Part 3 Buildings

Large Building
Airtightness Testing

Professional whole-building airtightness testing for mid-rise, commercial, and multi-unit residential projects across BC. ASTM E779-compliant testing with experienced Energy Advisors.

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What Is It

Airtightness Testing for Part 3 Projects

Large building airtightness testing measures how much air moves through a building's envelope under controlled pressure conditions. For Part 3 buildings this is a fundamentally different undertaking than single-family blower door testing.

Where a Part 9 residential test most often requires minimal preparation (relatively speaking) and a single blower door fan, large building testing requires multiple coordinated blower door fans running simultaneously to pressurize or depressurize the full building envelope. Results are reported in accordance with ASTM E779 and are used to verify the airtightness assumptions in the energy model submitted for BC Energy Step Code compliance.

As registered Energy Advisors, Thrive Energy provides the in-field measurement data that sits alongside the engineer's energy model - confirming that the building enclosure performs as designed before occupancy.

Note: For most Part 3 projects, the energy model must be completed by a Professional Engineer. Thrive Energy partners with engineering firms to provide the airtightness testing component that confirms real-world performance matches what the engineer modelled.

~25%

of space heating energy in large buildings is typically lost through air leakage, making airtightness one of the highest-leverage performance levers available.

ASTM E779

Testing standard most commonly used for Part 3 airtightness verification in BC Energy Step Code compliance documentation.

2× Tests

Both depressurization and pressurization tests are completed, with results averaged to demonstrate enclosure performance from both directions.

Who We Work With

Is This Service Right for Your Project?

Large building airtightness testing applies to a range of project types. If your project falls under Part 3 of the BC Building Code and is targeting BC Energy Step Code compliance, you likely need this service.

Multi-Unit Residential

Multi-unit residential buildings over 3 storeys - including purpose-built rental, strata, and mixed-use with residential above grade - where whole-building airtightness verification is required for Step Code compliance.

Builders & Developers

Project teams working with a Professional Engineer on Part 3 compliance documentation who need a certified third party to perform and report on the in-field airtightness test.

Architects & Engineers

Design and engineering teams who need a reliable airtightness testing partner to collect the field data that validates their energy model assumptions and completes the compliance package.

The Process

What to Expect

Part 3 Large building testing requires more coordination and preparation than Part 9 residential testing. Here is what the process looks like from start to finish.

Send Us Your Architectural Drawings

Share your architectural drawings and project details. We'll review building volume, exterior envelope area, number of units, and project schedule to scope the work accurately. Because every large building is different, pricing is project-specific - there's no standard rate list.

Pre-Test Coordination

We work with your team to confirm the building is ready for testing. This includes verifying that HVAC intake and exhaust grilles, relief dampers, and mechanical penetrations have been temporarily sealed. Proper preparation prevents failed tests and costly re-mobilizations.

On-Site Testing

After proper site-preparation is confirmed, multiple calibrated blower door fans are installed at exterior openings and run simultaneously. We complete both depressurization and pressurization tests. For high-rise configurations, guarded floor-by-floor testing is used to obtain accurate zone-level results. Environmental conditions, wind speed, temperature, and stack effect, are monitored throughout.

Results & Reporting

Results are reported in Air Changes per Hour (ACH) and Normalized Air Leakage Rate (NLR). We provide a clear summary document that your engineering team can reference in the Step Code compliance package submitted to the Authority Having Jurisdiction.

Key Differences

How Large Building Testing Differs from Residential

If you've worked with Thrive Energy on Part 9 residential projects, it's worth understanding how this scope differs, both technically and logistically.

Multiple Fans, One Test

Residential testing most often uses a single blower door fan. Large building testing requires multiple coordinated fans running simultaneously to create and maintain the required pressure differential across the entire building envelope.

Engineer & Advisor Roles Are Separate

For Part 3, the energy model is prepared by a Professional Engineer (there are a few exceptions to this). Thrive Energy provides the independent airtightness measurement. The two deliverables complement each other in the final compliance submission.

More Preparation Required

The building must be properly prepared before testing begins. Mechanical openings need to be sealed, the building must be enclosed, and scheduling must account for weather conditions. Coordination starts well before the test date.

Weather & Conditions Matter More

Stack effect, wind speed, and temperature differentials have a greater influence on results in large buildings. Testing is scheduled during low-wind periods. If conditions deteriorate, we may need to reschedule to protect result integrity.

Different Metrics

Residential testing reports ACH50. Large building results are typically reported as Normalized Leakage Rate (NLR) in L/s·m² at 75 Pa, which accounts for the building's volume-to-surface-area ratio.

Project-Specific Pricing

Large building testing is scoped individually based on building size, configuration, number of fans required, and site conditions. There's no standard rate. Contact us with your architectural drawings for a job-specific estimate.

BC Energy Step Code

Where Airtightness Testing Fits in Step Code Compliance

As Part 3 Energy Step Code requirements roll out across BC municipalities, airtightness testing is now a standard compliance requirement for mid-rise and commercial construction, not just high-performance or net-zero projects.

Airtightness testing validates the enclosure performance assumed in the engineer's energy model
Test results are documented in the final compliance checklist submitted to the Authority Having Jurisdiction
Achieving results that align with modelled targets confirms the building performs as designed
Testing is a construction and occupancy-stage verification - it happens in the field, not on paper
Energy Advisors are well-positioned to provide this testing, often more cost-effectively than engineering firms

Pricing

Every Project Gets a Project-Specific Estimate

Large building airtightness testing is scoped based on your specific project — building size, configuration, height, number of fans required, and location all factor into the cost. Send us your architectural drawings and we'll come back to you with a clear, itemized estimate with no surprises.

Send Your Drawings for a Quote

Quick turnaround. We review your drawings and respond with a scoped estimate, typically within 1 business day.

From the Thrive Energy Blog

Large Building Airtightness Testing for Part 3 Buildings: What Builders Need to Know

Read the Full Guide →

Common Questions

FAQ

Questions we hear regularly from builders and project teams working through Part 3 compliance.

Do I need an energy advisor or an engineer for large building airtightness testing?

For most Part 3 projects in BC, the energy model must be completed by a Professional Engineer. However, airtightness testing, the in-field measurement that validates that model, is a service Energy Advisors are well-positioned to provide, and often more cost-effectively than engineering firms. Many project teams work with both: an engineer for the model and compliance documentation, and an Energy Advisor like Thrive Energy for the field testing.

How many blower door fans are needed?

The number of fans depends on the size and configuration of the building. Testing is performed with the building treated as a single pressure zone where possible, which requires enough fan capacity to achieve the required pressure differential across the full envelope. Larger buildings, or those with multiple pressure zones, require more fans and more coordination on site. We determine this during scoping once we've reviewed your drawings.

What standard is used for large building airtightness testing in BC?

Most large building airtightness testing in BC is performed in accordance with ASTM E779 - the standard method for determining air leakage rate by fan pressurization. Other standards may apply depending on building type and program requirements. We confirm the applicable standard during scoping.

When should testing be scheduled during construction?

Airtightness testing is a construction and occupancy-stage verification activity. It occurs once the building envelope is complete and all exterior penetrations are in place, but before occupancy. Testing should be scheduled during periods of low wind and stable temperatures to ensure reliable data.

What if the building doesn't meet the airtightness target?

If results fall short of the modelled target, we work with your team to identify likely leakage sources. We can coordinate diagnostic testing, including thermal imaging, to help locate problem areas.

How much does large building airtightness testing cost?

Pricing is project-specific and depends on building size, height, configuration, and location. There's really no standard rate for large building testing. It needs to be scoped individually. Send us your architectural drawings and we'll provide a clear, itemized estimate. We aim to respond within one business day.

Large BuildingAirtightness Testing