Air Sealing for Step Code 4 and 5: The Method That Actually Works
Key takeaway: Aerosol-based sealing (AeroBarrier) is the most reliable method for hitting 1.5 ACH50 and below. Typical results: 0.5 to 1.5 ACH50 with real-time verification. Traditional methods top out around 2.0 to 2.5 ACH50 in most builds.
Step 4 requires 1.5 ACH50. Step 5 requires 1.0. At those targets, the air sealing method you choose is the difference between passing and failing.
The Results Gap
| Method | Typical ACH50 Result | Reliable at Step 4? |
|---|---|---|
| Caulking and sealant | 2.0 to 3.5 | No |
| Taping systems | 1.5 to 2.5 | Sometimes |
| Spray foam (targeted) | 1.5 to 2.0 | Sometimes |
| Aerosol sealing | 0.5 to 1.5 | Yes |
Manual methods depend on perfect execution at every joint, penetration, and transition. One missed bottom plate, one unsealed electrical box, and you are back above 2.0 ACH50. Aerosol sealing finds and fills those gaps automatically under pressure.
Why Aerosol Sealing Wins at Step 4 and 5
AeroBarrier is a computer-controlled process. The building is pressurized to 50 Pa and a water-based acrylic sealant is distributed as an aerosol mist. The pressurized air carries sealant particles to every leak, where they accumulate and seal gaps up to half an inch.
What makes it different:
- Real-time monitoring. The system tracks ACH50 throughout the process. You know your result before the energy advisor arrives.
- Precision targeting. Set a target of 1.5 ACH50 (or 1.0, or 0.8) and the system stops when it reaches it.
- Consistency. Results do not depend on trade quality or weather conditions. The physics of pressurized air does the work.
- Speed. 2 to 4 hours for the sealing process. Half a day total including setup.
Typical cost: $2,000 to $4,500 depending on home size, target ACH, and starting airtightness.
Traditional Methods: Where They Fit
Manual air sealing methods are the foundation of every good air barrier strategy. But they have limits at Step 4 targets.
Caulking and Acoustical Sealant
The traditional workhorse for Step 2 and Step 3. Acoustical sealant at plate connections, silicone at window openings, sealant at penetrations.
- Cost: $500 to $1,500 in materials
- Results: 2.0 to 3.5 ACH50
- At Step 4: Rarely sufficient as a primary strategy
Taping Systems
Purpose-built construction tapes at air barrier joints, sheathing seams, and window flanges. Products from Siga, Pro Clima, and 3M.
- Cost: $1,000 to $3,000 in materials plus 1 to 3 days labour
- Results: 1.5 to 2.5 ACH50
- At Step 4: Possible but requires near-perfect execution
Spray Foam
Closed-cell spray foam at rim joists, penetrations, and complex geometry. Doubles as insulation and air barrier.
- Cost: $2,000 to $5,000 targeted; $15,000 to $25,000 full cavity
- Results: 1.0 to 2.0 ACH50 (full cavity)
- At Step 4: Good at specific locations but too expensive as a whole-house strategy
Side-by-Side Comparison
| Factor | Caulking | Taping | Spray Foam | Aerosol Sealing |
|---|---|---|---|---|
| Typical ACH50 | 2.0 - 3.5 | 1.5 - 2.5 | 1.0 - 2.0 | 0.5 - 1.5 |
| Cost | $500 - $1,500 | $1,000 - $3,000 | $2,000 - $25,000 | $2,000 - $4,500 |
| Time on site | Throughout build | 1 - 3 days | 1 - 2 days | 3 - 6 hours |
| Reliability at Step 4 | Poor | Moderate | Good | Excellent |
| Reliability at Step 5 | Not viable | Difficult | Good | Excellent |
| Workmanship dependence | Very high | High | Moderate | Low |
| Real-time verification | No | No | No | Yes |
The Layered Approach: How Most Builders Hit Step 4
The most cost-effective path to 1.5 ACH50 is a layered strategy:
Layer 1: Manual sealing during framing. Acoustical sealant at all plate connections, sealed electrical boxes, taped vapour barrier seams. Gets you to roughly 2.0 to 2.5 ACH50.
Layer 2: Targeted sealing at high-risk areas. Spray foam at rim joists, canned foam at window rough openings, tape at sheathing joints. Tightens to roughly 1.5 to 2.0 ACH50.
Layer 3: Aerosol sealing to hit the target. AeroBarrier closes the gap from wherever you are to your target number. If your mid-construction test shows 1.8 ACH50, aerosol sealing closes that to 1.5 in a few hours with a verified result.
Choosing Your Approach
Step 3 (2.5 ACH50): Manual methods are usually sufficient with experienced trades. Budget for a mid-construction blower door test as insurance.
Step 4 (1.5 ACH50): Plan the layered strategy. Budget for aerosol sealing as a standard line item. The cost ($2,000 to $4,500) is far less than failing and losing $15,000 in FortisBC rebates.
Step 5 (1.0 ACH50): Aerosol sealing is not optional. Even the best manual air sealing rarely achieves sub-1.0 ACH50 consistently.
For more on hitting your specific ACH target or calculating your rebate potential, see our other builder resources.