Selecting and achieving the proper air barrier

EIFS can also be specified on existing buildings, as in the case of this hotel-turned-condo.
EIFS can also be specified on existing buildings, as in the case of this hotel-turned-condo.

CAN/ULC S134-92
This is a large-scale fire test for wall cladding assemblies. It was developed at the National Research Council-Institute for Research in Construction (NRC-IRC) National Fire Laboratory (NFL) as part of a research project to evaluate the best method for evaluating wall cladding performance when subjected to a fire source. EIFS assemblies were early subjects of research. Of the many methods assessed, this test best simulated actual fire performance. It is difficult to successfully simulate a real fire with a small-scale test.

The test apparatus is 10 m (33 ft) tall with an opening representing a window and a room behind the opening where the fire is generated. This simulates fire consuming all the combustible materials in a room, resulting in flames that burst out the ‘window’ and expose the wall surface. Propane is the fuel for the fire test, which runs for 25 minutes. The test measures the flame spread within the cladding assembly, how far it spreads up the exterior wall surface, and how much energy is contributed by the cladding.

For those who have witnessed the procedure, it is a hair-raising and singeing experience to see a roiling ball of plasma suddenly ‘flash over’ and billow out the window and up the wall. Casual observation is not an option for this test. Even standing on the other side of the laboratory, those watching are compelled to step back from the sudden flux of radiant energy as the fire bursts from the opening. (One develops a huge respect for firefighters who face this on a regular basis.)

Where do air barriers fit in this test? Foam insulations used in wall assemblies such as
EIFS and in other cladding cavities have been tested to demonstrate compliance with the code requirements. The question for the specifier is whether these assembly tests include an air barrier. This has become an issue in the United States where a similar test is run—National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components.

Recent concerns have been raised that some previously tested assemblies do not meet the requirements if an air barrier membrane is added. What had been treated as a minor combustible element appears to have a significant detrimental influence on performance. Now that air barriers and continuous insulation are both new requirements in the United States under the International Building Code (IBC), many companies are fire-testing assemblies to demonstrate compliance.

A specifier should obtain an evaluation that the air and moisture barriers used in a wall assembly have met the requirements of NBC Part 3.

Joint Base Lewis-McChord (Washington) has a new 10,668-m2 (35,000-sf) building—the SOF Aviation Battalion Education Center. It boasts a liquid-applied water-resistive barrier (LA-WRB).
Joint Base Lewis-McChord (Washington) has a new 10,668-m2 (35,000-sf) building—the SOF Aviation Battalion Education Center. It boasts a liquid-applied water-resistive barrier (LA-WRB).

Liquid-applied water-resistive barriers
The evaluation of LA-WRBs has taken durability requirements beyond normal material testing.2 Evaluators asked the question, “What happens at joints?” In the United States, the ICC Evaluation Service (ES) determined racking a full-scale mockup before water penetration testing would be required. In Canada, initial research showed racking resistance was doubled with a LA-WRB. CCMC decided racking would be reduced so this type of stress would not be a durability factor.

The alternate test chosen was to bend the joint outward, the purpose being to stress the membrane over the joint to failure. Samples that survived were placed in a vice-like device and the joints were stretched 40 per cent. While stretched, the samples were subjected to environmental cycling; the joints were then tested for water leakage using a modified version of ASTM E 96, Standard Test Methods for Water Vapour Transmission of Materials, with 25 mm (1 in.)
of water above and desiccant below.

Moisture gain in the sheathing was measured. In the initial research conducted by Forintek Canada Corp., in Québec City, researchers noted samples left in the test apparatus for 82 days did not exhibit mould growth.

The CCMC Technical Guide for EIFS and, ultimately, ULC S716.1, require LA-WRB testing for:

  • bond strength to the substrate;
  • water absorption co-efficient;
  • water vapour permeance;
  • accelerated weathering resistance and nail popping resistance; and
  • the aforementioned joint durability testing.

The new CCMC Technical Guide for LA-WRBs requires testing based on both the ICC-ES Acceptance Criteria and the CCMC Technical Guide for EIFS, Appendix 4. Additionally, fastener penetrations are tested for water penetration under a range of pressure differences after heat aging. The LA-WRB performed six times better than the standard code-recognized material—building felt.

LA-WRBs have been tested to ASTM E 2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies, and meet the requirements for an air barrier system. The system test includes joints, secondary connections, fasteners, and penetrations.

In addition to durability testing, LA-WRBs have been fire-tested as standalone components and as components in assemblies. In the United States, materials are required to be tested to ASTM E 84, Standard Test Method for Surface-burning Characteristics of Building Materials (similar to Canada’ s ULC S102, Standard Method of Test for Surface-burning Characteristics of Building Materials and Assemblies), to obtain a flame spread rating. Typical results are less than 25, which ranks a material in the Class A category. In Canada and the United States, EIFS assemblies with expanded polystyrene (EPS) insulation that is 100, 140, and 300 mm (4, 5.5, and 12 in.) thick have been successfully tested with a LA-WRB.

Air barrier use in building and construction is an important part of sustainable design, and is a required component in many green building rating systems and codes. These include:

    • Canada Green Building Council’s (CaGBC’s) Leadership in Energy and Environmental Design (LEED);
    • U.S. Department of Energy’s (DOE’s) Energy Star;
    • American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, and ASHRAE 189, Standard for the Design of High-

performance Green Buildings; and

  • National Energy Code of Canada for Buildings (NECB).

Air barriers have come into Canadian and U.S. building codes following different paths.

Originally, NBC introduced the requirements for air barriers to minimize condensation and bulk water entry into the building envelope. The importance of this was confirmed with Canada’s implementation of objective-based codes and recognition of the airtightness contribution to health and safety of the occupants. In the United States, air barriers have become a requirement of the International Energy Conservation Code (IECC) in recognition of a National Institute of Standards and Technology (NIST)3 study that calculated 40 per cent of energy consumption in cold climate buildings is lost due to air leakage.

Both approaches are valid and are converging. In December 2011, NECB was published with the energy conversation requirements for air barriers. Requirements for air barriers as protection against water condensation and penetration are currently being discussed for inclusion in IBC in the United States. The value of air barriers is now well recognized. The issues that remain are regarding air barrier materials now being promoted to comply with all aspects of the code, whether they are durable, and if they meet the specific requirements for the project.

1 An air barrier ‘material’ is a single component that has airtight properties. An ‘assembly’ is a series of materials integrated to become a single airtight component (e.g. a window). The complete air barrier around a building is the air barrier system.
2 An example of ‘normal’ material testing is ASTM E 96 water vapour transmission, which tests for a single characteristic of a material and infers performance. With the LA-WRB, extensive testing for durability under environmental stresses was required. Typical sheet ‘sheathing membranes’ will not pass the testing LA-WRBs go through.
3 For more, see “NIST Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use,” by Steven J. Emmerich, Timothy P. McDowell, and Wagdy Anis (June 2005).

John Edgar is Sto Corp.’s technical director for Canada. He has worked for the company for more than 20 years, and is actively involved with the Air Barrier Association of America (ABAA), EIFS Council of Canada, Underwriters Laboratories of Canada (ULC), and numerous research organizations evaluating exterior insulation finish systems (EIFS) and liquid-applied  water-resistive barriers (LA-WRBs). Edgar has also served 13 years on the Environmental Separation Subcommittee for the National Building Code of Canada (NBC). He can be contacted via e-mail at

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