How the BC Building Code treats duplexes, triplexes, fourplexes and sixplexes

Which code, and which part of it

The BC Building Code 2024 came into effect on 8 March 2024 and applies to projects with building permits applied for after that date. Its earthquake design and adaptable dwelling unit rules apply to permits applied for on or after 10 March 2025, and the province extended the date for qualifying in-stream projects to 8 March 2027. The province's code page also says BC Codes do not apply in the City of Vancouver, which has its own building bylaw. The unit-types chapter of the multiplex design guide covers Vancouver's adaptable unit rule.

The code is split into parts. Part 9 covers buildings of 3 storeys or less in building height, with a building area of no more than 600 square metres, used for residential and some other occupancies (Division A, Article 1.3.3.3). Building area means the largest horizontal area of the building above grade, measured to the outside of the exterior walls. Part 3 covers residential buildings over 600 square metres in building area or over 3 storeys (Article 1.3.3.2). The province's policy manual says most small-scale multi-unit buildings will likely fall under Part 9, and some may fall under Part 3 depending on size and number of storeys.

A firewall can change the count. Article 1.3.3.4 says that where a firewall divides a building, each portion counts as a separate building. A firewall is a fire separation of noncombustible construction, meaning materials that do not burn, that keeps its structure during a fire for its rated time. A long row of attached homes can be divided this way so each portion stays within the Part 9 limits.

Height is the other limit. The policy manual notes that a building over 3 storeys usually needs a second exit under the code, which it says has a large effect on project cost and viability. That is why the province recommends that cities allow at least 3 storeys and 11 metres in the zones its small-scale housing law covers.

Fire separation between homes

A fire separation is a wall, floor or ceiling built to slow the spread of fire, and its fire-resistance rating is the time it is tested to hold. Article 9.10.9.15 requires each suite to be separated from adjoining suites by a fire separation rated at least 45 minutes. Article 9.10.9.16 sets the same 45 minutes for suites in residential occupancies, which covers the homes in a multiplex.

Homes with more than one level need more. Sentence 9.10.9.16 (3) requires a dwelling unit of 2 or more storeys, counting a basement, to be separated from the rest of the building by a fire separation rated at least 1 hour. The same 1-hour rule applies around a house with a secondary suite, including its common spaces.

Inside a house with a secondary suite, the rating between the two homes depends on the smoke alarms. Sentence 9.10.9.16 (4) allows 15 minutes when every smoke alarm in the house is photo-electric and interconnected, 30 minutes when added photo-electric alarms are interconnected between the homes, and 45 minutes when neither applies. No rating is required when the building is sprinklered. Interconnected means that when one alarm sounds, the linked alarms sound too.

Between separate buildings, the code uses distance. The province's policy manual explains that spatial separation rules stop fire spreading from one building to another, that the code can allow a building right up to the property line in some cases, and that the required distance can be larger than a zoning setback.

Smoke alarms, fire alarm systems and sprinklers

Article 9.10.19.1 requires smoke alarms in each dwelling unit, and in the common spaces of a house with a secondary suite. Where a home needs more than one smoke alarm, Article 9.10.19.5 requires them to be interconnected so that one alarm sets off every alarm in that home.

A fire alarm system is a building-wide system, separate from the smoke alarms inside each home. Article 9.10.18.2 requires one in a building of more than 3 storeys, counting storeys below the first storey, and where the residential occupant load is more than 10 people in sleeping accommodation. Sentence (5) then removes the requirement for a residential building where an exit or public corridor serves no more than 4 suites, or where each suite has direct access to an exterior exit leading to ground level. A multiplex where each home has its own door to the outside meets the second test.

The Part 9 articles read for this chapter treat sprinklers as a design choice that changes other requirements. Article 9.10.1.3 says sprinkler systems in Part 9 buildings follow named Part 3 articles. Article 9.9.10.1 removes the bedroom escape window requirement where the suite is sprinklered. Sentence 9.10.9.16 (4) removes the rating between the two homes in a sprinklered house with a secondary suite. And the policy manual says sprinklers or design changes can help a building meet the code's fire distance rules where zoning setbacks are small.

The manual also notes that some local governments hold authority to set technical building requirements that differ from the provincial code. Vancouver is the clearest case. The city's building department confirms what applies to a given lot.

Article 9.10.20.3 adds one site rule: access for fire department equipment must be provided to each building by a street, private roadway or yard. For a rear building on a lot, the route from the street is part of the design from the start.

Exits from each home

Article 9.9.9.2 deals with homes whose door opens onto a public corridor or exterior passageway. From that door it must be possible to go in opposite directions to 2 separate exits, unless the home has a second and separate way out. In a house with a secondary suite, that rule is relaxed if the building is sprinklered or if each home has direct access from each storey to a balcony or to an openable window of the size the code sets.

Article 9.9.9.3 requires a second way out where a home's door opens onto a shared exit stair, a corridor with a single exit, or a raised shared passageway or balcony with a single stair. Homes with their own outside doors avoid those shared routes.

Bedrooms have their own rule. Unless the suite is sprinklered, Article 9.9.10.1 requires each bedroom to have at least one outside window or door that opens from the inside without keys or tools. The window must give an unobstructed opening of at least 0.35 square metres, with no dimension under 380 millimetres. Where it opens into a window well, 760 millimetres of clear space is required in front of it.

Sound between homes

Sound transmission class, or STC, rates how well a wall or floor assembly blocks airborne sound, measured in a laboratory under the test standard ASTM E90. Apparent sound transmission class, or ASTC, rates the separating wall or floor together with the walls, floors and ceilings joined to it, measured between rooms in a building under ASTM E336 or calculated by the code's method. ASTC counts sound that travels around the separating wall through the joined parts.

Article 9.11.1.1 requires each dwelling unit to be separated from every other space in the building where noise may be made by either an ASTC rating of at least 47, or a separating assembly with an STC rating of at least 50 plus joined constructions that meet Article 9.11.1.4. Construction between a home and an elevator shaft or garbage chute must reach STC 55.

A house with a secondary suite has a lower bar. Sentence 9.11.1.1 (2) accepts STC 43, ASTC 40, or a listed build: joist spaces filled with at least 150 millimetres of sound-absorbing material, stud spaces filled, a resilient channel on one side at 400 or 600 millimetre spacing, and 12.7 millimetre gypsum board on ceilings and both sides of walls.

Section 9.11 of the code covers airborne noise only. The sound separation Journal post on this site covers footstep noise and the other sounds that are left to the designer.

Accessibility and adaptable homes

Article 9.5.2.1 says every Part 9 building must be designed to Section 3.8, the code's accessibility section, except as Articles 9.5.2.3 and 3.8.2.1 provide. Article 3.8.2.1 exempts detached houses, semi-detached houses, houses with a secondary suite, duplexes, triplexes, townhouses, row houses and boarding houses. Those buildings, including their secondary suites, must still provide at least one bathroom with the walls next to the toilet and the shower or bath reinforced for grab bars to be added later (Sentence 3.8.5.1 (2)).

Fourplexes and sixplexes are absent from that list. For those buildings, the designer works through Section 3.8 with the local building official, and the answer depends on the layout.

Adaptable dwelling units are homes built with some accessible features and room to add more later. The province's accessibility page says that since 10 March 2025, at least 1 in 5 units must be adaptable in large condominium and apartment buildings and on the first floor of smaller apartments and condominiums. The same page says the rule does not reach units of more than two storeys, units with a separate entry or exit to the outside, or units not reached by an interior accessible corridor. In the code, Article 3.8.5.1 applies the rule to one-storey homes served by an accessible interior public corridor and an accessible common building entrance.

The policy manual states the practical result: Part 9 buildings without common entrances or elevators, such as townhouses and rowhouses, are not required to meet the adaptability provisions.

Energy, carbon, cooling and earthquakes

The BC Energy Step Code, created in 2017, sets energy efficiency targets for new buildings in steps, and a higher step means a more efficient building. The first step up came in May 2023, when most new buildings had to be 20 percent more energy efficient than the 2018 minimums. Steps 1 and 2 for smaller buildings are now listed as Reserved in the BC Building Code and no longer meet the minimum. The province's stated path is net-zero energy ready new buildings by 2032, and cities may require higher steps by bylaw. The Step Code needs a digital whole-building energy model before the design is final.

The Zero Carbon Step Code sets limits on emissions from space heating and hot water, in four steps from EL-1 (measure only) to EL-4 (zero carbon performance). Since 10 March 2025 the province has required most new buildings to meet at least EL-1, and cities can require any step. For Part 9 buildings such as rowhomes and small apartment buildings, builders may follow a prescriptive path, which requires lower-carbon equipment for space heating, water heating or cooking, with more of it at higher steps, or a performance path with an emissions target.

Two B.C. changes took effect in March 2024: a cooling rule requiring one living space that does not exceed 26 degrees Celsius, and more complete wording for the rough-in of a radon subfloor depressurization system, which is piping that lets air be drawn from under the floor to keep radon gas out of the home.

New earthquake design rules apply to permits applied for on or after 10 March 2025. The policy manual says little to no effect on overall building size is expected for Part 9 buildings.