What ASTM E2178 Measures
Air permeance describes how much air passes through a material for a given area at a given pressure. ASTM E2178 measures this rate at several pressure differentials and uses the result to calculate an assigned air permeance value at 75 Pa, the reference pressure used for comparing products against one another. Results are reported in litres per second per square metre, L/(s·m²), at 75 Pa. The standard treats SI units as the standard of record and does not include imperial equivalents.
The current full title of the standard is Standard Test Method for Determining Air Leakage Rate and Calculation of Air Permeance of Building Materials. Earlier editions carried the shorter title, Standard Test Method for Air Permeance of Building Materials. Confirm the current edition year against the ASTM store before publication, since editions are periodically revised.
Which Materials Are Tested
ASTM E2178 was written to assess flexible sheet and rigid panel-type materials, tested at a 1 m × 1 m specimen size. In practice, the method is applied to any material intended for use as an air barrier, including:
- Fluid-applied membranes
- Self-adhered sheet membranes
- Spray foam insulation
- Mechanically fastened commercial building wraps
- Board stock air barriers
How the E2178 Test Works
The procedure follows a consistent sequence in an accredited lab:
- The specimen is mounted on a test chamber, and a polyethylene film is placed over it and sealed to the chamber frame.
- Tare readings are taken first. The extraneous air leakage of the test apparatus itself is measured at 25, 50, 75, 100, 150, and 300 Pa.
- The film is then cut open, and total air leakage through the specimen is measured at the same six pressures, with airflow corrected to standard temperature and pressure.
- A durability check follows the peak reading. After the 300 Pa measurement, leakage is remeasured at 100, 75, and 50 Pa. If the two readings at a given pressure differ by more than 10 percent, the cause of the change must be identified and reported.
- The air permeance value at 75 Pa is calculated from the difference between the total leakage rate and the extraneous leakage rate established in the tare readings.
What a Passing Result Looks Like
Air barrier material specifications commonly reference a maximum air permeance of 0.02 L/(s·m²) at 75 Pa. This figure should be verified against the current National Building Code and BC Building Code text before it is published, since code references and editions change over time.
A passing result qualifies the material only. It does not guarantee that the finished building will be airtight, since installation quality, transitions, and penetrations are not part of this test. When reviewing a test report, look for the specimen count, whether the result is an average or an individual reading, and the outcome of the 10 percent recheck at the end of the procedure.
Where E2178 Fits: Material vs. Assembly vs. Whole Building
Air barrier performance is verified at three distinct levels, and each level answers a different question:
| Level | Test standard | What it answers |
|---|---|---|
| Material | ASTM E2178 | Does the sheet or board itself resist airflow? |
| Assembly | ASTM E2357 | Do the joints, fasteners, and penetrations hold up? |
| Whole building | ASTM E779 / E3158, CGSB-149.10 / 149.15 | How airtight is the finished building? |
Passing a test at one level does not imply a pass at the next. A material can perform well under ASTM E2178 and still allow significant air leakage once installed, if the assembly detailing or whole-building execution is poor. This is why large building airtightness testing remains a separate and necessary step for Part 3 projects, even when every specified material has passed material-level testing.
Why E2178 Matters in BC and Canada
Air barrier material requirements in the National Building Code and the BC Building Code rely on permeance limits established at the material level. CAN/ULC-S741, the Canadian standard for air barrier materials, uses ASTM E2178 as its underlying test method. Clause references and current editions should be verified before publication.
Under the BC Energy Step Code, airtightness targets are set and verified at the whole-building level, but the material permeance rating is the starting point that a design team relies on when specifying an air barrier system.
Limitations of the Test
ASTM E2178 does not address the installed air leakage performance of building materials. It is a laboratory measurement of the material alone, conducted under controlled conditions. Workmanship, substrate movement, aging, UV exposure, and site conditions fall outside its scope and are addressed through assembly and whole-building testing instead.
Conclusion
ASTM E2178 qualifies a material for use as an air barrier. It does not verify how that material performs once it is installed. Field verification closes that gap. Monolith Housing Solutions performs blower door and large building airtightness testing to confirm that specified air barrier materials deliver the expected performance once construction is complete, under the direction of founder Shahin Arvandi, a Level II Infrared Thermographer and Certified Air Tester with additional credentials as a Registered Energy Advisor and Certified Passive House Designer.
Frequently Asked Questions
Definition
- What does ASTM E2178 test for? It tests the air leakage rate of a building material at several pressure differentials and calculates its air permeance at a reference pressure of 75 Pa, indicating how suitable the material is as a component of an air barrier system.
- What is air permeance in building materials? Air permeance is the rate at which air passes through a material per unit area at a specified pressure difference, expressed in L/(s·m²).
- What is the difference between air permeance and air leakage? Air permeance is a material property measured under lab conditions, while air leakage generally refers to airflow through an installed assembly or building, which includes joints, penetrations, and workmanship.
Threshold and Results
- What air permeance rate qualifies a material as an air barrier? A commonly referenced maximum is 0.02 L/(s·m²) at 75 Pa, though the applicable threshold should be verified against the current code edition before it is used in a specification.
- Why is ASTM E2178 tested at 75 Pa? 75 Pa is the standard reference pressure used to compare air barrier materials on a consistent basis, though the test also records leakage at five other pressures to characterize the material’s behavior.
- How is an ASTM E2178 test report read? Check the specimen count, whether the reported value is an average or an individual result, and the outcome of the post-300 Pa recheck, which confirms the material’s leakage rate did not shift by more than 10 percent during testing.
Comparison With Adjacent Standards
- What is the difference between ASTM E2178 and ASTM E2357? ASTM E2178 tests a material sample in isolation, while ASTM E2357 tests an assembled air barrier system, including joints, seams, and penetrations.
- Is ASTM E2178 the same as a blower door test? No. ASTM E2178 is a material-level lab test, while a blower door test measures airtightness of an entire installed building or unit.
- How does ASTM E2178 relate to CAN/ULC-S741? CAN/ULC-S741 is the Canadian standard covering air barrier materials, and it uses ASTM E2178 as its underlying test method for determining air permeance.
Application
- Can spray foam be tested under ASTM E2178? Yes. Spray foam insulation is one of the material types commonly assessed using this test method when it is intended for use as an air barrier.
- Is house wrap an air barrier under ASTM E2178? Mechanically fastened commercial building wraps fall within the range of products this test method is used to assess.
- Does passing ASTM E2178 guarantee an airtight building? No. It qualifies the material only. Assembly-level and whole-building testing are still required to confirm airtightness once the material is installed.
