Testing Methods

Air permeability testing quantifies airflow resistance through building materials under controlled pressure differentials. These standardized test methods provide essential data for moisture transport modeling, energy analysis, and building envelope design.

ASTM E2178: Air Permeability of Building Materials

ASTM E2178 establishes the laboratory procedure for measuring air permeability of porous building materials as an intrinsic material property independent of specimen thickness.

Test Principle

The method determines air permeability (ka) by measuring steady-state airflow through a material specimen under known pressure differential:

ka = (μ × q × L) / (A × ΔP)

Where:

• ka = air permeability coefficient (m²)
• μ = dynamic viscosity of air (Pa·s)
• q = volumetric airflow rate (m³/s)
• L = specimen thickness (m)
• A = specimen area (m²)
• ΔP = pressure differential (Pa)

Specimen Requirements

Geometry:

• Minimum specimen diameter: 100 mm (4 in)
• Preferred specimen thickness: 13-50 mm (0.5-2 in)
• Maximum thickness: limited by equipment capacity
• Edge sealing: required to prevent bypass leakage

Conditioning:

• Temperature: 23°C ± 2°C (73°F ± 4°F)
• Relative humidity: 50% ± 5%
• Equilibration time: minimum 24 hours
• Moisture content: record at test initiation

Test Apparatus Components

Measurement Procedure

Pressure differential selection:

• Test at minimum three pressures
• Range: 10-200 Pa typical
• Points distributed logarithmically
• Avoid pressure-induced material deformation

Data collection sequence:

1. Install and seal specimen in chamber
2. Apply lowest pressure differential
3. Allow flow stabilization (30-60 seconds)
4. Record steady-state flow and pressure
5. Repeat for increasing pressure levels
6. Verify repeatability with descending pressures

Flow regime verification: Calculate Reynolds number (Re) for each test point:

Re = (ρ × v × L) / μ

For Darcy flow (laminar): Re < 10 For turbulent flow: Re > 100 Transition region: 10 < Re < 100

Data Analysis

Linear regression: Plot flow velocity versus pressure gradient. For laminar flow, the relationship is linear:

v = (ka / μ) × (ΔP / L)

Slope yields ka/μ ratio. Calculate ka using standard air viscosity at test temperature.

Permeance calculation: Air permeance (C) incorporates specimen thickness:

C = ka / L (units: m³/(Pa·s·m²) or m/s)

Convert to I-P units: m/s × 2.96×10⁷ = perms at 75°F

ASTM E283: Air Leakage Through Exterior Windows, Doors, and Curtain Walls

ASTM E283 measures air leakage rates through assembled building components under static pressure differentials, representing installed performance.

Test Configuration

Chamber setup:

• Component mounted in rigid test frame
• All edges sealed to frame
• Pressure chamber: positive or negative mode
• Metering chamber for flow measurement

Pressure application:

• Standard test pressure: 75 Pa (1.57 psf)
• Alternative pressures: 150, 300 Pa for high-performance applications
• Minimum stabilization time: 10 seconds
• Test duration: sufficient for stable readings

Air Leakage Measurement

Flow rate determination: Measure volumetric airflow required to maintain test pressure:

Q = volumetric leakage rate (cfm or L/s)

Normalization methods:

Performance Classification

AAMA/WDMA/CSA 101/I.S.2/A440:

Field Testing Methods

ASTM E1186: Air Leakage of Building Envelopes

Measures installed air leakage characteristics using pressurization and depressurization techniques.

Equipment requirements:

• Blower door assembly with calibrated fan
• Digital pressure gauge (±1 Pa resolution)
• Temperature measurement devices
• Data acquisition system

Test protocol:

1. Seal intentional openings (HVAC registers, exhaust fans)
2. Establish baseline pressure difference
3. Operate fan at multiple speeds
4. Measure building pressure and flow at each point
5. Test both pressurization and depressurization
6. Average results for final leakage curve

Data presentation: Flow coefficient and pressure exponent from power law:

Q = C × ΔPⁿ

Where:

• Q = airflow rate (m³/h or cfm)
• C = flow coefficient
• ΔP = pressure difference (Pa)
• n = flow exponent (0.5-1.0, typically 0.65)

ASTM E779: Small Chamber Method

Portable chamber technique for isolated component testing in field conditions.

Chamber specifications:

• Volume: 0.1-1.0 m³ typical
• Construction: rigid frame with flexible membrane
• Seal interface: adhesive or mechanical clamp
• Pressure capacity: up to 300 Pa

Applications:

• Window and door leakage
• Penetration sealing effectiveness
• Material joint performance
• Repair verification testing

Specialized Test Methods

ASTM E1677: Heat-Air-Moisture Transport Properties

Dynamic testing under combined thermal and moisture gradients using guarded hot box apparatus.

Measurement capabilities:

• Air permeability under thermal stress
• Temperature-dependent permeance
• Coupled heat and moisture transport
• Convective loop formation detection

ISO 9972: Air Permeability of Buildings

International standard for whole-building airtightness testing with normalized reporting.

Key metrics:

• Air change rate at 50 Pa (ACH₅₀)
• Equivalent leakage area (ELA)
• Normalized leakage (NL)
• Specific leakage rate (SLR)

Instrumentation and Calibration

Differential Pressure Measurement

Micromanometer specifications:

• Resolution: 0.1 Pa minimum
• Accuracy: ±1% of reading or ±1 Pa
• Range: 0-500 Pa for material testing
• Temperature compensation: automatic
• Zero drift: <0.5 Pa per month

Calibration requirements:

• Frequency: annual minimum
• Reference standard: NIST-traceable
• Multiple points across operating range
• Documentation of calibration coefficients

Flow Measurement Devices

Environmental Monitoring

Required measurements:

• Ambient temperature: ±0.5°C accuracy
• Barometric pressure: ±50 Pa accuracy
• Relative humidity: ±3% accuracy
• Wind speed (field tests): ±0.5 m/s

Data correction factors: Normalize flow measurements to standard conditions (20°C, 101.325 kPa):

Qstd = Qmeas × (Pstd/Pmeas) × (Tmeas/Tstd)

Data Interpretation and Reporting

Uncertainty Analysis

Primary error sources:

Combined uncertainty: Calculate using root-sum-square method:

U = √(u₁² + u₂² + … + uₙ²)

Report results with 95% confidence interval.

Statistical Analysis

Minimum specimen count:

• Homogeneous materials: 3 specimens
• Variable materials: 5-10 specimens
• Field verification: 3 replicates minimum

Reporting parameters:

• Mean permeability or permeance
• Standard deviation
• Coefficient of variation
• Minimum and maximum values
• Number of specimens tested

Quality Control Checks

Test validity criteria:

• Flow regime verification (laminar assumption)
• Linear regression R² > 0.95 for Darcy flow
• Repeatability within ±10% between runs
• Hysteresis < 5% between increasing/decreasing pressure
• Zero-pressure flow reading < 1% of lowest test flow

Reference material testing:

• Periodic testing of standard materials
• Control charts for equipment performance
• Interlaboratory comparison programs
• NIST traceable reference specimens

Practical Considerations

Material-Specific Challenges

Fibrous insulation:

• Compression sensitivity during mounting
• Edge sealing without material distortion
• Anisotropic permeability (directional testing)
• Density variation effects

Membranes and barriers:

• Pinholes and manufacturing defects
• Installation damage simulation
• Temperature-dependent properties
• Aging and degradation assessment

Composite assemblies:

• Interface resistance identification
• Layer-by-layer testing for model validation
• Joint and penetration effects
• Thermal bridge interaction with airflow

Field vs. Laboratory Correlation

Laboratory advantages:

• Controlled environmental conditions
• Intrinsic material properties
• Repeatable test conditions
• Elimination of installation variables

Field testing advantages:

• As-installed performance
• Workmanship effects included
• Real operating conditions
• Quality assurance verification

Typical correlation factors: Field air leakage often 2-5× higher than laboratory values due to:

• Installation imperfections
• Material damage during construction
• Joint and interface effects
• Settling and structural movement

Related Test Standards

Supporting Methods

Performance Verification Standards

• ASTM E1424: Rating of Joints by Air Leakage
• ASTM E2357: Air Leakage of Building Envelope Joints
• AAMA 502: Voluntary Specification for Field Testing
• RESNET Standard 380: Whole Building Air Leakage Testing