Who decides which fire separation route fits my Nepean suite?

The City of Ottawa decides, through the building permit review for your secondary suite.

Ontario's Building Code sets out two routes for separating dwelling units in a house with a secondary suite. One is a fire separation with a 45-minute rating (clause 9.10.9.16.(1)). The other is a continuous smoke-tight barrier of 5/8-inch (15.9 mm) Type X drywall on both sides of the shared walls and on the underside of the floor-ceiling framing between the units (clause 9.10.9.16.(4)). The Code waives the Type X barrier route where the house is sprinklered throughout (clause 9.10.9.16.(5)); ask the City how that applies. These are minimums for new work, and the City tells you through the permit how they apply to your renovation.

For an existing house, the Code also includes a compliance alternative under Part 11. Alternative C156 accepts a 15-minute horizontal fire separation where smoke alarms are installed in every dwelling unit and common area and are interconnected. The Code text we have does not describe which assembly gives 15 minutes; ask the City.

The City's adding-an-apartment page says a building permit is required before any work starts, even where little or no construction is proposed, because the change of use has to be reviewed. The drawings submitted with the permit application must show the wall construction and the floor-ceiling construction between the new unit and the main dwelling and common areas.

The drywall angle matters here because the fire separation or smoke-tight barrier must be continuous under clause 9.10.9.2. So openings in the shared ceiling, such as pot lights or ducts, matter; ask the City about them before the ceiling is closed. Light-frame walls, columns, arches and beams that carry floors between the units are also protected by not less than 5/8-inch Type X drywall under clause 9.10.8.3.(2).

A shared service room with fuel-fired appliances has its own option under clause 9.10.10.4.(2)(b): lining both sides of its walls and the underside of the floor-ceiling with 5/8-inch Type X instead of building a full one-hour service room.

Before you hire anyone, ask the City's Building Code Services which route your house can use, with your floor plan and a description of the existing wall and ceiling construction in hand.