What are the fire separation requirements for drywall in a Toronto semi-detached or row house shared wall?

The shared wall (party wall) between units in a Toronto semi-detached or row house must achieve a minimum 1-hour fire resistance rating under the Ontario Building Code, which requires specific drywall assemblies — typically two layers of 5/8-inch Type X drywall on each side of the framing. This fire separation requirement exists to prevent fire from spreading between dwelling units, giving occupants time to evacuate and fire services time to respond.

The 1-hour fire resistance rating is a performance standard, meaning the wall assembly as a whole must withstand fire exposure for at least 60 minutes before failure. The specific drywall configuration depends on the framing type. For standard single-stud party walls (common in older Toronto semi-detached homes in neighbourhoods like Leslieville, the Danforth, Roncesvalles, and the Junction), achieving a 1-hour rating typically requires two layers of 5/8-inch Type X drywall on each side — four layers total. Each layer must be screwed with the joints staggered between layers, and all joints must be fully taped and finished with joint compound.

For staggered-stud party walls (more common in newer construction and renovations), a 1-hour rating can be achieved with one layer of 5/8-inch Type X drywall on each side, with the staggered studs providing the additional fire resistance through separation. Mineral wool insulation in the cavity further enhances both fire resistance and sound isolation.

Sound Transmission Requirements

The party wall must also meet STC 50 (Sound Transmission Class 50) under the Ontario Building Code, which governs sound transmission between dwelling units. Fire-rated assemblies and sound-rated assemblies often go hand in hand, since the same design principles — mass, air space, and decoupling — serve both purposes.

A common GTA party wall assembly that meets both the 1-hour fire rating and STC 50 consists of double 5/8-inch Type X drywall on resilient channel on one side, standard 5/8-inch Type X drywall on the other side, mineral wool insulation in the cavity, and all joints taped and sealed with acoustical sealant at the perimeter. This assembly can achieve STC 52–56 depending on construction quality.

The installation of resilient channel is a critical detail that must be done correctly. Resilient channel is a thin metal furring strip that decouples the drywall from the framing, breaking the rigid connection that transmits sound vibrations. The drywall screws must go only into the resilient channel — never through the channel into the stud behind. A single screw that short-circuits the resilient channel creates a rigid bridge that can reduce the STC rating by 10–15 points, effectively negating the entire sound isolation benefit of the assembly.

Maintaining the Fire Separation During Renovations

If you're renovating a semi-detached or row house in Toronto, maintaining the party wall fire separation is a critical code requirement that building inspectors will specifically check. Common renovation activities that can compromise the fire separation include:

Electrical work — running new wiring through the party wall requires fire-rated electrical boxes (or putty pads around standard boxes) and fire caulking around all penetrations. Standard electrical boxes create a gap in the fire separation that can allow fire to pass through in minutes rather than the required 60.

Removing or modifying drywall on the party wall — if drywall on the party wall is damaged, cracked, or needs to be replaced, the replacement must match or exceed the original fire-rated assembly. You cannot replace Type X drywall with standard drywall and maintain the fire rating.

Plumbing and HVAC penetrations — any pipe, duct, or mechanical connection that passes through the party wall must be sealed with approved fire stop materials. Expanding foam is not an acceptable fire stop — ULC-listed fire caulking, fire stop collars, or intumescent sealants are required.

The cost for drywall work on a party wall fire separation depends on the scope. Replacing damaged Type X drywall on one side of a typical semi-detached party wall runs $2,000–$5,000 for materials and labour. If the entire party wall assembly needs to be upgraded to meet current code — which is sometimes required during major renovations — the cost can reach $5,000–$12,000 including double layers of Type X, resilient channel, insulation, and fire stopping at all penetrations.

For any renovation work involving the party wall in a Toronto semi-detached or row house, a building permit is required. The City of Toronto inspector will verify that the fire separation is maintained and that all penetrations are properly fire-stopped. Get matched with a drywall contractor experienced in fire-rated party wall assemblies through Toronto Drywall Installers — this is specialized work where proper installation is literally a life-safety issue.