiling over a basement apartment. This page sorts those out for Part 9 buildings. Your building department decides how the code applies to your project and may impose permit conditions.

Key ratings at a glance

Situation Requirement Article
Party wall on a property line (general) firewall 9.10.11.1.
Residential party wall, no dwelling unit above another 1 h fire separation, footings to roof deck 9.10.11.2.
Party wall between detached garages on adjacent properties 45 min fire separation 9.10.11.4.
Residential suite to adjacent rooms and suites 45 min 9.10.9.16.(1)
Dwelling unit of 2 or more storeys (incl. basement) to rest of building 1 h 9.10.9.16.(3)
House with a secondary suite, between units 15.9 mm Type X gypsum smoke-tight barrier (waived if sprinklered) 9.10.9.16.(4), (5)
Residential to other major occupancies 1 h (2 h to mercantile or medium hazard industrial) 9.10.9.13.
Attached garage serving only its dwelling unit no fire separation; air barrier and self-closing door 9.10.9.18.(3), (4)
Other storage garages (5 vehicles or fewer) 1 h 9.10.9.18.(2)

Our own summary. Each line has exceptions in the full article.

Firewall versus fire separation

The definitions in Division A explain the difference. A fire separation is a construction assembly that acts as a barrier against the spread of fire (Div. A 1.4.1.2.OBC Div. A 1.4.1.2.(1) Fire separationFire separation means a construction assembly that acts as a barrier against the spread of fire. (See Note A-1.4.1.2.(1))). A firewall is a particular kind of fire separation: noncombustible, rated as the code prescribes, and structurally able to stay standing for that rated time (Div. A 1.4.1.2.OBC Div. A 1.4.1.2.(1) FirewallFirewall means a type of fire separation of noncombustible construction that subdivides a building or separates adjoining buildings to resist the spread of fire and that has a fire-resistance rating as prescribed in this Code and has structural stability to remain intact under fire conditions for the required…). A fire-resistance rating is the time an assembly withstands flame and heat in a standard test (Div. A 1.4.1.2.OBC Div. A 1.4.1.2.(1) Fire-resistance ratingFire-resistance rating means the time in minutes or hours that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire under specified conditions of test and performance criteria, or as determined by extension or interpretation of information derived…).

Where firewalls are used in a Part 9 building, Part 3 governs their construction (9.10.11.3.OBC Div. B 9.10.11.3. Construction of Firewalls(1) Where firewalls are used, the requirements in Part 3 shall apply.).

Semis, townhouses and party walls

9.10.11.1.OBC Div. B 9.10.11.1. Required Firewalls(1) Except as provided in Articles 9.10.11.2., a party wall on a property line shall be constructed as a firewall. requires a party wall on a property line to be a firewall. 9.10.11.2.OBC Div. B 9.10.11.2. Firewalls Not Required(1) A party wall on a property line of a building of residential occupancy need not be constructed as a firewall, provided it is constructed as a fire separation having not less than a 1 h fire-resistance rating, where the party wall separates (a) two dwelling units where there is no dwelling unit above another… relaxes that for residential buildings: a party wall may instead be a fire separation of at least 1 h where it separates two dwelling units with no dwelling unit above another, a dwelling unit and a house with a secondary suite, or two houses with a secondary suite. The wall must give continuous protection from the top of the footings to the underside of the roof deck, and any space at the top must be tightly filled with mineral wool or noncombustible material.

Where detached garages on neighbouring lots are built against each other, the shared wall needs a 45 min fire separation (9.10.11.4.OBC Div. B 9.10.11.4. Firewalls in Detached Garages(1) Where a garage is detached from the dwelling unit it serves but attached to another garage on the adjacent property, the party wall so formed shall be constructed as a fire separation having a fire-resistance rating of not less than 45 min.).

Separations inside the building

  • Suites. Residential suites are separated from adjacent rooms and suites by at least 45 min. A dwelling unit with 2 or more storeys, counting a basement, is separated from the rest of the building by at least 1 h (9.10.9.16.OBC Div. B 9.10.9.16. Separation of Residential Suites(1) Except as provided in Sentences (2) and (3) and Article 9.10.21.2., suites in residential occupancies shall be separated from adjacent rooms and suites by a fire separation having a fire-resistance rating of not less than 45 min. (2) Sleeping rooms in boarding, lodging or rooming houses where sleeping…).
  • Houses with a secondary suite. Instead of rated assemblies, walls and floor framing between the units (and their common spaces) may be protected by a continuous smoke-tight barrier of at least 15.9 mm Type X gypsum board on both sides of walls and the underside of floor framing. The rating is waived if the house is sprinklered (9.10.9.16.(4) and (5)OBC Div. B 9.10.9.16. Separation of Residential Suites(1) Except as provided in Sentences (2) and (3) and Article 9.10.21.2., suites in residential occupancies shall be separated from adjacent rooms and suites by a fire separation having a fire-resistance rating of not less than 45 min. (2) Sleeping rooms in boarding, lodging or rooming houses where sleeping…). See secondary suites.
  • Mixed occupancies. Residential occupancies are separated from other major occupancies by 1 h, or 2 h from mercantile and medium hazard industrial uses, with a 1 h allowance where not more than two dwelling units share a building with a store (9.10.9.13.OBC Div. B 9.10.9.13. Separation of Residential Occupancies(1) Except as provided in Sentences (2) and (4), residential occupancies shall be separated from all other major occupancies by a fire separation having a fire-resistance rating of not less than 1 h. (2) Except as provided in Sentence (3), a major occupancy classified as a residential occupancy, including live/work…).
  • Furnace rooms. Fuel-fired appliances generally go in a service room with a 1 h separation, but space-heating, space-cooling and water-heating appliances serving one room or suite, or a building of not more than 400 m² and 2 storeys, are generally exempt (9.10.10.4.OBC Div. B 9.10.10.4. Locations of Fuel-Fired Appliances(1) Except as provided in Sentences (2) and (3) and Article 9.10.10.5., fuel-fired appliances shall be located in a service room separated from the remainder of the building by a fire separation having not less than a 1 h fire-resistance rating. (2) Except as required in the appliance installation standards referenced…).

Attached garages

A storage garage is normally separated from other occupancies by 1.5 h, or 1 h for 5 vehicles or fewer. A garage serving only the dwelling unit it is attached to or built into counts as part of that dwelling unit, so no fire separation is needed between them (9.10.9.18.(1) to (3)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…). What is required instead:

  • an air barrier system conforming to Subsection 9.25.3. between the garage and the house, to keep out 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…), with sealed and supported joints where membranes are used;
  • a door that is tight-fitting, weather-stripped and fitted with a self-closing device (9.10.13.15.(1)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…);
  • no doorway into a bedroom (9.10.13.15.(2)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…).

Keeping the separation continuous

A rated wall only works if it stays continuous. Fire separations must be continuous barriers, with firestops at joints where they meet other separations, floors, ceilings and roofs (9.10.9.2.OBC Div. B 9.10.9.2. Continuous Barrier(1) Except as permitted in Article 9.10.9.3., a wall or floor assembly required to be a fire separation shall be constructed as a continuous barrier against the spread of fire and retard the passage of smoke. (2) Except as permitted in Article 9.10.9.3., a wall or floor assembly required to be a smoke-tight barrier…). Penetrations by pipes, wires and ducts must be firestopped or tightly fitted as set out in 9.10.9.6.OBC Div. B 9.10.9.6. General Requirements for Penetrations of Fire Separations(1) Except as required by Sentence (2) and Articles 9.10.9.7. and 9.10.9.8. and as permitted by Article 9.10.9.9., penetrations of a required fire separation or a membrane forming part of an assembly required to be a fire separation shall be (a) sealed by a firestop that, when subjected to the fire test method in…. Doors in fire separations need self-closing devices (9.10.13.10.OBC Div. B 9.10.13.10. Self-Closing Device(1) Except as described in Sentence (2), every door in a fire separation shall have a self-closing device. (2) Self-closing devices are not required between public corridors and suites in business and personal services occupancies, except in dead-end corridors or a corridor that serves a hotel.).

Common mistakes

  1. Stopping a party wall at the ceiling instead of carrying it to the underside of the roof deck.
  2. Leaving the top gap open or stuffing it with ordinary batt insulation rather than mineral wool or noncombustible material.
  3. Removing the garage door closer or weather-stripping during a renovation.
  4. Unsealed penetrations through the garage air barrier or a suite separation.
  5. Treating "firewall" and "fire separation" as the same thing on drawings or in an exam answer.

How to look it up yourself

In Division B, Part 9 of the 2024 Compendium, Section 9.10 is "Fire Protection". Search for:

  • "Firewalls Not Required"
  • "Separation of Residential Suites"
  • "Separation of Storage Garages"
  • "Doors Between Garages and Dwelling Units"
  • "smoke-tight barrier"

For definitions, search Division A for "Firewall means".

Fire separations are tested on both the House and Small Buildings exams. Use the free study guide for the Small Buildings exam or House exam, and try the free practice quiz on each 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 a semi-detached or townhouse party wall need to be a firewall in Ontario?
A party wall on a property line must normally be a firewall, but a residential party wall separating two dwelling units, where no dwelling unit is above another, can instead be a fire separation with at least a 1 h fire-resistance rating. It must run continuously from the top of the footings to the underside of the roof deck, with any gap at the top tightly filled with mineral wool or noncombustible material (Division B, Articles 9.10.11.1. and 9.10.11.2.).
What is the difference between a firewall and a fire separation?
A fire separation is any assembly that acts as a barrier against the spread of fire. A firewall is a special type of fire separation: noncombustible, with a prescribed fire-resistance rating, and structurally stable enough to stay standing for that rated time (Division A, 1.4.1.2. definitions).
Does the wall between a house and its attached garage need a fire rating?
Not when the garage serves only the dwelling unit it is attached to; it is treated as part of that dwelling unit. But there must be an air barrier system against gas and exhaust fumes, and the door must be tight-fitting, weather-stripped and self-closing (Division B, Article 9.10.9.18. and 9.10.13.15.).
Can the door from the garage open into a bedroom?
No. A doorway between an attached or built-in garage and a dwelling unit must not be located in a room intended for sleeping (Division B, Sentence 9.10.13.15.(2)).
What fire rating is needed between apartments or suites?
Residential suites must generally be separated from adjacent rooms and suites by a fire separation of at least 45 min, and dwelling units of 2 or more storeys including basements by at least 1 h (Division B, Article 9.10.9.16.). Houses with a secondary suite have their own rules.