Large and multizone buildings cannot always be evaluated with the same straightforward setup used for a small, single-zone property. Professional Large Building Airtightness Testing requires careful boundary definition, sufficient fan capacity and coordinated pressure measurements across different parts of the building. ASTM E3158 provides a standardized method for carrying out this work and calculating the resulting air-leakage rate.
The standard is particularly relevant to commercial buildings, multi-family developments, institutional facilities and other properties containing multiple floors, shafts, mechanical zones or physically separated sections.
This guide explains ASTM E3158 in practical terms, including what it measures, how the building is prepared, which test procedures are available and how the final result should be interpreted.
What Is ASTM E3158?
ASTM E3158 is formally titled Standard Test Method for Measuring the Air Leakage Rate of a Large or Multizone Building. The current active edition is ASTM E3158-24.
The standard establishes a quantitative field-test procedure for measuring air leakage through a constructed building envelope. Calibrated blower doors or equivalent fan equipment create controlled pressure differences between the test area and the exterior. The airflow required to maintain those pressure differences is measured and used to calculate the envelope leakage rate.
In simple terms:
- A tighter envelope requires less fan airflow to maintain the test pressure.
- A leakier envelope requires more airflow.
- The result represents the combined leakage through the defined test boundary.
ASTM E3158 can be applied to an entire large building, a multizone building or an appropriate portion or subsection of a building. It is specifically designed to address pressure relationships that may exist between floors, rooms, corridors, shafts and other connected or separated areas.
What is a multizone building?
A multizone building contains internal areas that may not behave as one freely connected air volume.
Examples may include:
- Apartments separated from corridors
- Floors divided by enclosed stairwells
- Mechanical rooms with dedicated ventilation
- Retail units beneath residential floors
- Hospital or laboratory areas with controlled pressure relationships
- Warehouses connected to offices
- Buildings containing elevator shafts and service risers
The word “zone” in this context does not necessarily refer only to an HVAC zone. It refers to an area whose pressure relationship may need to be considered during the airtightness test.
What Does ASTM E3158 Measure?
ASTM E3158 measures the rate at which air crosses the defined test envelope under a controlled pressure difference.
The test answers a quantitative question:
How much airflow is required to maintain a specified pressure across this building envelope?
It does not directly explain why the leakage exists or identify the exact location of every opening.
The measured leakage may include airflow through:
- Window and curtain-wall connections
- Roof-to-wall transitions
- Expansion and control joints
- Service penetrations
- Loading doors and exterior entrances
- Mechanical louvers and dampers
- Air-barrier transitions
- Cracks or incomplete seals
- Interfaces between different construction assemblies
The standard evaluates the completed enclosure as a system. This is important because individual materials or assemblies may perform well in laboratory testing while transitions, installation sequencing and workmanship create leakage in the constructed building. ASTM distinguishes whole-envelope testing from material and assembly tests that do not capture all these field conditions.
Does ASTM E3158 set a passing airtightness target?
No. ASTM E3158 explains how to perform and calculate the test, but it does not establish one universal leakage limit.
The allowable result must be defined elsewhere, such as in:
- The project specification
- The owner’s project requirements
- An energy-performance standard
- A building code or municipal requirement
- An energy model
- A building-envelope commissioning plan
The testing team must know both the required leakage metric and the reference pressure before the test begins. ASTM E3158 provides a means of assessing compliance with air-leakage limits established by another document.
Why Large Buildings Need a Dedicated Testing Method
A small house can often be treated as one pressure zone. One calibrated fan may be sufficient, interior doors can be opened and pressure can be measured from a limited number of locations.
Large buildings introduce additional variables.
A high-rise may experience different pressures at the ground floor and roof because of wind and stack effect. A corridor may respond differently from the suites around it. An elevator shaft may connect numerous floors. Mechanical dampers, smoke-control systems and exhaust equipment may also influence pressure during the test.
The building may therefore require:
- Several calibrated fans
- Multiple fan installation points
- Pressure monitoring on different floors
- Communication between several testing technicians
- Coordination with the mechanical contractor
- Control of elevators and exterior doors
- Temporary treatment of intentional openings
- Monitoring for airflow between internal zones
ASTM E3158 addresses these complexities by requiring the test team to define the pressure boundary and maintain appropriate relationships between connected subsections during testing. Isolated subsections with separate leakage requirements must be treated as separate test envelopes, while flanking airflow between zones must be monitored.
How Does an ASTM E3158 Test Work?
An ASTM E3158 test begins well before the fans are switched on.
The project documents, building configuration and required compliance target must first be reviewed. The team then develops a test plan identifying the pressure boundary, preparation condition, equipment requirements and measurement procedure.
1. Define the test boundary
The test boundary identifies the physical surfaces through which leakage will be measured.
For a whole-building test, this may include:
- Exterior walls
- Roof assemblies
- Ground-contact floors
- Exterior windows and doors
- Mechanical penetrations
- Interfaces between the enclosure and adjacent structures
For a partial-building test, the boundary may also include floors or interior partitions separating the test zone from untested areas.
The boundary must be clearly defined because it affects building preparation, pressure monitoring and the area used to normalize the result.
A vague or disputed boundary can make the final result difficult to interpret, even when the airflow measurements themselves are technically accurate.
2. Choose the building preparation condition
ASTM E3158 recognizes two distinct preparation approaches.
Building-envelope condition
Under the building-envelope condition, HVAC-related openings are excluded or prepared according to the agreed test plan.
This approach is intended to focus on the constructed enclosure by temporarily addressing intentional mechanical openings that are not meant to represent uncontrolled envelope leakage.
Operational-envelope condition
Under the operational-envelope condition, applicable HVAC-related openings are included.
This configuration evaluates the envelope while accounting for the intentional openings that form part of the selected operational boundary.
The correct condition must be stated in the specification or agreed upon before testing. The two conditions do not represent the same boundary and should not be treated as interchangeable. ASTM notes that window positions and the treatment of HVAC penetrations and other intentional openings can strongly affect the final result.
3. Prepare the building
Building preparation may involve:
- Closing exterior windows and doors
- Opening selected interior doors
- Setting dampers to defined positions
- Shutting down specified mechanical equipment
- Temporarily sealing designated intentional openings
- Confirming the condition of loading doors and roof hatches
- Controlling access during the test
- Reviewing combustion and life-safety considerations
- Recording indoor and outdoor temperatures
- Measuring baseline pressures before fan operation
Every sealed, open or operational component should follow the agreed test plan. Unplanned changes during testing can alter the result.
For example, someone opening an exterior door while readings are being recorded may cause a sudden pressure loss. An overlooked exhaust damper may add airflow that is mistakenly counted as uncontrolled leakage.
4. Install calibrated fans and gauges
One or more calibrated fans are installed in exterior doorways, temporary panels or other suitable openings.
The total fan capacity must be sufficient to reach the project’s required pressure. A large or relatively leaky building may require several fan arrays operating simultaneously.
Differential-pressure gauges measure:
- Indoor-to-outdoor pressure
- Pressure relationships between internal areas
- Fan airflow
- Baseline pressure before and after the test
Outdoor pressure reference tubes must be positioned carefully because wind pressure can differ across various sides of the building.
In a tall building, readings may also be taken at multiple elevations to understand whether the intended pressure is being achieved throughout the test envelope.
5. Pressurize or depressurize the building
During depressurization, fans remove air from the building. Outdoor air then enters through leakage paths.
During pressurization, fans supply air to the building. Indoor air exits through those same paths.
ASTM E3158 allows testing under pressurization, depressurization or both. When both directions are required, the results may be averaged according to the specified procedure. The standard applies to reference-pressure specifications greater than 10 Pa and not greater than 100 Pa.
Testing in both directions can provide a broader view of envelope performance. Differences between pressurization and depressurization results may arise from wind, dampers, flexible seals or other components that respond differently depending on airflow direction.
The Three ASTM E3158 Test Procedures
ASTM E3158 defines three data-collection procedures:
- Multipoint regression
- Repeated single-point testing
- Repeated two-point testing
The appropriate procedure should be established in the test plan rather than selected casually after testing has begun.
Multipoint regression testing
The multipoint method collects airflow measurements across several pressure differences.
As fan speed changes, the technician records the airflow required to maintain each pressure station. The readings are then used to establish the relationship between pressure and leakage airflow.
Conceptually, the data create a rising curve:
- Low pressure produces lower measured airflow.
- Higher pressure produces greater airflow.
- The fitted relationship allows leakage to be calculated at the specified reference pressure.
Because the method uses several pressure points, it provides more information about the building’s airflow-pressure behaviour than a single reading.
Repeated single-point testing
The repeated single-point method takes several measurements around one specified test pressure.
Repeating the measurement helps reduce reliance on one potentially unstable reading. This can be useful where the compliance requirement is based on one defined reference pressure and test conditions allow consistent readings around that point.
The test pressure must still be achieved reliably throughout the relevant boundary.
Repeated two-point testing
The repeated two-point method collects multiple measurements at two selected pressure levels.
It provides more information than a single-point procedure while requiring fewer pressure stations than a complete multipoint regression test.
The project specification and testing conditions should determine whether a multipoint, repeated single-point or repeated two-point procedure is appropriate.
A Simple ASTM E3158 Example
Consider a six-storey multi-family building approaching completion.
The building contains residential suites, corridors, two stairwells, an elevator shaft, a parkade connection and several mechanical systems. Although the building is one structure, its internal areas may not automatically reach the same pressure when the fans operate.
Before testing, the team defines the exterior enclosure as the test boundary. It confirms which mechanical openings will be temporarily sealed and which will remain in the selected operational condition.
Several calibrated fans are installed in exterior door openings. Pressure gauges are placed at different elevations and in selected internal areas.
When the fans depressurize the building, outdoor air begins entering through leakage paths across the enclosure. The fans must remove that incoming air to maintain each test pressure.
Suppose the measured airflow is higher than the project’s allowable leakage rate. The result confirms that the building envelope does not currently meet the specified target.
It does not tell the team that one particular window is responsible.
Separate diagnostic work may then use smoke, infrared thermography or localized investigation to identify likely leakage areas. Repairs can be completed, followed by a retest to measure whether total leakage has been reduced.
This distinction is central to understanding ASTM E3158:
The test measures how much the defined envelope leaks. Diagnostic testing investigates where the leakage occurs.
How Are ASTM E3158 Results Reported?
A complete airtightness result must identify:
- Measured or calculated airflow
- Reference pressure
- Test direction
- Test procedure
- Building preparation condition
- Test-envelope area
- Normalized leakage rate, where required
- Relevant weather and baseline-pressure conditions
An airflow value by itself is incomplete.
For example, a result of 20,000 cubic feet per minute has little meaning unless the report also states the pressure at which that airflow occurred and the size of the tested enclosure.
Airflow at a reference pressure
The report may express airflow in units such as:
- Litres per second
- Cubic metres per second
- Cubic feet per minute
The pressure must be included beside the airflow value.
A notation such as CFM75, for example, refers to cubic feet per minute at a pressure difference of 75 Pa.
Leakage normalized by envelope area
Raw fan airflow tends to increase with building size. A large building normally has more enclosure surface and potentially more leakage paths than a small building.
For this reason, large-building requirements commonly express leakage relative to the test-envelope area.
A normalized result allows the measured building to be compared with its project requirement without treating total airflow alone as the performance metric.
The method used to calculate the envelope area should be confirmed before the test. Different interpretations of below-grade surfaces, shared boundaries, roofs or parkade interfaces can change the normalized result.
Passing and failing
A building passes when the measured result satisfies the leakage limit defined by the applicable project requirement.
Passing ASTM E3158 testing does not mean the building contains no air leaks. ASTM specifically notes that compliance with a specified leakage rate does not prove that every potentially problematic leak has been sealed.
A building may meet its overall target while still containing a concentrated leak near a roof transition, window interface or mechanical penetration.
Such a leak may be important because of its location, even when its airflow contribution is not large enough to cause an overall test failure.
What Can Affect ASTM E3158 Test Accuracy?
Reliable results depend on stable conditions, correct building preparation and sufficient testing equipment.
- Wind and temperature differences: Gusts and stack effect can create unstable pressure across the building, especially in tall structures.
- Building height and internal shafts: Stairwells, elevator shafts and service risers can affect pressure distribution between floors.
- Mechanical-system settings: Open dampers, active exhaust fans or unaccounted-for louvers may alter the measured airflow.
- Fan capacity and equipment setup: The fan system must provide enough airflow to reach the required pressure and operate within its calibrated range.
- Activity during testing: Exterior-door use, elevator movement and ongoing construction can disrupt pressure readings.
Testing may need to be postponed when weather or site conditions prevent stable measurements. The final report should document the building configuration, equipment setup and relevant test conditions.
ASTM E3158 Compared with Related Standards
ASTM maintains several standards related to building airtightness. Their purposes overlap, but they are not interchangeable.
| Standard | Main Purpose | Best Used For |
|---|---|---|
| ASTM E3158 | Measures total air leakage in large or multizone buildings. | Commercial, multi-family, institutional, high-rise and other complex buildings. |
| ASTM E779 | Measures building-envelope leakage using fan pressurization. | Buildings that can be tested as a single pressure zone. |
| ASTM E1827 | Measures airtightness using an orifice blower-door system. | Single-zone buildings tested with blower-door equipment. |
| ASTM E3474 | Measures leakage through one defined test zone within a multizone building. | Individual floors, suites, sections or isolated zones. |
| ASTM E1186 | Helps locate specific air-leakage sites. | Diagnostic investigation using smoke, infrared imaging, fog or similar methods. |
Plan Your Airtightness Test with Shahin Arvandi
ASTM E3158 provides a structured measurement method, but the quality of the result depends on project-specific decisions made before testing.
Large-building airtightness work requires more than sufficient fan airflow. It requires a correctly defined boundary, coordinated building preparation, stable pressure measurements and a reporting method aligned with the project requirement.
For guidance on testing a commercial, multi-family, institutional or other large building, consult Shahin Arvandi, Founder of Monolith Housing Solutions. Shahin is a Certified Air Tester, Certified Thermographer and Senior Energy and Building Science Specialist with more than 15 years of experience in airtightness testing, commissioning and high-performance building design.
Early consultation can help establish the applicable standard, estimate fan-capacity requirements, define site responsibilities and identify potential testing constraints before they affect the construction schedule.
Frequently Asked Questions
Is ASTM E3158 a blower-door test?
ASTM E3158 uses blower doors or equivalent calibrated fan equipment to create controlled pressure differences across a large or multizone building envelope. A large project may require several blower-door systems operating together.
Can ASTM E3158 be used for part of a building?
Yes. The method can apply to large or multizone buildings and appropriate portions or subsections. The test boundary and pressure relationships with adjacent areas must be clearly defined.
Does ASTM E3158 define a passing leakage rate?
No. It provides the method for measuring leakage and assessing compliance with a limit established by another document, such as a project specification or code requirement.
What is the difference between the building-envelope and operational-envelope conditions?
The building-envelope condition excludes applicable HVAC-related openings according to the test plan. The operational-envelope condition includes those openings within the evaluated boundary.
Does the test need both pressurization and depressurization?
Not necessarily. ASTM E3158 permits pressurization, depressurization or both, depending on the specified test procedure.
What pressures are used under ASTM E3158?
The standard applies to air-leakage specifications with a reference pressure greater than 10 Pa and no greater than 100 Pa.
Can ASTM E3158 locate the individual leaks?
No. It quantitatively measures total leakage through the defined envelope. Diagnostic methods such as infrared thermography or smoke testing may be used separately to investigate leakage locations.
Does passing mean that every leak has been sealed?
No. A building can meet the specified overall leakage rate while still containing localized leakage sites that may warrant investigation because of their position or potential effect on comfort and durability.
