Canadian building code question

What are the building code requirements for duplex buildings in Canada?

Duplexes must meet fire separation requirements between dwelling units, independent egress for each unit, sound transmission class (STC) ratings for demising walls and floors, and may need to comply with Part 3 or Part 9 depending on building size and configuration.

A duplex contains two dwelling units in a single building structure. The building code treats each unit as a separate fire compartment requiring fire separation, independent egress, sound insulation between units, and separate mechanical and plumbing services. Whether the duplex falls under Part 3 or Part 9 of the code depends on building area, height, and occupancy classification.

What to check first

  • Fire separation between dwelling units must meet minimum fire-resistance rating requirements.
  • Each dwelling unit requires independent egress to the exterior without passing through the other unit.
  • Demising walls and floors between units must meet STC and impact sound insulation requirements.

Jurisdiction notes

National baseline

The NBC sets fire separation, egress, and sound insulation requirements for buildings with two dwelling units.

Part 3 vs Part 9

Most duplexes fall under Part 9, but stacked configurations or larger buildings may trigger Part 3 requirements.

Municipal zoning

Zoning bylaws control where duplexes can be built and may impose additional design constraints beyond the building code.

Work through it in this order

  1. Determine whether the duplex falls under Part 3 or Part 9 based on building area and height.
  2. Confirm the fire-resistance rating required for the demising wall or floor between units.
  3. Verify that each unit has independent egress, smoke alarms, and carbon monoxide detection.
  4. Check STC and impact sound rating requirements for the assembly separating the two units.

Common questions

What fire separation is required between duplex units?

The demising wall or floor between units typically requires a minimum fire-resistance rating, commonly 1 hour, but this depends on building height and construction type.

Can a duplex share a furnace or water heater?

Each dwelling unit generally requires independent mechanical and plumbing services, but shared systems may be permitted in some configurations with proper separation.

What sound rating is required between duplex units?

The assembly separating dwelling units must meet the minimum STC rating specified in the code, typically STC 50 or higher.