How to Achieve Step Code 4 and 5

The problem: Step 4 requires 1.5 ACH50. Step 5 requires 1.0. Most builders can’t get there with traditional air sealing methods alone.

The Results Gap

The gap between Step 3 and Step 4 airtightness is larger than it looks. Going from 2.5 ACH50 to 1.5 ACH50 means sealing 40% more air leakage. That’s the difference between “good enough with careful detailing” and “every joint, penetration, and transition must be sealed perfectly.”

Here’s what typical blower door results look like by method:

Method	Typical Result	Step 3 (2.5)	Step 4 (1.5)	Step 5 (1.0)
Caulk and tape only	1.8 - 3.5 ACH50	Sometimes	Rarely	No
Spray foam + careful detailing	1.0 - 2.5 ACH50	Yes	Sometimes	Rarely
Aerosol sealing (AeroBarrier)	0.2 - 1.0 ACH50	Yes	Yes	Yes

The numbers tell the story. Traditional methods can hit Step 3 targets reliably. At Step 4, they become inconsistent. At Step 5, they almost never get there without significant rework.

Why Aerosol Sealing Works

Aerosol sealing works differently from every other air sealing method. Instead of a person finding and sealing gaps by hand, the building is pressurized and aerosolized sealant particles are released inside the envelope. The particles are carried by the airflow to every gap and crack, sealing from the inside out.

Four things make it different:

1. It finds invisible leaks. Pressurization forces sealant particles to every gap, including ones no inspector would ever find visually. Electrical boxes, framing connections, window rough openings, pipe penetrations, and the hundreds of small gaps that add up to a failed test.

2. Computer-controlled precision. Real-time monitoring tracks ACH50 during the seal. You watch the number drop and stop at your exact target. No guessing, no “we think it’ll pass.”

3. Consistent results. The method doesn’t depend on individual skill or crew experience. The physics of pressurized sealing are the same every time. That’s why typical results range from 0.2 to 1.0 ACH50, well within Step 4 and Step 5 targets.

4. You know before the EA arrives. The real-time monitoring during aerosol sealing effectively IS a blower door test. By the time your energy advisor arrives for the official test, you already know your number.

The Cost Math

AeroBarrier aerosol sealing typically costs $2,000 to $4,500 for a Part 9 residential home. Factor this into your overall cost of compliance calculations alongside FortisBC rebates.

That sounds like a significant line item. But consider what happens if you miss your Step 4 target by 0.3 ACH:

• Lost FortisBC rebate: $9,000 to $15,000 (hybrid heat pump pathway)
• Remediation costs: $3,000 to $10,000 for post-construction leak sealing
• Project delays: 2 to 6 weeks for diagnostic testing, remediation, and retest
• Retest fees: $400 to $600 per blower door retest

The ROI calculation is straightforward: spend $2,000-$4,500 upfront to protect $9,000-$15,000 in rebates and avoid $3,000-$10,000 in remediation risk.

When to Use Each Method

Caulk and tape: Use for Step 3 builds where 2.5 ACH50 is the target. Effective when crews are experienced and detailing is thorough. Lower cost, but higher variability in results.

Spray foam: Use as part of a layered approach. Spray foam provides insulation AND some air sealing, but it won’t seal every gap on its own. Best combined with other methods.

Aerosol sealing: Use when the target is 1.5 ACH50 or below, or when first-test pass certainty matters. The insurance policy for Step 4 and Step 5.

The Layered Approach

The most reliable strategy for Step 4 and Step 5 combines methods:

1. Design phase: Plan your air barrier continuity with your energy advisor
2. Framing: Install air barrier materials at rough-in
3. Pre-drywall: Apply aerosol sealing to close all remaining gaps
4. Test: Mid-construction blower door test to verify before closing up
5. Final: Confirm results at the as-built test

This approach gives you the highest confidence and the lowest risk of failure.

Use our rebate calculator to see how much you stand to gain (or lose) at different Step Code levels.