IECC Requirements for Continuous Air Barriers

CodeWatcher air barrier

A weather-resistive barrier, combined with properly installed flashing and tapes, results in efficient air barrier assembly.

 

Quite simply, an air barrier is a material or system of materials designed to control airflow between conditioned and unconditioned spaces. It serves as the primary air enclosure boundary separating indoor and outdoor air. Within multi-family construction, the air barrier system also separates the conditioned air from any given unit and adjacent units. Air barriers also typically define the buildingCodeWatcher Typar enclosure’s pressure boundary. Gypsum board, liquid-applied membranes and sprayed polyurethane foam (SPF) insulation are all examples of air barrier materials. However, in this article, we will focus on the use of building wrap assemblies to achieve air leakage requirements set forth by the International Energy Conservation Code (IECC).

What Does the Code Say?

The requirement for continuous air barriers was first added to the 2012 IECC and there are a number of ways to meet this requirement. As part of this mandate, the code requires all new construction and additions to be visually inspected, as well as pressure-tested, as standard operating procedure.

For an individual building material to be classified as an air barrier, its air permeance (i.e. amount of air migrating through materials rather than holes or gaps) must be equal to or less than 0.02 L/(s-m2) @ 75 Pa (0.0004 cfm/sf @ 1.57 psf) when tested in accordance with ASTM E2178, Standard Test Method for Air Permeance of Building Materials.

The requirements for an air-barrier assembly are somewhat less stringent, and are measured in terms of air leakage. When tested in accordance with ASTM E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies, the subject must be 0.20 L/(s-m2) @ 75 Pa (0.04 cfm/sf @ 1.57 psf) in both directions (i.e. infiltration and exfiltration), which works out to 10 times greater than a building material alone. This method is intended to simulate the performance of various air barrier materials and accessories when combined into an assembly. This ‘air barrier assembly is defined as a group of materials assembled and joined together to provide a barrier to air leakage through the building envelope. For example, use of a weather-resistive barrier (WRB), combined with properly installed flashing and tapes, would be considered an air barrier assembly.

Building Wraps Functions as Air Barrier

As mentioned previously, several materials can impede air movement through a wall assembly, however certain technologies perform better than others. For nearly 50 years, plastic building wraps made of polyethylene or polypropylene fabric have been a popular option due to their durability and ease of installation.

Plastic building wraps are typically either woven or non-woven—an important difference when it comes to specifying an air barrier. Woven polypropylene with slit-film perforated coating typically offers two months of UV resistance, but most types do not meet ASTM requirements for air-barrier materials and are not surfactant-resistant. That said, spun-bonded polypropylene with micro-porous coating, on the other hand, often meets ASTM requirements for air barriers, is resistant to surfactant chemicals and offers six months UV exposure resistance. Depending on the type of cladding to be installed over the wrap, and how long the wrap will be exposed to the elements before the cladding’s installation, these additional durability benefits may be important.

The use of air barriers is being driven by advances in building codes and increased awareness of their ability to support sustainable, comfortable buildings. However, not all air barriers are equal in performance or design, and there is not one solution suitable for all climates, regions, and project conditions.

Understanding how air-barrier materials and systems are evaluated, and knowing their performance characteristics, helps design professionals find the right solution for their project needs. Approaching air barriers from a holistic view and evaluating the entire system—rather than just an individual material—results in a tighter and far more durable enclosure that can stand the test of time.