Determination of air permeability of curtain walls is a laboratory and field performance test that quantifies the rate of air leakage through facade systems under standardized pressure differentials. Governed by standards such as GB/T 15227, ASTM E283 and EN 12153, the test establishes air-tightness classifications, supports building energy compliance and validates the quality of both curtain wall products and their installation. This article explains the testing principle, specimen requirements, measured parameters, procedures and practical applications of curtain wall air infiltration measurement.
Technical Overview
Air permeability, also referred to as air tightness, describes the ability of a curtain wall to resist uncontrolled air passage through its fixed joints, glazing gaskets, panel connections and operable elements when a pressure differential exists between the exterior and interior. This differential is generated in service by wind action, stack effect and mechanical ventilation, and excessive air leakage leads to increased heating and cooling loads, condensation risk, dust and noise ingress, and degraded acoustic performance of the building envelope.
Determination of air permeability quantifies the volumetric airflow passing through a representative curtain wall specimen at specified static pressure differentials. The specimen is mounted and perimeter-sealed onto a pressure chamber, a controlled pressure difference is established with a variable-speed fan, and the airflow required to maintain each pressure level is measured with calibrated flow meters. Extraneous leakage through the chamber and sealing arrangement is determined by a blank calibration and subtracted, and the net result is corrected to standard air density and expressed per unit area of the wall or per unit length of opening joint. The measured value is then compared with class boundaries defined by the applicable standard to assign an air permeability grade.
- GB/T 15227 — test methods for air permeability, watertightness and wind load resistance performance of curtain walls
- GB/T 21086 — classification of building curtain wall performance
- ASTM E283 — laboratory determination of air leakage through exterior windows, curtain walls and doors
- ASTM E783 — field measurement of air leakage through installed curtain walls and exterior doors
- EN 12153 — curtain walling, air permeability, test method
- EN 12152 and EN 13830 — classification requirements and product standard for curtain walling
Testing Samples
Laboratory Curtain Wall Specimens
Laboratory testing is performed on a full-size representative mock-up, typically at least one story high and one structural bay wide. The specimen must incorporate all typical construction details, including vertical and horizontal joints, fixed glazing with production gaskets, any operable vents or windows, spandrel panels, anchorages and perimeter flashings, assembled and glazed exactly as they would be on the actual building. Including a corner or transition detail is recommended when such details exist in the project, since discontinuities at corners are a frequent source of leakage.
Field Test Specimens
For on-site verification, a completed area of the installed curtain wall is isolated using a temporary test chamber or a blank-off panel sealed to the interior face of the facade. The selected area should be representative of the installation, contain all typical joints and operable elements, and be free of temporary seals other than those required to isolate the test zone. Field specimens are commonly used for construction quality acceptance and diagnostic investigations.
Component and Sub-assembly Specimens
During product development or system certification, smaller sub-assemblies such as operable sashes, unitized panel joints, gasket systems or pressure-equalized cavity details may be tested individually. These component-level tests help identify leakage paths and optimize seal design before full-scale mock-up verification is carried out by an accredited third-party laboratory.
Testing Items
The determination of air permeability typically covers the following measured and derived parameters:
- Air infiltration rate under positive pressure differential across the specimen
- Air exfiltration rate under negative pressure differential across the specimen
- Air leakage per unit area of curtain wall, expressed in cubic meters per square meter per hour
- Air leakage per unit length of openable joint, where operable elements are present
- Extraneous leakage calibration of the chamber and perimeter sealing
- Density-corrected airflow referred to standard atmospheric conditions
- Air permeability classification grade according to the referenced standard
Testing Methods
Chamber-Based Method per GB/T 15227
The specimen is mounted and sealed onto the face of a pressure chamber. After verifying specimen condition and instrument calibration, extraneous leakage is measured using a blank panel. A stepped pressurization sequence covering the range required for classification, starting from the 10 Pa reference level, is applied under both positive and negative pressure. At each stabilized step, the supply or exhaust airflow is recorded, corrected for air density, and reduced by the extraneous leakage. Classification is then assigned against the grade boundaries of GB/T 21086, in which the highest grade corresponds to air permeability not exceeding approximately 0.5 cubic meters per square meter per hour at the 10 Pa reference pressure.
Laboratory Method per ASTM E283
In the ASTM E283 procedure, the specimen is sealed against the wall of a chamber and tested at one or more specified pressure differentials, commonly 75 Pa or 300 Pa for curtain wall projects. The airflow required to maintain each pressure difference is measured with a calibrated flow-measuring device, converted to standard conditions, and reported as leakage per unit area or per unit crack length. This method is widely specified for project mock-up testing and product qualification programs.
European Method per EN 12153
The EN 12153 test method applies a sequence of increasing pressure differentials, typically up to 600 Pa, with airflow measured at each stabilized level under positive and, where required, negative pressure. The resulting leakage-versus-pressure characteristic is compared with the class boundary curves defined in EN 12152, and the curtain wall is assigned the highest class for which all measured values remain within the boundary. This result feeds directly into conformity assessment under EN 13830.
Field Measurement per ASTM E783
For installed curtain walls, a test chamber is sealed to the interior face of a representative area and leakage is measured at specified pressure differentials in the same manner as the laboratory method. Total measured flow is separated into chamber leakage and specimen leakage so that the on-site performance of the actual installation can be evaluated. Field tests are frequently combined with water penetration testing to give a comprehensive picture of envelope quality.
Instrumentation and Data Correction
Key equipment includes a variable-speed pressurization fan, calibrated flow measurement devices such as nozzle banks or laminar flow elements, differential pressure transducers, and instruments for recording air temperature and barometric pressure. All measured airflows are corrected to the standard reference density of the applicable standard, and reporting includes test pressures, net leakage values, specimen dimensions, calculation basis and the assigned classification.
Applications
Air permeability determination serves multiple purposes across the life cycle of a curtain wall project, from system development through construction acceptance:
- Verification of air tightness classification for curtain wall system certification and product conformity marking
- Compliance demonstration for building energy codes and envelope performance requirements
- Input data for HVAC load calculations and whole-building energy simulation
- Supporting documentation for green building certification schemes
- Construction quality acceptance of installed facades in accordance with GB 50210 and project specifications
- Diagnostic and forensic investigation of leakage, condensation and energy performance problems
- Research and development of gaskets, sealant joints and pressure-equalized facade designs
FAQ
What pressure differential is used for curtain wall air permeability testing?
The pressure levels depend on the referenced standard. GB/T 15227 uses stepped pressurization referenced to a 10 Pa classification level, ASTM E283 is typically performed at 75 Pa or 300 Pa as specified for the project, and EN 12153 evaluates leakage over a pressure sequence generally extending up to 600 Pa.
How are the test results expressed?
Net air leakage after subtraction of extraneous leakage and density correction is reported as a volumetric flow per unit area of curtain wall, or per unit length of openable joint where applicable. The result is then compared with the class boundaries of the governing standard to assign a grade.
What is the difference between laboratory and field testing?
Laboratory testing on a mock-up evaluates the inherent performance of the curtain wall system as designed and fabricated, while field testing verifies the workmanship and installation quality of the completed facade on the building. Both approaches use the same fundamental pressure-chamber principle, but field tests require isolation of the test area and careful separation of chamber leakage from specimen leakage.
What are the common causes of excessive air leakage?
Frequent contributors include poorly compressed or discontinuous gaskets, deficient corner joints, improperly engaged glazing wedges, gaps in sealant application, deformed frames and insufficient compression of operable hardware. Because most leakage occurs at joints and interfaces rather than through the panels themselves, specimen preparation and installation quality have a decisive influence on results.
Can air permeability testing be combined with other curtain wall tests?
Yes. Under GB/T 15227, air permeability, watertightness and wind load resistance are typically performed in sequence on the same mock-up, and ASTM E283 is commonly scheduled alongside water penetration and structural tests within a comprehensive pre-conformance or project mock-up test program.