Every building envelope has gaps. Some are visible around penetrations, joints, and service openings. Others are hidden behind drywall or at the points where different materials meet. Airtightness measures how much conditioned air escapes, and how much outdoor air enters, through these unintended openings — a key detail an energy advisor looks at when assessing how the building envelope affects energy performance, comfort, and moisture control.
The standard metric for houses and Part 9 residential projects in Canada is ACH50: air changes per hour at 50 Pascals of pressure. A home at 3.0 ACH50 exchanges a volume of air equivalent to its interior space three times per hour under that test pressure. For larger buildings, including MURBs and commercial projects, normalized metrics like NLA (cm² per m² of envelope) or airflow per unit envelope area at 75 Pa (L/s/m²) are used instead, because in a large building the volume-to-envelope ratio makes ACH50 misleading.
Why does this matter beyond energy? In cold climates like Toronto, air leaking outward carries moisture into assemblies where it can condense on cold surfaces, increasing the risk of mould and material degradation. In coastal BC, rain exposure and limited drying capacity are among the major envelope risks, though airtightness remains equally important for ventilation control and comfort. A tight envelope paired with properly designed mechanical ventilation, the “build tight, ventilate right” principle, addresses energy, durability, and comfort simultaneously.
How tightly you need to build, and whether you must prove it with a test, depends on your province, municipality, and building type. The sections that follow map out the specific triggers, targets, and compliance paths across jurisdictions.
| Standard / Jurisdiction | Applies To | Testing Requirement | Main Point |
| NBC 2020 | Part 9 homes / small buildings | Not directly mandatory by NBC alone | Model code; provinces decide adoption and enforcement. |
| NECB 2020 | Larger / Part 3 buildings | Path-dependent | Uses larger-building energy compliance methods; airtightness testing may be used for compliance. |
| BC Energy Step Code | BC Part 9 projects where Step Code applies | Yes | Airtightness is verified through testing; metrics may include ACH50, NLA10, and NLR50. |
| Vancouver Building By-law | Vancouver projects | Project-dependent | Vancouver has its own bylaw pathway and may exceed provincial minimums. |
| Ontario OBC / SB-12 | Ontario Part 9 residential | Conditional | No universal testing; blower door test is required when better-than-default airtightness is claimed. |
| Toronto Green Standard | Applicable Toronto developments | Required for certain higher-tier paths | Applies through development approvals, especially larger/multizone buildings. |
| EnerGuide / ENERGY STAR | Voluntary or program-based homes | Yes, if pursuing the program | Useful for labelling and performance documentation, but not a full replacement for AHJ submissions. |
| Passive House | Voluntary high-performance projects | Yes | Benchmark target is much stricter than typical code compliance. |
National Building Code Requirements and the Tiered Framework
Canada’s National Building Code (NBC) is a model code, not a law. Each province decides whether and how to adopt it, so the airtightness requirements on any project are shaped by provincial legislation, not the NBC text alone.
For Part 9 residential buildings, the NBC 2020 introduced a five-tier energy performance framework. Tier 1 represents baseline practice; Tier 5 is generally associated with net-zero energy ready performance, though in practice the outcome depends on jurisdiction, modelling assumptions, and the compliance path chosen. The NBC does not assign a mandatory ACH50 number at each tier. Instead, tiers define overall energy performance levels, and airtightness becomes a practical necessity as targets rise. Reaching Tier 4 or 5 without a well-sealed, tested envelope is rarely achievable in real construction, but that is a practical constraint, not always a direct legal requirement from the NBC alone.
Part 3 buildings follow a separate path under the National Energy Code for Buildings (NECB), which has its own four-tier structure and introduces whole-building airtightness testing as a compliance option with different metrics and verification methods.
British Columbia’s Energy Step Code has mapped its performance levels to national tier equivalents and uses explicit airtightness metrics within its compliance system. Ontario’s OBC and Supplementary Standard SB-12 reflect the national direction toward higher performance but use their own compliance structure rather than adopting the NBC tier model directly. In both cases, the trigger that makes a blower door test required on your project is set at the provincial or municipal level.
Provincial Standards: Ontario vs. British Columbia
For builders working in Ontario and British Columbia — particularly in Toronto and Vancouver — the key contrast is in how compliance verification works: BC’s Step Code mandates testing as proof of airtightness, while Ontario’s SB-12 makes testing conditional upon claiming above-default performance. Where testing is guaranteed, sealing details tend to be embedded in the construction sequence; whereas in Ontario, airtightness quality control depends more heavily on the builder’s own process unless testing is triggered.
British Columbia: Step Code and Tested Compliance
BC’s Energy Step Code creates a tiered compliance framework where airtightness performance is directly linked to compliance level. Projects using the Step Code must demonstrate airtightness through testing. The Step Code uses various metrics — ACH50, NLA10, and NLR50 — with specific thresholds depending on building type, applicable level (AL-1 to AL-4), and the local authority’s adopted step. For Part 9 residential projects where Step Code compliance applies, there is no equivalent prescriptive-only route for claiming Step Code airtightness compliance. Municipalities can require higher steps than the provincial baseline. For Part 3 buildings, whole-building testing, and in some cases targeted or suite-level testing, is increasingly expected at higher compliance levels as a practical means of verifying performance assumptions.
Ontario: SB-12 and the Default-or-Test Structure
Ontario’s SB-12 offers compliance via prescriptive or performance paths. The prescriptive path specifies air barrier details but does not mandate blower door testing. The performance path, using HOT2000 modelling, allows builders to claim airtightness better than the default assumptions (which vary by building type and project configuration). If a builder claims better-than-default airtightness, a blower door test becomes mandatory for verification.
The Toronto Green Standard (TGS) acts as a municipal overlay applied through the development approval process. Tier 2 and above require verified airtightness performance for applicable development types, particularly larger and multizone buildings. Passive House certification is recognized as an alternative compliance pathway for certain TGS performance requirements.
Airtightness Metrics: ACH50, NLA10, and NLR50 Explained
In low-rise housing and most code-compliance discussions, three metrics appear most often, each expressing the same physical reality — air moving through unintended openings — in a different way. ACH50 divides measured airflow at 50 Pa by the interior volume of the building, giving a rate that is intuitive for smaller buildings. It remains the most familiar metric for houses, though BC Step Code reporting also relies on NLA10 and NLR50 alongside it. Its limitation is volume-dependence: a tall, narrow building can appear tighter than a low, spread-out one with identical envelope quality.
NLA10 expresses leakage relative to envelope surface area at a reference pressure of 10 Pa. Because it references enclosure area rather than volume, it is better suited to comparing buildings of different shapes and sizes. BC Step Code uses NLA10 as part of its airtightness level framework.
NLR50 reports airflow per unit of envelope area at 50 Pa. It appears in BC Step Code metrics, newer code discussions, and larger-building testing contexts where results need to be compared on equal footing regardless of building size.
The same test data can often be converted into these metrics, provided the required volume and envelope-area inputs are measured and the test standard supports the calculation. The choice of which to report is dictated by the applicable code path, not by tester preference.
Compliance Documentation and Quality Assurance
Demonstrating airtightness compliance requires a documented chain of evidence from design through construction to final testing. Where testing is required, the blower door test report forms the core submission, commonly including measured airflow rates, calculated ACH50, NLA10, NLR50, or other normalized leakage values, test conditions, building volume and envelope area inputs, and equipment details—though the specific fields required vary by test standard and AHJ.
Testing credentials depend on the compliance pathway. For Part 9 homes under EnerGuide or ENERGY STAR for New Homes, an NRCan-registered Energy Advisor must conduct the evaluation. For code compliance outside these programs, the credential requirement varies by jurisdiction and building type; large or multizone buildings typically require a qualified testing agency experienced in whole-building protocols rather than a residential energy advisor.
In BC Part 9 projects subject to Energy Step Code compliance, the final airtightness result is commonly part of the as-built energy compliance package submitted before occupancy or permit closeout. In Ontario under SB-12, no blower door test is required on the prescriptive path unless airtightness credit or better-than-default leakage is being used for compliance, in which case test results must be available for verification and may be submitted to the AHJ.
Quality assurance during construction involves distinct layers: where applicable, required final post-construction testing; recommended mid-construction blower door tests to identify defects before concealment; visual inspections at critical junctions; and program-specific third-party verification where required. Some BC municipalities explicitly recommend mid-construction testing alongside the mandatory final test to allow corrections before drywall.
EnerGuide and ENERGY STAR frameworks provide standardized reporting templates and audit procedures that can reduce duplicate effort when aligned early with code compliance requirements. However, they do not automatically replace code-specific or AHJ submissions, which may have separate forms and deadlines.
Conclusion
Building airtightness in Canada has moved from optional best practice toward a code-driven, tested, and documented performance requirement. Whether a project falls under BC’s Energy Step Code — where applicable Part 9 projects must demonstrate airtightness through testing — or Ontario’s SB-12, where testing is triggered by above-default performance claims, the direction is consistent: tighter envelopes, verified results, and documented proof.
For builders and designers, the practical takeaway is straightforward. Know your jurisdiction’s trigger for mandatory testing. Confirm the required metric early — ACH50, NLA10, or NLR50 — based on the applicable code path. Integrate air barrier detailing into the construction sequence rather than treating it as a last-minute fix. And align your documentation strategy — whether through EnerGuide, ENERGY STAR, or direct AHJ submission — before construction begins, not after the final test.
The “build tight, ventilate right” principle remains the foundation: a well-sealed envelope paired with properly designed mechanical ventilation delivers energy performance, durability, and occupant comfort simultaneously. As provincial codes and municipal standards continue moving toward higher-performance tiers, early investment in airtightness design and quality assurance is a reliable path to compliance without costly rework.
