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Code guide

Ontario Building Code Smoke and Carbon Monoxide Alarm Requirements

Smoke detector (smoke alarm) and CO alarm rules for new Ontario houses: every storey and bedroom, hard-wired, interconnected, with a strobe.
min strobe in sleeping rooms
175 cd
min strobe in sleeping rooms
smoke alarm battery backup, then 4 min alarm
7 days
smoke alarm battery backup, then 4 min alarm
CO alarm battery standby, then 12 h of alarm
8 h
CO alarm battery standby, then 12 h of alarm
max silence from a smoke alarm hush button
10 min
max silence from a smoke alarm hush button

Last updated

In a new Ontario house, the 2024 Building Code requires a smoke alarm on every storey including the basement, in every bedroom, and between the bedrooms and the rest of the storey (OBC Div. B 9.10.19.3.OBC Div. B 9.10.19.3. Location of Smoke Alarms(1) Except as permitted in Article 9.10.19.8., within dwelling units, sufficient smoke alarms shall be installed so that (a) there is at least one smoke alarm installed on each storey, including basements, and (b) on any storey of a dwelling unit containing sleeping rooms, a smoke alarm is installed (i) in each…), all hard-wired with battery backup and interconnected (9.10.19.4.OBC Div. B 9.10.19.4. Power Supply(1) Except as provided in Sentences (2) and (3), smoke alarms described in Sentence 9.10.19.1.(1) and 9.10.19.3.(1.1) shall (a) be installed with permanent connections to an electrical circuit, (See Note A-3.2.4.20.(9) (a)) (b) have no disconnect switch between the overcurrent device and the smoke alarm, and (c) in…, 9.10.19.5.OBC Div. B 9.10.19.5. Interconnection of Smoke Alarms(1) Where more than one smoke alarm is required in a dwelling unit, the smoke alarms shall be wired so that the activation of one alarm will cause all alarms within the dwelling unit to sound. (2) Smoke alarms in a house with a secondary suite shall be wirelessly interconnected or interconnected by hard-wiring so that…). Where the house has a fuel-burning appliance or an attached garage, carbon monoxide alarms are also required next to each sleeping area and on each storey without one (OBC Div. B 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…).

One requirement many people miss: required smoke alarms and CO alarms must include a visual signalling component (a strobe) meeting NFPA 72. This page covers the Building Code rules for new construction and renovation in Part 9 buildings. Alarms in existing homes are also governed by the Ontario Fire Code, which is a separate regulation. Your building department and local fire service have the final word.

Alarm requirements at a glance

Item Smoke alarms CO alarms
Where (house) each storey incl. basement; each bedroom; between bedrooms and the rest of the storey adjacent to each sleeping room; each storey without a sleeping room; inside bedrooms in some cases
Mounting on or near the ceiling manufacturer's height, otherwise on or near the ceiling
Power hard-wired, no disconnect switch hard-wired, no disconnect switch
Battery backup 7 days, then 4 min of alarm 8 h standby, then 12 h of alarm
Interconnection all alarms in the dwelling unit (whole house with a secondary suite) all alarms in the suite (whole house with a secondary suite)
Visual signal required, 175 cd minimum in sleeping rooms required, 175 cd minimum in sleeping areas
Articles 9.10.19.1. to 9.10.19.6. 9.32.3.9. to 9.32.3.9C.

This table is our own summary.

Smoke alarms: where they go

Smoke alarms meeting CAN/ULC-S531 are required in each dwelling unit, each sleeping room outside a dwelling unit, and the common spaces of a house with a secondary suite (9.10.19.1.OBC Div. B 9.10.19.1. Required Smoke Alarms(1) Except as permitted by Article 9.10.19.8., smoke alarms conforming to CAN/ULC-S531, "Standard for Smoke Alarms," shall be installed in (a) each dwelling unit, (b) each sleeping room not within a dwelling unit, and (c) ancillary spaces and common spaces not in dwelling units in a house with a secondary suite. (2)…). Within a dwelling unit (9.10.19.3.OBC Div. B 9.10.19.3. Location of Smoke Alarms(1) Except as permitted in Article 9.10.19.8., within dwelling units, sufficient smoke alarms shall be installed so that (a) there is at least one smoke alarm installed on each storey, including basements, and (b) on any storey of a dwelling unit containing sleeping rooms, a smoke alarm is installed (i) in each…):

  • at least one on each storey, including basements;
  • on any storey with sleeping rooms, one in each sleeping room and one between the sleeping rooms and the remainder of the storey, placed in the hallway if the bedrooms open off one;
  • in a house with a secondary suite that has an interior shared exit or common area, one in each of those spaces;
  • installed to CAN/ULC-S553, on or near the ceiling.

Power, interconnection and silencing

  • Power. Permanently connected to an electrical circuit, with no disconnect switch between the overcurrent device and the alarm, plus a battery that can run the alarm for at least 7 days and then sound for 4 minutes. Battery-only alarms are allowed only where the building has no electrical power (9.10.19.4.OBC Div. B 9.10.19.4. Power Supply(1) Except as provided in Sentences (2) and (3), smoke alarms described in Sentence 9.10.19.1.(1) and 9.10.19.3.(1.1) shall (a) be installed with permanent connections to an electrical circuit, (See Note A-3.2.4.20.(9) (a)) (b) have no disconnect switch between the overcurrent device and the smoke alarm, and (c) in…).
  • Interconnection. Where more than one alarm is required in a dwelling unit, one going off must set off all of them. In a house with a secondary suite, every alarm in the house must be interconnected, by hard-wiring or wirelessly (9.10.19.5.OBC Div. B 9.10.19.5. Interconnection of Smoke Alarms(1) Where more than one smoke alarm is required in a dwelling unit, the smoke alarms shall be wired so that the activation of one alarm will cause all alarms within the dwelling unit to sound. (2) Smoke alarms in a house with a secondary suite shall be wirelessly interconnected or interconnected by hard-wiring so that…).
  • Sound. The alarm must use the temporal pattern, or temporal pattern combined with voice (9.10.19.2.OBC Div. B 9.10.19.2. Sound Patterns of Smoke Alarms(1) The sound patterns of smoke alarms shall (a) meet the temporal patterns of alarm signals, or (See Note A-3.2.4.18.(2)) (b) be a combination of temporal pattern and voice relay.).
  • Silencing. A manual hush button may silence the alarm for not more than 10 minutes before it resets (9.10.19.6.OBC Div. B 9.10.19.6. Silencing of Smoke Alarms(1) Except as permitted in Sentence (2), a manually operated device shall be incorporated within the circuitry of a smoke alarm installed in a dwelling unit so that the signal emitted by the smoke alarm can be silenced for a period of not more than 10 min, after which the smoke alarm will reset and sound again if the…).

A residential fire warning system installed to CAN/ULC-S540 can replace the smoke alarms, if it meets the same sound, power and silencing rules (9.10.19.8.OBC Div. B 9.10.19.8. Residential Fire Warning Systems(1) Except where a fire alarm system is installed or required in a building, smoke detectors forming part of a residential fire warning system installed in conformance with CAN/ULC-S540 "Standard for Residential Fire and Life Safety Warning Systems: Installation, Inspection, Testing and Maintenance," are permitted to…).

The visual signal

Required smoke alarms must have a visual signalling component meeting the light, colour and pulse requirements in NFPA 72, with at least 175 cd where installed in sleeping rooms (9.10.19.1.(2) to (4)OBC Div. B 9.10.19.1. Required Smoke Alarms(1) Except as permitted by Article 9.10.19.8., smoke alarms conforming to CAN/ULC-S531, "Standard for Smoke Alarms," shall be installed in (a) each dwelling unit, (b) each sleeping room not within a dwelling unit, and (c) ancillary spaces and common spaces not in dwelling units in a house with a secondary suite. (2)…, 9.10.19.3.(4) to (6)OBC Div. B 9.10.19.3. Location of Smoke Alarms(1) Except as permitted in Article 9.10.19.8., within dwelling units, sufficient smoke alarms shall be installed so that (a) there is at least one smoke alarm installed on each storey, including basements, and (b) on any storey of a dwelling unit containing sleeping rooms, a smoke alarm is installed (i) in each…). In a house or a house with a secondary suite, that strobe need not be built into the alarm if it is interconnected with it, need not have battery backup, and need not flash in sync with others. CO alarms have a matching requirement (9.32.3.9C.(3) to (5)OBC Div. B 9.32.3.9C. Installation and Conformance to Standards(1) The carbon monoxide alarms required by Articles 9.32.3.9A. and 9.32.3.9B. shall (a) except as permitted in Sentence (2), be permanently connected to an electrical circuit and shall have no disconnect switch between the overcurrent device and the carbon monoxide alarm, (b) in case the regular power supply to the…).

Carbon monoxide alarms

When they apply. 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 that contain a fuel-burning appliance or a storage garage (read Clause (1)(a) for the exact conditions), and to residential buildings served by a forced-air fuel-burning appliance outside the building. A suite needs CO alarms where it has a fuel-burning appliance or flue, is heated directly by a forced-air fuel-burning appliance, or shares a wall, floor or ceiling with a room containing one, or with a storage garage (9.32.3.9A.(1)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…).

Where. In a residential suite, a CO alarm goes adjacent to each sleeping room and on each storey without a sleeping room. A bedroom that itself contains a fuel-burning appliance or flue, or shares a wall, floor or ceiling with a garage or a fuel-burning room outside the suite, needs its own CO alarm inside (9.32.3.9A.(2) to (4)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…). Service rooms outside suites with fuel-burning equipment also need one (9.32.3.9B.OBC Div. B 9.32.3.9B. Location of Carbon Monoxide Alarms in All Buildings(1) A carbon monoxide alarm shall be installed in service rooms or other areas of a building where the service room or other area (a) contains a fuel-burning appliance used for building services or laundry drying equipment, and (b) is not located within a suite of residential occupancy.).

How. Hard-wired with no disconnect switch, battery backup for 8 hours standby followed by 12 hours of alarm, interconnected within the suite (and across a house with a secondary suite), audible in bedrooms with doors closed, listed to CSA 6.19 or UL 2034, and mounted at the manufacturer's recommended height or on or near the ceiling (9.32.3.9C.OBC Div. B 9.32.3.9C. Installation and Conformance to Standards(1) The carbon monoxide alarms required by Articles 9.32.3.9A. and 9.32.3.9B. shall (a) except as permitted in Sentence (2), be permanently connected to an electrical circuit and shall have no disconnect switch between the overcurrent device and the carbon monoxide alarm, (b) in case the regular power supply to the…).

Common mistakes

  1. Only one alarm per floor on a bedroom storey. Each bedroom needs its own as well.
  2. Battery-only alarms in a new build or new suite.
  3. Separate, non-interconnected alarms in the two units of a house with a secondary suite.
  4. Forgetting the CO alarm inside a bedroom over or beside an attached garage.
  5. Skipping the strobe, which is easy to overlook when buying a standard alarm.

How to look it up yourself

In Division B, Part 9 of the 2024 Compendium, search for "Location of Smoke Alarms" (Subsection 9.10.19.) and "Location of Carbon Monoxide Alarms" (Article 9.32.3.9A.). Other useful phrases: "visual signalling component", "Interconnection of Smoke Alarms" and "Installation and Conformance to Standards". Note that CO alarms are in Section 9.32, "Ventilation", not in the fire protection section.

Alarm rules come up on both the House and Small Buildings exams. Read the free study guide for the House exam and try the free practice quiz on that 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

Is a smoke detector the same as a smoke alarm?
Not in the code. A smoke alarm is a single device that both detects smoke and sounds the alarm, which is what houses use. A smoke detector is a detection device that signals a separate fire alarm system, as in larger buildings (Division A, Article 1.4.1.2., definitions). Most people say smoke detector when they mean a smoke alarm.
Where are smoke alarms required in an Ontario house?
At least one on each storey including basements, and on each storey with bedrooms, one in each sleeping room plus one between the sleeping rooms and the rest of the storey (in the hallway if there is one). They go on or near the ceiling (Division B, Article 9.10.19.3.).
Do smoke alarms have to be hard-wired in Ontario?
For new construction, yes, where the building has electrical power: permanently connected to a circuit with no disconnect switch, plus a battery backup lasting at least 7 days followed by 4 minutes of alarm (Division B, Article 9.10.19.4.).
Do smoke alarms have to be interconnected?
Where more than one is required in a dwelling unit, they must be wired so one sounds them all. In a house with a secondary suite, all alarms in the house must be interconnected, by hard-wiring or wirelessly (Division B, Article 9.10.19.5.).
Do new smoke alarms need a strobe light?
The 2024 code requires required smoke alarms to have a visual signalling component meeting NFPA 72, at least 175 cd in sleeping rooms. In a house it need not be built into the alarm if interconnected, need not have battery backup and need not be synchronized (Division B, Articles 9.10.19.1. and 9.10.19.3.).
Where do carbon monoxide alarms go in a new house?
Where a suite has a fuel-burning appliance or an attached garage (among other triggers), a CO alarm is needed next to each sleeping room and on each storey without a sleeping room, and inside a bedroom that itself contains a fuel-burning appliance or shares a wall or floor with a garage (Division B, Articles 9.32.3.9. and 9.32.3.9A.).