Site & Design | Climate & Step Code
Kelowna Climate, Step Code, and the Overheating Rule
Kelowna is not Vancouver. Heating Degree Days of 3,715, summers hot enough that the BC Building Code now requires a designed indoor maximum, and a smoke season that runs one to three weeks per year. Designing an Okanagan multiplex off a Lower Mainland template is how pro formas break quietly — you pass permit and then spend the first summer fielding tenant complaints. This page covers the four code layers that actually bind: the 26 °C overheating rule, Energy Step Code, Zero Carbon Step Code, and the Part 9 vs Part 3 threshold.
Key Takeaways
- ✓Kelowna's design HDD is 3,715 — the number that sizes envelope, mechanical, and Step Code compliance.
- ✓New dwellings must be designed so at least one living space does not exceed 26 °C in summer. Active cooling is the practical answer on most infill lots.
- ✓The 2024 BC Building Code has applied in Kelowna since March 10, 2025. Every active permit since then is under the new code.
- ✓Part 9 covers residential up to 3 storeys and 600 m² building area. Most multiplex is Part 9 — but stacking 4-6 units can trip you into Part 3.
- ✓Wildfire smoke is now a design input. MERV-13 filtration and controllable make-up air are the minimum credible response.
Why Kelowna Designs Different
Kelowna sits in the northern edge of the Okanagan semi-arid belt. It is meaningfully colder than Vancouver in winter, meaningfully hotter in summer, and exposed to the dominant BC wildfire corridor. All three load the envelope differently. The published design HDD is 3,715 since September 12, 2023 — use that number, not a national default.
Heating Degree Days
3,715
Kelowna's HDD figure — the one that actually drives envelope and mechanical sizing. Effective since September 12, 2023 and published directly by the City (kelowna.ca Energy Step Code).
Summer Extreme
Hot & dry
Multi-day stretches above 35 °C are routine. The 2021 heat dome and subsequent summers pushed the BC Building Code to require a designed indoor maximum — hence the 26 °C rule.
Winter Cold Snap
Below -20 °C
Short but sharp. Heat-pump selection needs to hold capacity at cold ambient, which knocks out several otherwise-cheap single-head units.
Smoke Season
1-3 weeks/yr
Wildfire smoke drives PM2.5 to hazardous levels for days at a time. Filtration is no longer a nice-to-have in Kelowna — tenants ask about it.
The 26 °C Overheating Rule
The BC Building Code now requires that new dwelling units be designed so at least one living space does not exceed 26 °C in summer. The City of Kelowna publishes this requirement on its energy-efficiency page (kelowna.ca). It is a design-load calculation, not a field test — but it has to be demonstrated in the submission, and it changes how you spec windows, shading, and mechanical.
What it actually changes on the ground
- →West-facing glazing gets downgraded in area or upgraded in spec — cheap west-facing picture windows fail the calculation.
- →At least one living room per unit has to hit the 26 °C ceiling — so the floor plan has to nominate which room, and it usually isn't the one with the best view.
- →Active cooling is almost always the cost-effective path versus passive-only compliance. Heat-pump cooling doubles as heating.
Energy Step Code and Zero Carbon Step Code
BC runs two parallel ladders — one for energy efficiency, one for greenhouse-gas intensity. Both apply. Both get tighter over time. The current required step in Kelowna is set by local bylaw and moves, so pull the live number from the provincial Step Code requirements page before you spec the envelope.
Energy Step Code
Six-step performance ladder measuring envelope efficiency against modelled energy use. Steps tighten airtightness, insulation, and mechanical efficiency requirements. The province runs the framework; the City of Kelowna sets the step that applies for each building class.
Zero Carbon Step Code
Parallel four-level ladder that measures greenhouse-gas intensity. It sits alongside the Energy Step Code and is increasingly the binding constraint because it effectively rules out fossil-fuel heating at the higher levels.
Why Two Ladders
The Energy Step Code alone lets a super-efficient gas furnace pass. The Zero Carbon Step Code closes that loophole by measuring emissions directly. A Kelowna multiplex in 2026 needs to satisfy both.
The 2024 BC Building Code has applied in Kelowna since March 10, 2025 (City of Kelowna 2024 BCBC change bulletin). Any design that predates that bulletin has to be re-checked against the current rules.
Part 9 vs Part 3 Threshold
Part 9 of the BC Building Code covers housing and small buildings up to 3 storeys and up to 600 m² in building area (Province of BC 2024 BC Codes). Above either limit you are in Part 3 — the commercial and multi-unit residential code used for apartment buildings. Most Bill 44 SSMUH multiplex fits inside Part 9, but the 600 m² building-area ceiling is surprisingly easy to hit if you stack 4-6 larger units.
| Dimension | Part 9 (small buildings) | Part 3 (large & multi-unit) |
|---|---|---|
| Height | Up to 3 storeys | Above 3 storeys |
| Building area | Up to 600 m² | Above 600 m² |
| Structural design | Prescriptive paths allowed | Engineered design required |
| Fire separations | Standard residential assemblies | Heavier fire-resistance ratings |
| Typical multiplex fit | 3-4 unit infill, most 6-unit compact designs | Large 6-plex with generous floor plates, or any project on three full floors with big units |
Pushing into Part 3 adds meaningful structural, fire-separation, and accessibility cost. Check the building-area calculation at concept, not at permit.
Design Implications for Multiplex
The code layers above turn into a specific list of design moves. None of them are exotic — but they all have to be decided at concept, because retrofitting any of them later is expensive.
Heat pumps, not furnaces
Cold-climate air-source heat pumps are the default. Ducted vs ductless is a layout question; the performance requirement is that capacity holds at -15 °C design temperature. Gas-fired heating in new Kelowna multiplex is fighting the Zero Carbon Step Code for no real payback.
HRV/ERV with cooling capability
A passive HRV passes airtightness but fails overheating. ERVs recover moisture in winter and help manage summer load. Pair with heat-pump cooling to satisfy the 26 °C rule without a mid-summer emergency AC retrofit.
Low-SHGC glazing on west and south
West-facing glazing is the single largest overheating risk in the Okanagan. Solar Heat Gain Coefficient targets below 0.25 on west and south elevations, paired with higher SHGC on east and north if you want winter gain.
External shading & deep overhangs
Internal blinds do almost nothing for overheating — the heat is already through the glass. Fixed overhangs, deep reveals, and operable external shutters do the work. Design them in, don't bolt them on.
Cross-ventilation that actually works
Floor plans where every unit has openings on at least two orientations. Night flushing in summer only works if the air can move. This is a plan-layout decision, not a mechanical one.
Thermal mass, carefully
Exposed concrete slab edges, dense interior partitions in strategic rooms. Useful in Kelowna's diurnal climate — the overnight low does the work if the mass is there to absorb the afternoon peak.
The Wildfire Smoke Layer
Wildfire smoke is a design input in the Okanagan now, not a weather event. For the last several summers Kelowna has recorded at least one extended stretch of hazardous PM2.5. A multiplex with good envelope and mechanical specs can ride through those weeks without tenants opening windows — but only if the filtration and make-up air are designed in.
The minimum credible spec
- →MERV-13 filtration on the fresh-air side of the HRV/ERV — not just a better furnace filter.
- →Make-up air strategies that can be shut down during a smoke event without starving the building of ventilation for days.
- →Recirculation mode with enhanced filtration as a default, with a documented procedure tenants can trigger.
- →Operable window hardware that actually seals — cheap vinyl sliders leak smoke through the frame even when closed.
Smoke-event filtration also sells the unit. Tenants with young kids, asthma, or elderly parents ask about it during lease-up — especially after a bad smoke year.
Best For
- ✓ Part 9 multiplex designs that stay under 600 m² building area and 3 storeys — the sweet spot for SSMUH.
- ✓ All-electric mechanical with heat-pump space and water heating — cleanest path through the Zero Carbon Step Code.
- ✓ Floor plans where every unit gets cross-ventilation and a west-shaded living room for the 26 °C demonstration.
Usually Fails When
- ✕ The design lands at 610 m² building area and discovers at permit it is now Part 3 — structural and fire cost jumps.
- ✕ The overheating calculation is done as an afterthought and west-facing glazing has to be re-sized during DP review.
- ✕ Gas service is designed in "for flexibility" and the Zero Carbon Step Code level blocks it — wasted service upgrade cost.
What To Verify Before Spending Money
- → The building area calculation at concept, with a buffer below 600 m² if you are anywhere close.
- → The current Energy Step Code and Zero Carbon Step Code step required in Kelowna at filing date.
- → That the mechanical, ventilation, and filtration spec satisfies both the 26 °C rule and a realistic smoke-event scenario.
Frequently Asked Questions
Do I need air conditioning in a new Kelowna multiplex?
Does a multiplex qualify as Part 9 or Part 3 of the BC Building Code?
Which Energy Step Code and Zero Carbon Step Code step does Kelowna require for a new multiplex?
How does the overheating rule change window selection?
Does the Infill Fast-Track path still need Step Code compliance?
What is the Zero Carbon Step Code and why does it matter for a multiplex?
Official Sources Referenced
Screen Your Kelowna Lot for Multiplex
Enter any Kelowna address to check SSMUH unit count, zoning, frequent-transit bonus eligibility, and whether the Infill Fast-Track path applies.