Secondary Suites and the Ontario Building Code

What counts as a secondary suite

A secondary suite is a self-contained dwelling unit in a building of only residential occupancy that has just one other dwelling unit plus common spaces, with both units forming a single real estate entity (Div. A 1.4.1.2.OBC Div. A 1.4.1.2.(1) Secondary suiteSecondary suite means a self-contained dwelling units located in a building or portion of a building of only residential occupancy that contains only one other dwelling units and common spaces, and where both dwelling units constitute a single real estate entity. (See Note A-1.4.1.2.(1))). In other words, a house with two units under one ownership. A building with three units, or two units that are sold separately, is treated differently.

Fire and smoke protection

The barrier between units. The normal rule for residential suites is a 45 min fire separation, or 1 h for a dwelling unit of two or more storeys. For a house with a secondary suite, walls and floor framing separating the units from each other and from common spaces may instead be protected by a continuous smoke-tight barrier of at least 15.9 mm thick 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…). The barrier must be continuous, with joints and penetrations sealed (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…).

Floors and supports. Floors within a house with a secondary suite need not be fire separations (9.10.9.4.OBC Div. B 9.10.9.4. Floor Assemblies(1) Except as permitted in Sentences (2) to (4), all floor assemblies shall be constructed as fire separations. (2) Floor assemblies contained within dwelling units and within houses with a secondary suite need not be constructed as fire separations. (3) Floor assemblies for which no fire-resistance rating is required…), and the floor fire-resistance table does not apply where the floor framing has the Type X barrier on its underside (9.10.8.10.OBC Div. B 9.10.8.10. Non-Application to Houses(1) Table 9.10.8.1. does not apply to (a) a dwelling unit that has no other dwelling unit above or below it, (b) houses with a secondary suite, where the floor framing is protected on the underside by a continuous smoke-tight barrier of not less than 15.9 mm thick Type X gypsum board, or (c) a dwelling unit that is…). Walls, columns and beams that support the floor between the units must be protected by 15.9 mm Type X gypsum board (9.10.8.3.(2)OBC Div. B 9.10.8.3. Fire-Resistance Ratings for Walls, Columns and Arches(1) Except as otherwise provided in this Subsection, all loadbearing walls, columns and arches in the storey immediately below a floor or roof assembly shall have a fire-resistance rating of not less than that required for the supported floor or roof assembly. (2) Light-frame walls, columns, arches and beams as well…).

Furnace room. A shared furnace or water heater may sit in a service room whose walls (both sides) and ceiling are lined with a continuous smoke-tight barrier of 15.9 mm Type X gypsum board, instead of a 1 h service room (9.10.10.4.(2)(b)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…).

Ducts. An air duct system serving one of the units must not be directly interconnected with other parts of the house (9.33.1.1.(3)OBC Div. B 9.33.1.1. Application(1) This Section applies to the design and installation of (a) heating systems, including requirements for combustion air, and air-conditioning systems serving only one dwelling unit, and (b) radiant heating systems in houses with a secondary suite including their common spaces. (2) The design and installation of…), which stops smoke travelling between units through shared ductwork.

Alarms. Smoke alarms are required in each unit and in common spaces, and every alarm in the house must be interconnected, by wire or wirelessly (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)…, 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 CO alarms are required, they are interconnected across the house too (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…). See smoke and CO alarms.

Heights, egress and stairs

• Ceiling height. At least 1.95 m in the suite, and 1.85 m clear under beams and ducting (9.5.3.1.OBC Div. B 9.5.3.1. Ceiling Heights of Rooms or Spaces(1) Except as provided in Sentences (2) and (3), the ceiling heights and clear heights in rooms or spaces in residential occupancies and live/work units shall conform to Table 9.5.3.1. (2) Ceiling heights in secondary suites shall be not less than 1.95 m. (3) Clear heights under beams and ducting in secondary suites…). See ceiling heights and room sizes.
• Stairs. Stairs in a house with a secondary suite follow the private stair rules, with 1,950 mm headroom generally and 1,850 mm under beams and ducting in the suite (9.8.2.2.OBC Div. B 9.8.2.2. Height Over Stairs(1) The clear height over stairs shall be measured vertically, over the clear width of the stair, from a straight line tangent to the tread and landing nosings to the lowest point above. (See Note A-3.4.3.4.) (2) Except as provided in Sentences (3) and (4) and Article 9.8.4.7., the clear height over stairs shall not…).
• Bedroom windows. Each floor level with a bedroom needs an egress window or a door directly outside (9.9.10.1.OBC Div. B 9.9.10.1. Egress Windows or Doors for Bedrooms(1) Except where a door on the same floor level as the bedroom provides direct access to the exterior, every floor level containing a bedroom in a suite shall be provided with at least one outside window that (a) is openable from the inside without the use of tools, (b) provides an individual, unobstructed open…).
• Upper unit egress. Where the upper unit's door opens onto an exterior passageway more than 1.5 m above ground, served by a single stair and with a floor rated under 45 min, the upper unit needs a second, separate means of egress (9.9.9.3.(2)OBC Div. B 9.9.9.3. Shared Egress Facilities(1) Except for dwelling units in a house with a secondary suite, a dwelling unit shall be provided with a second and separate means of egress where an egress door from the dwelling unit opens onto (a) an exit stairway serving more than one suite, (b) a public corridor (i) serving more than one suite, and (ii) served…).

Adding a suite to an existing house

Most suites go into houses that already exist. Part 11 applies to buildings that have been in existence for at least five years (Div. A 1.3.3.3B.OBC Div. A 1.3.3.3B. Application of Part 11(1) Except as provided in Sentence (2), Part 11 of Division B applies to the design and construction of existing buildings, or parts of existing buildings, that have been in existence for at least five years. (2) If a building has been in existence for at least five years but includes an addition that has been in…), and its compliance alternatives may be substituted for Part 9 requirements without proving that compliance is impracticable (11.5.1.1.(2)OBC Div. B 11.5.1.1. Compliance Alternatives(1) A compliance alternative shown in Table 11.5.1.1.-A, 11.5.1.1.-B, 11.5.1.1.-C, 11.5.1.1.-D/E or 11.5.1.1.-F may be substituted for a requirement contained in Part 3, 4, 6 or 8 where the chief building official is satisfied that compliance with the requirement is impracticable because, (a) of structural or…). For a house with a secondary suite, Table 11.5.1.1.-C includes, for example, a 15 min horizontal fire separation where smoke alarms are installed in every unit and common area and interconnected, a waived rating where the house is sprinklered, and alternatives for sound separation (Table 11.5.1.1.-COBC Div. B Table 11.5.1.1-C. Compliance Alternatives for Residential Occupancies — Forming Part of Article 11.5.1.1.Table 11.5.1.1.-C Compliance Alternatives for Residential Occupancies — Forming Part of Article 11.5.1.1. C.A. Number | Division B Requirements | Compliance Alternative C1 | 3.1.4.7. | Existing heavy timber construction acceptable where construction is within 90% of member sizes listed in Part 3. C2 | 3.1.5.2. to…). Your building department decides which alternatives fit your house.

How to look it up yourself

In the 2024 Compendium, search Division B for "house with a secondary suite". It appears in dozens of articles; the key ones are under "Separation of Residential Suites", "Ceiling Heights of Rooms or Spaces" and "Interconnection of Smoke Alarms". Search "smoke-tight barrier" for the Type X provisions, and search Part 11 for "Compliance Alternatives" for existing houses.

Secondary suite provisions run through Sections 9.5 to 9.10, all on the House exam syllabus. Read the free House exam study guide and take the free practice quiz on that page.