Step Code Airtightness and ACH50 Explained

Short answer

Every Part 9 home built under the BC Energy Step Code needs an on-site airtightness (blower-door) test, and Step 3 is the minimum province-wide since May 1, 2023. Airtightness is reported in ACH50, air changes per hour at 50 pascals. The working targets builders use are 2.5 ACH50 for Step 3, 1.5 for Step 4 and 1.0 for Step 5. Under the 2024 BC Building Code the steps are measured on energy performance, so your energy advisor confirms the exact airtightness your model needs. A measured seal brings the house to that number before the test.

What ACH50 means

A blower door depressurizes or pressurizes the house to 50 pascals and measures the airflow needed to hold that pressure. That airflow is CFM50. Divide it into the house volume and you get ACH50: how many times per hour the whole volume of air would leak out at that pressure. Lower is tighter.

Because ACH50 divides by volume, small homes and compact suites have a harder time hitting the same number as a big house with the same quality of work. That is why townhouses and fourplexes miss more often. See multi-family air sealing.

The airtightness targets builders work to

Targets from the Province's Step Code guidance table (Bulletin B19-03). The 2024 BC Building Code expresses the Part 9 steps as energy performance improvements, with measured airtightness feeding the energy model. Confirm your project's number with your energy advisor.
Step	Airtightness target	What it means on site
Step 3	2.5 ACH50	Province-wide minimum for Part 9 since May 1, 2023. A careful crew can hit it by hand.
Step 4	1.5 ACH50	About 40% less leakage than Step 3. This is where hand sealing starts coming up short.
Step 5	1.0 ACH50	Net-zero-ready territory. Takes a deliberate air barrier strategy plus a measured seal on most builds.

The 2024 BC Building Code also added airtightness levels and two more ways of reporting leakage, NLA10 and NLR50, which normalize leakage to the envelope area instead of the volume. Your energy advisor decides which metric the file uses. Whatever the metric, the job on site is the same: take leakage out until the number is where the model needs it.

When the blower door tests happen

The BC Building Code requires the airtightness test at completion. Many builders and some municipalities add a mid-construction test, run once the air barrier is complete and before drywall, when leaks can still be found and fixed. Penticton requires airtightness testing at mid-construction and completion. Some FortisBC programs also require a mid-construction test.

The mid-construction test is the cheapest moment to find out you have a problem. It also lines up with the best moment to seal. Booking the seal around it means you go into the final test already knowing the answer.

Okanagan municipalities at a glance

Checked October 2026 against the sources below. Requirements change; confirm with the authority having jurisdiction before you rely on them.
Municipality	Part 9 requirement	Notes
Kelowna	Step 3	Step 3 required since June 2021. Airtightness test at completion. Check kelowna.ca for any current mid-construction test incentive.
Vernon	Step 3, plus Zero Carbon Step Code EL-1	Step 3 since January 1, 2023 (Building Bylaw 5900, s.15.3). EL-1 is measure-only (Bylaw 5993).
Penticton	Step 3	Mid-construction and completion airtightness tests required (Building Bylaw 2021-21).
Other Okanagan communities	Step 3 provincial minimum	Check with the local building department or regional district before you price the envelope.

Where an air seal fits

Your designer and energy advisor set the airtightness the model needs.
Framing and air barrier details do most of the work. Big holes get sealed by hand.
Mid-construction test (if you run one) gives a baseline.
I seal the house to the target, measured live, and you get an Airtightness Verification Report. How a seal day runs.
Your energy advisor runs the compliance test. Their number goes on the file.

Typical finished results on my seals land between 0.5 and 1.2 ACH50. The best on record is 0.24.

The FortisBC rebate deadline

FortisBC says its New Home Program is close to its budget cap and ends February 28, 2027, paying only on completed homes with an occupancy permit (fortisbc.com, read October 8, 2026). Confirm current terms at fortisbc.com before you count on it. The airtightness test does not end with the program.

For the deeper code walkthrough, the BC Step Code guide (my sister site) covers modelling, steps and timelines.

Sources

Written by Sebastian Motora, owner-operator. Last reviewed October 7, 2026.

Common questions

What ACH50 do I need for Step 4 in BC?

Builders work to 1.5 ACH50 for Step 4, from the Province's Step Code guidance. Under the 2024 BC Building Code the step is set by energy performance, so your energy advisor confirms what your model needs.

Is a mid-construction blower door test required?

Not by the BC Building Code itself, but some municipalities require one (Penticton does). It is the cheapest time to catch a problem, so most builders aiming above Step 3 run one.

What happens if my final test fails?

You do not get the result you need for the file until the leakage comes down and the house is retested. If finishes are not in yet, a seal can usually fix it. Failed blower door test.

Do you do the Step Code test?

No. I am not an energy advisor. Your energy advisor runs the compliance test; I seal the house to the target before they do. How we work together.

Is Step 4 going to be required everywhere?

The Province has set a path to net-zero-energy-ready new construction by 2032. The timing of higher minimum steps can move, so check the current requirement with your municipality when you price a job.

Send me the project.

Plans, target step, stage and timeline. You talk to the owner who runs the seal, usually the same day.

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BC Step Code airtightness and ACH50, explained.