What ACH50 Target Do You Need for BC Step Code 3, 4, or 5?
Key takeaway: Step Code 3 requires 2.5 ACH50 (current BC minimum). Step Code 4 requires 1.5 ACH50 (expected provincially January 2027). Step Code 5 requires 1.0 ACH50 (net-zero ready). Targets are the same in every BC climate zone; what changes by climate is wall and window spec, not the airtightness number.
ACH50 quick reference table
| Step Code Level | ACH50 Target | Status in BC |
|---|---|---|
| Step 1 | No airtightness requirement | Phased out |
| Step 2 | 3.0 ACH50 | Phased out in most municipalities |
| Step 3 | 2.5 ACH50 | Current provincial minimum for Part 9 (since 2022-2024 by municipality) |
| Step 4 | 1.5 ACH50 | Expected provincial minimum January 2027 |
| Step 5 | 1.0 ACH50 | Optional (net-zero ready) |
| Passive House (reference) | 0.6 ACH50 | Voluntary certification, separate test protocol |
These targets apply uniformly across BC. A house in Kelowna, Whistler, or Prince Rupert all need to hit 2.5 ACH50 to meet Step 3, even though the wall and window specs to model compliant overall energy use vary significantly by climate zone.
What does ACH50 actually mean?
ACH50 stands for air changes per hour at 50 Pascals of pressure. A blower door fan depressurizes the house to 50 Pa (roughly the equivalent of a 20 mph wind hitting every wall). The fan measures how much air flows through to maintain that pressure. Divide that airflow by the interior volume of the house and you get ACH50.
A reading of 2.5 ACH50 means the house exchanges its full air volume 2.5 times per hour under that test pressure. A reading of 1.5 ACH50 means 1.5 times per hour, which is 40% less air leakage than 2.5 ACH50.
ACH50 is a standardized test condition number, not what your house actually does on a typical winter day. Real-world infiltration is typically 1/20th of the ACH50 number, so a house at 2.5 ACH50 sees roughly 0.125 actual ACH at average wind and temperature conditions.
Which target do you need for your specific project?
The answer depends on your municipality, your build type, and whether you want to capture rebates above the minimum.
If you’re building right now (April 2026), at minimum:
| Where you’re building | Minimum ACH50 today |
|---|---|
| Most of BC (provincial Part 9 baseline) | 2.5 (Step 3) |
| Whistler | 1.5 (Step 4 since January 2024) |
| Vancouver | 1.5 (Step 4 effectively, plus Zero Carbon) |
| Burnaby | 2.5 (Step 3) plus Zero Carbon EL-4 |
| Surrey | 2.5 final + 4.0 mid-construction (Step 3 plus EL-1) |
A handful of municipalities including Vancouver, Whistler, and several North Shore communities are already at Step 4. Most of BC is still at Step 3 as of April 2026.
If you’re building for January 2027 occupancy or later:
The provincial minimum is expected to advance to Step 4 (1.5 ACH50) in January 2027. Builds permitted close to or after that date should design for 1.5 ACH50, not 2.5. The cost of designing-down later is significant; designing-up at the start is cheap.
If you’re capturing FortisBC rebates:
The FortisBC New Home Program rewards builds above the provincial minimum:
| Performance level | FortisBC rebate per dwelling unit |
|---|---|
| Step 3 (2.5 ACH50) | $0 (provincial minimum, no rebate) |
| Step 4 (1.5 ACH50) | $9,000 to $15,000 (with hybrid heat pump) |
| Step 5 (1.0 ACH50) | $11,000 to $20,000 (with hybrid heat pump) |
If you’re already going to install a hybrid heat pump and exterior insulation, the marginal cost to design and build for Step 4 instead of Step 3 is often less than the rebate. Run the math on your specific project with the rebate calculator.
What it takes to hit each target
The cost and complexity to reach each level scales non-linearly. Going from Step 3 to Step 4 is more than twice as hard as going from Step 2 to Step 3.
Step 3: 2.5 ACH50 (current minimum)
| Element | Typical spec |
|---|---|
| Wall (CZ5) | R-22 cavity + R-7.5 exterior |
| Windows | U-value 1.4 W/m²K (double-pane low-E with argon) |
| Air sealing | Disciplined manual sealing (caulks, foams, tapes) |
| Mechanicals | High-efficiency furnace or air-source heat pump |
| HRV | 70%+ sensible recovery |
| Cost premium | 1 to 3% over base code |
Step 3 is achievable with manual sealing if the framing crew is disciplined and the air barrier strategy is drawn before framing starts. Most experienced Okanagan builders hit 2.5 ACH50 reliably.
Step 4: 1.5 ACH50 (expected 2027)
| Element | Typical spec |
|---|---|
| Wall (CZ5) | R-22 cavity + R-7.5 to R-10 exterior |
| Windows | U-value 1.2 to 1.4 W/m²K |
| Air sealing | Manual baseline + aerosol pass typical |
| Mechanicals | Hybrid heat pump (gas backup) or full electric |
| HRV | 75%+ sensible recovery |
| Cost premium | 4 to 7% over base code |
The 40% drop from 2.5 to 1.5 ACH50 is where most builders need a deliberate change in approach. Manual sealing alone delivers 1.5 ACH50 about 30 to 40% of the time on Okanagan custom builds; aerosol-supplemented seals deliver it about 92% of the time (see case studies).
Step 5: 1.0 ACH50 (net-zero ready)
| Element | Typical spec |
|---|---|
| Wall (CZ5) | Double-stud or R-22 + R-15 exterior |
| Windows | U-value 0.8 W/m²K (triple-pane standard) |
| Air sealing | Continuous membrane + aerosol pass + mid-construction test mandatory |
| Mechanicals | All-electric, cold-climate ASHP |
| HRV | 80%+ sensible recovery |
| Cost premium | 8 to 15% over base code |
Step 5 is overkill for most builders today. It makes sense for custom homes where comfort and operating cost are sold features, off-grid sites where mechanical complexity is expensive to service, or builders piloting Step 5 to position for the post-2032 timeline.
How is ACH50 tested?
A registered energy advisor performs the test, typically at two points in the build:
Mid-construction (optional, recommended): Performed at the pre-drywall stage, after rough-in is complete and the air barrier is fully detailed but before drywall closes everything in. The point is to find leaks while they’re still cheaply accessible. The City of Kelowna offers a $325 rebate for mid-construction tests. See pre-drywall air sealing.
As-built (mandatory): Performed after construction is complete and before occupancy. This is the official compliance test. The result becomes part of the as-built compliance report submitted with the occupancy application.
The test itself takes 60 to 90 minutes per house. The fan mounts in an exterior door opening, the house is depressurized to 50 Pa, and the energy advisor records the airflow. Multiple readings are taken at different pressures to derive the official ACH50 number.
Common reasons builds miss their target
If your blower door comes back at 1.8 instead of 1.5, or 2.8 instead of 2.5, the post-mortem usually identifies one of these:
- Bottom plate to subfloor seal. Single largest source of air leakage in BC homes. Glue-and-screw the plate or use a sill gasket.
- Window rough openings. Backer rod plus low-expansion foam plus interior air seal. The interior side often gets skipped.
- Service penetrations. Plumbers and electricians cut through the air barrier without resealing.
- Attic-to-wall transitions. Interior partition tops opening to vented attic create direct air paths.
- Rim joist gaps. Spray foam stops short, gaps at corners.
- Recessed lighting. Non-IC-rated cans in insulated ceilings.
- Attic hatches. No gasket, no insulation.
See common air leaks for the full diagnostic inventory.
What if your build comes in over the target?
If the as-built blower door reading exceeds your target, you have a few options:
- Find and fix the largest remaining leaks manually. Possible but expensive after drywall and finishes are in. Cost typically runs $3,000 to $10,000 plus schedule delay
- Apply AeroBarrier as a remediation pass. Possible even with finishes in, with extra masking. Higher cost than a pre-drywall seal but salvages the project
- Request a Step level downgrade. If you targeted Step 4 and missed, you may still pass Step 3. You lose the FortisBC rebate but the build can still occupy
Avoiding all of this is the case for the pre-drywall blower door test. Catch leaks while they’re still cheaply accessible.
Frequently asked questions
Is 2.5 ACH50 hard to hit?
For an experienced framing crew with a drawn air barrier strategy and standard manual sealing, 2.5 ACH50 is achievable on most Okanagan wood-frame builds. The pass rate among disciplined crews is roughly 80 to 90%. The 10 to 20% miss rate usually traces to bottom plate seals or window rough openings.
Is 1.5 ACH50 achievable without aerosol sealing?
Sometimes, on simple geometries with very disciplined crews. The published Okanagan miss rate for manual-only Step 4 attempts is roughly 60 to 70%. Aerosol-supplemented seals deliver Step 4 about 92% of the time. For complex custom builds, aerosol sealing is the practical path.
Does a tighter house need more ventilation?
Yes. At Step 3 and below, mechanical ventilation (HRV or ERV) becomes essential because the building no longer leaks enough air to provide passive ventilation. The HRV requirement is part of Step Code mechanical specs, not separate from them. See HVAC for Step Code.
Can I get a different ACH50 target if my house is unusual (e.g., very large, very small)?
No. The Step Code airtightness targets are the same for all Part 9 buildings regardless of size. BC also allows Normalized Leakage Area (NLA) and Normalized Leakage Rate (NLR) as alternate metrics that account for surface area, but most projects use ACH50 because it’s simpler and matches the blower door test directly.
What if my municipality is at a different Step than the province?
Whistler is at Step 4 (1.5 ACH50) since January 2024. Vancouver is effectively at Step 4 with Zero Carbon requirements. Some municipalities like Burnaby require Step 3 plus carbon performance levels. Check your specific municipality’s requirements via the municipality guides before designing.
How does the BC Step Code ACH50 test compare to Passive House?
BC Step Code uses ACH50 measured at 50 Pa with the standard ASTM E779 protocol. Passive House uses ACH50 measured under a different (slightly stricter) protocol. The numbers aren’t directly comparable but they’re close enough that most Passive House projects also meet Step Code 5 by a comfortable margin.
Next steps
- Run the rebate calculator for your project numbers
- See aerobarrier case studies for real Okanagan ACH50 results
- Read how to achieve 1.5 ACH50 in wood frame construction for the full Step 4 build sequence
- Compare air sealing methods for your target level