Testing Air Permeability in a Completed Cladding Envelope

Air permeability testing measures how much uncontrolled air passes through a building envelope when a pressure difference exists between the inside and outside. For a completed cladding system, the test is used to identify gaps at joints, interfaces, penetrations, doors, windows, roofing transitions and service openings before they become a source of energy loss, draughts or moisture problems.

A reliable test is more than placing a fan in a doorway and recording a result. The building must be prepared correctly, the test pressure must match the agreed standard, and the readings must be interpreted alongside the design requirements. On a large commercial project, the test may need to be coordinated with multiple facade zones, plant rooms, risers and internal fire or smoke compartments.

Australian projects also require attention to the National Construction Code, the building’s energy model and the performance requirements set out in the contract. Local weather conditions matter: a high-rise facade in Melbourne may experience strong wind-driven pressure changes, while a warehouse in Brisbane may rely heavily on controlled ventilation and air conditioning during humid summer conditions.

Establish The Required Test Standard

Before testing starts, the project team should define what is being tested and which standard governs the procedure. A whole-building air leakage assessment is different from a curtain wall or window test. For an occupied building, the objective may be to measure overall leakage at a reference pressure. For a facade package, the focus may be the air permeability of curtain walling, rainscreen cladding, glazed screens, windows and their connections.

Australian facade work commonly refers to AS/NZS 4284 for performance testing of building facades, while window and external glazed door requirements may involve AS 2047. International methods such as ISO 9972, EN 12152 or ASTM E783 can also appear in specifications, particularly where the facade system or manufacturer’s data is based on overseas testing. The contract documents should state the applicable method rather than leaving the tester to select one after construction.

The acceptance limit must also be clear. It may be expressed as airflow per square metre of envelope area at a stated pressure, litres per second per square metre, or air changes per hour for a whole-building test. There is no single universal pass value for every building type. A hospital, apartment tower, school and industrial facility have different operational requirements, so the target should be taken from the performance specification, facade design report or approved shop drawings.

Prepare The Building For Measurement

Testing should take place when the relevant enclosure is substantially complete. Cladding panels, flashings, membranes, windows, doors, roof interfaces and permanent seals should be installed, while defects that could distort the result should be recorded rather than concealed. The building must be safe for testing, with loose materials secured and temporary openings controlled.

All intentional openings need to be identified. Mechanical ventilation grilles, exhaust outlets, smoke relief openings, loading doors and combustion air paths may need to be temporarily sealed, depending on the scope of the test. Drains, traps and plumbing fixtures should be checked because open connections can create substantial leakage that is unrelated to the facade workmanship. Fire doors and internal doors also need to be positioned according to the agreed test arrangement.

Weather conditions should be logged, including wind speed, temperature and barometric pressure. Strong winds can make readings unstable, especially on exposed elevations or tall buildings. In Australian cities such as Sydney and Melbourne, testing may need to be scheduled around sudden weather changes rather than simply placed at the end of the construction programme. The test area, internal volume, envelope area and temporary sealing locations should all be documented.

Use Calibrated Fans And Pressure Sensors

A blower door or calibrated fan assembly creates a controlled pressure difference between the building interior and the outside. The fan is usually installed in an external doorway or a specially prepared opening. A flexible panel forms an airtight connection around the fan, while a manometer measures the pressure difference and the fan controller records the volume of air required to maintain that pressure.

For a whole-building test, the fan is commonly operated through a series of pressure steps rather than at one pressure only. The technician records airflow at each step and uses the results to establish the building’s leakage relationship. Testing may be performed under both pressurisation and depressurisation where the selected standard requires it. The final report should state the direction, pressure range, equipment identification, calibration status and environmental conditions.

Large buildings may require several fans operating together. This is common for office towers, shopping centres and apartment developments where one doorway cannot generate enough pressure or where different zones must be tested independently. The internal arrangement matters: open doors can connect zones, while closed fire doors can divide them. A test of the external envelope should not accidentally become a test of unplanned internal compartment leakage.

For a facade-only assessment, a pressure chamber or calibrated test rig may be used instead. This approach can isolate a curtain wall bay, window group or cladding interface and is useful where the whole building is occupied or where the specification requires a system-level verification. The test equipment and pressure range must be suitable for the installed facade and agreed with the consultant and manufacturer.

Locate Leakage Paths During The Test

A numerical result shows how much air is moving, but it does not identify where the envelope is leaking. Once the building is stabilised at a suitable pressure, technicians can inspect the enclosure using smoke pencils, theatrical smoke, anemometers or other approved tracing methods. The airflow may be visible around window corners, panel joints, door thresholds, parapet caps, roof penetrations and service penetrations.

Typical defects include discontinuous air seals behind rainscreen panels, poorly compressed gaskets, missing sealant at mullion junctions, unsealed bracket penetrations and gaps around pipework or cable trays. Curtain wall interfaces with concrete slabs are particularly important because the perimeter fire stopping, spandrel zone and internal air seal must work as a continuous assembly. A visually neat external facade can still contain a significant leakage path behind the cladding.

Infrared cameras can assist with diagnosis when there is a sufficient temperature difference between inside and outside, although thermal images do not measure air leakage directly. They may show cold air paths or areas of disturbed insulation that require further investigation. On a hot Queensland day, the temperature pattern may be different from a cool winter test in Victoria, so the operator should avoid treating every thermal image as definitive evidence.

Leakage locations should be marked on elevation drawings or digital models and classified by severity. A small isolated gap may be repaired locally, while repeated leakage at a system interface may indicate a design coordination or installation issue. The BIM coordination benefits become especially valuable when test findings must be traced to structural edges, brackets, membranes and service zones.

Repair And Retest The Envelope

Remedial work should follow the approved facade details and product installation requirements. Sealant should not be applied over contaminated or unsuitable surfaces, and compressible seals should not be substituted with an unapproved material simply because it closes a visible gap. Repairs may involve replacing damaged gaskets, extending perimeter membranes, sealing fastener penetrations or correcting interfaces between cladding and glazing.

After repairs, the affected zone should be retested. A local diagnostic check can confirm whether the particular defect has been closed, but it does not always prove that the entire facade meets its contractual target. Where the initial result fails significantly, a full repeat test is usually more meaningful than relying only on a series of small spot checks.

The team should control the sequence carefully. If internal linings or ceilings are installed before the first test, important leakage paths may be hidden. Conversely, if membranes are tested before final cladding and flashings are complete, the result may not represent the finished envelope. Test timing should be linked to inspection hold points, allowing access for repair before finishes make the work difficult or destructive.

For residential developments in Australia, practical access is a major consideration. Apartment corridors, car park exhaust systems and shared risers can complicate zone isolation, while residents may already be using entrance doors and balconies. Commercial projects may face similar issues when tenancy fit-outs start before the external envelope has been fully verified.

Record Results For Handover

The final report should identify the building, tested zone, date, weather conditions, test standard, equipment, calibration information and temporary sealing arrangement. It should include measured pressure and airflow values, calculated leakage indicators, the envelope area or internal volume used in calculations, and the specified acceptance criterion. Any departures from the approved method should be explained rather than omitted.

Photographs and marked-up drawings should show significant leakage locations and completed repairs. Product data, approved shop drawings and inspection records can be attached to demonstrate how the facade build-up was intended to perform. Where the project uses a digital coordination model, test observations can be linked to facade zones and interface details for future maintenance.

The results may also support energy compliance and commissioning records. Airtightness affects the performance of heating, ventilation and air-conditioning systems, particularly in buildings operating for long hours. In Perth and Adelaide, where hot, dry conditions can produce heavy cooling demand, uncontrolled infiltration can undermine the energy strategy. In Brisbane, humid outdoor air entering through defects can increase latent cooling loads and contribute to condensation risk in poorly detailed areas.

A completed test should therefore be treated as part of the building envelope quality process, not as an isolated paperwork exercise. An integrated contractor such as Bak Cladding Solutions can coordinate cladding, roofing, glazing, interfaces and handover documentation so that the measured performance reflects the complete external enclosure rather than one product considered in isolation.