Every new home in British Columbia, including every unit in a multiplex, must have at least one living space designed to stay at or below 26°C on a summer design day. The rule is in the BC Building Code 2024 and applies to any project whose building permit was applied for on or after March 8, 2024. The cooling has to be built into the home, and each dwelling unit, including a suite, needs its own room.
For a fourplex that is four rooms, four cooling calculations, and four pieces of equipment or four passive designs that a designer has to prove on paper before the permit is issued. It is one of the quieter cost lines in a multiplex budget, and one of the easiest to get wrong late.
Where the rule came from
The summer of 2021 killed 619 people in British Columbia during the heat dome. The report to the Chief Coroner, “Extreme Heat and Human Mortality: A Review of Heat-Related Deaths in B.C. in Summer 2021,” recommended that the 2024 edition of the code “incorporate both passive and active cooling requirements in new housing construction.”
The province answered with a maximum design temperature for one living space in each dwelling unit. The Building and Safety Standards Branch explained the provision in Information Bulletin B24-08, dated April 19, 2024. The bulletin says the requirement applies to new dwelling units “in all large (Part 3) and smaller (Part 9) residential occupancies.” Part 9 is where houses, duplexes and the wood-frame multiplexes on residential lots sit.
The bulletin describes the designated room as “a place of reprieve for occupants of the dwelling unit from elevated temperatures.”
What counts as a living space
The code does not define “living space,” but the bulletin draws the line using Article 9.33.3.1. On the wrong side of that line: unfinished basements, service rooms, ancillary spaces, exits, heated crawl spaces, bathrooms, laundry rooms, closets and pantries. On the right side: a room where a person can spend an extended period and continue daily life.
The designer chooses the room. It does not have to be a bedroom. The bulletin says the choice should make sense for “the circumstances of the dwelling unit (climate, configuration, building systems, etcetera).” In an adaptable unit the protected room should be one of the spaces designated as adaptable.
One room per dwelling unit is the minimum. The bulletin’s own question-and-answer section deals with the multiplex case head on:
Can a common space (i.e. laundry room) shared between two dwelling units (i.e. secondary suite) be used as a cooling room to satisfy the new overheating provisions? No. Each dwelling unit requires its own living space capable of maintaining an indoor design temperature of not more than 26°C.
A fourplex with a lock-off suite in one unit therefore needs five protected rooms, because the suite is a separate dwelling unit.
Mechanical cooling: what qualifies and what does not
The bulletin lists ducted air conditioning, ductless mini-split air conditioners, heat pumps and geothermal systems as equipment that can meet the provision. Then it closes the door most people were hoping to walk through:
Plug-in units such as air-conditioning insert units installed in window openings are not considered to meet the new provisions. If mechanical cooling systems are required, the mechanical cooling equipment is to form part of a system that is integral to the building.
In practice this pairs with the heating side. A heat pump is already the default heating system on a new BC multiplex, and a heat pump that heats in winter can cool in summer. A ductless head in the living room of each unit, sized for that room, is the most direct route. The bulletin also points out that heat-recovery ventilators and heat pumps can serve the cooling target and the Energy Step Code target at the same time, as long as somebody coordinates the two.
Passive design is allowed, if you can prove it
Mechanical cooling is one route. The bulletin says passive strategies “may be used as an alternative or a supplement to mechanical cooling where it can be shown that the passive design measures can help limit the maximum indoor design temperature to 26°C.” Its list:
- building orientation that reduces unwanted solar gain and allows natural ventilation
- a better-performing envelope, with a warning that a tighter, better-insulated building can hold heat and must be paired with ventilation or cooling
- fixed or operable exterior shading: overhangs on the south, vertical shading on the east and west, sliding shade panels, exterior roll shutters
- glazing with a solar heat gain coefficient chosen for cooling as well as heating
- window placement and window-to-wall ratio, with a recommendation to minimize glass on east and west walls
- operable windows placed for cross ventilation and for venting warm air from upper storeys at night
- thermal mass such as concrete, stone or brick inside the unit
- reflective or green roofs
The word “shown” is doing the work in that sentence. A passive design is accepted when the calculation shows the room holds at 26°C on the design day. On a narrow Vancouver lot with the long walls facing east and west and neighbours on both sides, that calculation is hard to win, so budget for a mechanical head in the protected room unless the calculation says otherwise.
The calculation the permit needs
For Part 9 buildings the code names the method. Sentence 9.33.5.1.(1) requires that peak cooling loads be determined under CSA F280. The bulletin adds that HOT2000, the energy modelling program used for Step Code compliance, “would not be appropriate” for proving the 26°C target because of its limits in predicting cooling loads. A list of software verified for CSA F280 is kept by HVAC Designers of Canada.
The outdoor conditions for the calculation come from Appendix C of the code, using the July 2.5 percent dry-bulb design temperature for the location, unless the local government has set its own climatic values. The bulletin is candid that these are historical files, “not projections of future extended heat waves or extreme heat events.”
Division C, Sentence 2.2.2.1.(1) requires that “sufficient information shall be provided to show that the proposed work will conform to this Code.” For this rule, that means the permit set has to show which room in each unit is protected and how the 26°C target is met, through the CSA F280 calculation.
A follow-up industry guide fills in the method. HVAC Designers of Canada and the Thermal Environmental Comfort Association published the Guideline on Single Zone Cooling in Dwelling Units, version 1.0a, on March 14, 2025, with input from BC Housing, the Building and Safety Standards Branch and the Canadian Home Builders’ Association of BC. It is a voluntary good-practice guide, and it sets the design temperature of the cooling zone itself at 24°C for the purpose of sizing the equipment, with the outdoor design temperature drawn from the same Appendix C July 2.5 percent values. It applies only where a single room is cooled; a whole-unit system sized under CSA F280 satisfies it automatically.
What this means for a multiplex budget and schedule
Get the calculation done early. The bulletin recommends the CSA F280 work be done “as early in the design process as possible” by a mechanical consultant, contractor or someone competent in HVAC design, and it recommends an integrated design process so the envelope, glazing and mechanical decisions are made together. On a multiplex, the room you protect, the window you shade and the wall you run refrigerant lines through are all fixed by the time the drawings go in.
Count the units, then count the rooms. Four units means four protected rooms and four sets of equipment or four proven passive designs. A lock-off suite adds one more.
Choose the room with the orientation in mind. A living room on a west wall behind a big window is the hardest room in the building to hold at 26°C. A bedroom on the north side may cost less to protect. The bulletin leaves the choice to the designer, and the choice changes the equipment size.
Plan the wiring and the drain. Ductless heads need a refrigerant line, a condensate drain and a circuit. A BC Hydro service upgrade already sets electrical capacity for the building; the cooling load is part of that number.
Vancouver runs its own by-law. Inside the City of Vancouver the Vancouver Building By-law governs rather than the provincial code. Confirm the matching clause in the edition your permit falls under before assuming the provincial wording applies word for word.
What a buyer should ask
If the home was permitted on or after March 8, 2024, one room in it was designed to hold 26°C. Ask which room. Ask whether the cooling is a fixed system or a passive design, and if it is passive, ask to see the calculation. The same rule applies in Kelowna and on the coast; only the Appendix C design temperature changes with the location.
Sources: Building and Safety Standards Branch, Province of British Columbia, Information Bulletin No. B24-08, “Protection from Overheating in Dwelling Units,” April 19, 2024; HVAC Designers of Canada and Thermal Environmental Comfort Association, “Guideline on Single Zone Cooling in Dwelling Units,” Version 1.0a, March 14, 2025; BC Building Code 2024, Division B Sentences 9.33.2.1.(2), 9.33.3.1.(2) and 9.33.5.1.(1) and Division C Sentence 2.2.2.1.(1), as cited in those documents. All read September 17, 2026.
David Babakaiff, Co-Founder, VanPlex | PlexRank™ | Profit with Multiplex
