What is the ACH target for Step Code 4?

Step Code 4 requires airtightness of 1.5 ACH@50Pa or better, measured by a blower door test.

When does Step Code 4 become mandatory in BC?

Step 4 is expected to become the provincial minimum for Part 9 residential buildings in 2027.

How much does it cost to build to Step Code 4?

Building to Step 4 typically adds 3% to 8% to construction costs compared to base code. FortisBC rebates of up to $15,000 per dwelling unit can offset a significant portion of this premium.

Aerial view of a residential home under construction showing wood framing and roof trusses

// BC Step Code Timeline

2023 Step 3 mandatory

2027 Step 4 expected

~2032 Step 5 target

BC Step Code 4: What Builders Need to Know

Key takeaway: Step 4 is expected in 2027. The target is 1.5 ACH50: 40% tighter than Step 3. FortisBC rebates up to $15,000 offset most of the incremental cost. Builders who start now are ahead.

What Step 4 Requires

Step 4 is performance-based. Three metrics verified through energy modelling and on-site testing:

Airtightness (ACH50): 1.5 air changes per hour at 50 Pascals or less. Down from 2.5 at Step 3. This is where most builders struggle, and where air sealing technology makes the biggest difference.

TEDI (Thermal Energy Demand Intensity): Varies by climate zone. In CZ5 (Okanagan, HDD ~3700): roughly 35 to 45 kWh/m2/year.

MEUI (Mechanical Energy Use Intensity): Total mechanical energy use. Equipment selection (heat pumps, HRVs) is critical here.

What Changes from Step 3

Airtightness gets 40% tighter. At Step 3, careful manual sealing usually works. At Step 4, conventional tape-and-caulk methods become unreliable. Many builders incorporate aerosol-based sealing that targets a specific ACH number.

Envelope performance improves. Higher effective R-values, better window U-values, more attention to thermal bridging. Typical: 2x6 walls with continuous exterior insulation.

Heat pumps become standard. Furnaces as primary heat sources make MEUI numbers very hard to hit. The FortisBC hybrid pathway (heat pump + gas furnace backup) qualifies for the highest rebate tier.

Energy advisor involvement increases. Getting involved at design stage saves thousands by optimizing envelope vs. equipment spending.

What It Costs

For a 2,000 sq ft home in the Okanagan: $8,000 to $20,000 over Step 3. Main drivers: windows ($3,000 to $8,000), insulation ($2,000 to $5,000), HVAC ($2,000 to $6,000), air sealing ($2,000 to $4,000).

FortisBC rebates up to $15,000 for Step 4. Combined with CleanBC, 50% to 80% offset is realistic. See our cost breakdown and rebate calculator.

How to Hit 1.5 ACH50

Start with air barrier design. Decide primary air barrier location before construction. Detail every penetration and transition on drawings.

Mid-construction blower door test. Optional by code, mandatory in practice at Step 4. Kelowna offers a $325 rebate. Fix leaks while the barrier is accessible. See our pre-drywall guide.

Seal systematically. Bottom plates, window rough openings, electrical penetrations, plumbing, attic transitions. These are where aerosol sealing excels.

The 2027 Timeline

BC has signaled Step 4 as the provincial minimum for Part 9 buildings in 2027. The specific Ministerial Order has not been signed as of early 2026, but the direction is clear. Some Metro Vancouver municipalities already require Step 4 or higher.

Municipality Requirements

For a phase-by-phase approach, see our Step Code 4 checklist.