ASTM E779-19 – Standard Test Method for Determining Air Leakage Rate by Fan Pressurization

Improved airtightness performance on a building envelope helps reduce energy loss, operational energy costs, improve occupant comfort, enhance indoor air quality, sound proofing, limit moisture migration, mold growth and potentially deterioration through the building envelope. Airtightness Testing verifies this performance by providing objective verification that the air barrier system is performing as intended.

Testing is typically conducted after the air barrier system has been completed, and when the building preparations needed for the test can be completed. It is typically performed before occupancy so any deficiencies can be identified and corrected.  Note that building preparations involve building access to mechanical systems and have a potential impact on construction scheduling and coordination. The timing of it requires a high level of coordination between the general contractor, the trades, the airtightness consultant, and the owner. Early planning is beneficial, however even with early planning backup/continguency dates are recommended. An early discussion about the risks and pivot strategies with the airtightness consultant can be very helpful on a project.

Temporary calibrated fans are installed in exterior openings. The building is then pressurized and/or depressurized through a series of pressure differences across  the building envelope while airflow measurements are collected. These airflow measurements are used with the calculated envelope area to compute the building's air leakage rate.

Whole-building airtightness testing is commonly performed in accordance with ASTM E779 or ASTM E3158 or USACE Air Leakage protocol (in the United States), depending on project requirements and applicable codes.

A typical report includes building test conditions, pressure measurements, airflow data, calculated leakage rates, compliance evaluation, and recommendations for remediation if air leakage diagnostics testing is performed.

Air leakage diagnostic (qualitative) testing using various tools (smoke generators, infrared thermography cameras) can help identify sources of air leakage locations. Corrective air sealing measures may then be implemented, followed by retesting to verify compliance with project or code requirements.  Note that at substantial completion, typically the air barrier membrane and it’s transitions between assemblies are mostly covered up and inaccessible (e.g. behind cladding or drywall). Qualitative testing is best performed at early stages of construction to generally understand where workmanship deficiencies are. This is a more proactive approach than waiting till the very end of construction, when potential repairs are much more difficult, costly, and time consuming.

ASTM E779 can be used for any building archetype and can include  wide range of building types, including commercial, institutional, healthcare, educational, multifamily, and industrial facilities.  However it’s standard procedures do no provide clarity or flexibility with some of the challenges that are more specific to larger buildings, that ASTM E3158 and USACE tries to handle.

Recent energy codes (e.g. IECC 2021, IECC 2024, ASHRE 90.1 2011) increasingly require whole-building air leakage testing as a means of verifying envelope performance and demonstrating compliance with air barrier requirements.

ASTM E779 quantifies total air leakage. When combined with diagnostic testing (ASTM E 1186, also know as a qualitative test) with tools such as smoke testing, infrared thermography, or targeted investigations, teams can identify specific leakage pathways and prioritize repairs.