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Secondary suites and Code

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Secondary suites add a little extra complexity to a build, as there are some added layers of Building Code to navigate.

The intent is to ensure that the occupant(s) of both the main dwelling and the secondary suite are protected from the potential impact of fire in the other portion of the dwelling, and isolated from noise as well.

Here are some of the things to consider when planning a secondary suite.


A secondary suite can be no more than

  • 80 m2 (861 square feet), and
  • no more than 80 per cent of the total area of the house (excluding garage space), whichever is less.

If the suite planned is greater than this, then the structure will be treated as duplex instead.


  • Ceiling heights can be no less than 1.95 m (6’ 4-3/4”)
  • Heights under ducts and beams must be no less than 1.85 m (6’ 5/8”)
  • Stairs of secondary suite entrance/exit: 86 cm (2’ 9-5/8”)


Sound-deadening material (insulation) must be installed such as to isolate the secondary suite and the rest of the structure.

Fire safety:

Any exits in a house with a secondary suite shall be protected with 1/2 drywall (regular) on both sides, finished to prevent the passage/ingress of smoke into that area. []

The secondary suite and the main dwelling are treated somewhat as separate fire compartments, albeit not to the same degree as with a duplex or a multi-unit dwelling. To that end, there are some restrictions on how close doors/windows of different suites can be located from each other. [,,]

Loadbearing elements, including beams and posts may need to be protected with 1/2 drywall (regular) in situations where the dwelling unit is above the secondary suite []

The walls/ceilings between the main dwelling and secondary suite must be finished to be a smoke-tight barrier. [,] This can usually be achieved through the process of drywall and mud.

Smoke alarms must be interconnected throughout the structure: the same applies to carbon monoxide alarms, if required.

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