What fire separation is required between an in-law suite and main house in Ontario?

When you add an in-law suite to your home, the Ontario Building Code treats it as a second dwelling unit, and the wall, floor or ceiling between the two units has to be built as a fire separation. Getting it right matters for permit approval and, more importantly, for the safety of everyone in both units.

The City of Ottawa always requires a building permit for a secondary unit in a house, and the permit drawings must show the fire-separation wall and floor-ceiling construction. For new construction, the Building Code calls for a 45-minute fire separation, or 15.9 mm (5/8 in) Type X gypsum on both sides of separating walls and on the underside of floor-ceiling framing. An addition is new construction, so expect your designer to work from those requirements.

If the unit is being created in part of an existing house rather than a new addition, Part 11 compliance alternatives can allow a 15-minute separation when interconnected smoke alarms are installed. Your designer confirms which path applies and the exact assembly for your framing.

Doors and openings in the separation are where problems tend to show up. A standard interior door will not maintain a fire separation, so ask your designer what door, frame and closer the drawings call for at any connection between the units.

Penetrations need the same attention. Ductwork, pipes and wiring that pass through the separating wall or ceiling have to be sealed so the separation still performs, using fire-stopping materials suited to each penetration. Ask your contractor how they plan to handle every penetration, and keep the number down by routing services thoughtfully at the design stage.

Each unit also needs a safe way out that does not depend on passing through the other unit, and smoke and carbon monoxide alarms. In a basement suite, if a window serves as an emergency exit, keep its window well clear of snow and debris through the winter. Your designer will lay out exits and alarm locations for both units, including where alarms must be interconnected.

Fire separation is expensive to fix after the fact, because it usually means tearing out finished drywall and starting again. Ask each contractor you are considering to explain how they build and inspect separating assemblies on secondary suites, and ask to see past permitted suite projects. If you have questions about your specific plan, contact the City's Building Code Services at buildingpermits@ottawa.ca. You can compare quotes from addition contractors in the Ottawa Construction Network directory.

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