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Perspectives in Design | Demystifying the Nomenclature: Is it an Air Barrier, WRB, Vapor Barrier, or Coating of Peanut Butter?

Perspectives in Design | Demystifying the Nomenclature: Is it an Air Barrier, WRB, Vapor Barrier, or Coating of Peanut Butter?
February 10, 2020


by John Rock, AIA

Here, I offer takeaways from the Air Barrier Symposium held at the Center for Architecture and Design in Philadelphia. One of the many architectural elements needed to meet today’s energy codes, air barriers are key components to the design and construction of buildings. Yet, despite their value, there is still much debate over the proper way to identify them.

Changes made to the International Energy Conservation Code (IECC) since the 2009 edition have greatly increased the requirements for control of air leakage at the building envelope. “Air Barrier” is the term identified in the IECC; not vapor barrier, permeable/impermeable, breathable/non-breathable, or the many other names used to describe the component of the building meant to keep the conditioned air in and protect against moderate moisture infiltration. While those other terms may fall within the scope of the term air barrier, they may or may not satisfy the requirements of the energy code for air infiltration.

The air infiltration requirements do not specifically address water vapor, however, Chapter 14 of the International Building Code (IBC) 2018 does require many buildings to have a water-resistive barrier for preventing condensation in the exterior wall assembly (with some exceptions). This need is generally fulfilled by many air barriers, according to one of the Symposium’s main speakers, Roy Schauffele, who asserted during his presentation that many air barriers undergo more testing for water infiltration than for air. When it comes to designing the envelope of the building, many products or systems will fulfill both of these requirements simultaneously and can have other inherent advantages specific to different conditions.

As the field of chemistry continues to advance, confusion regarding weather resistive membranes is understandable given the vast number of options on the market. One resource mentioned by Mr. Schauffele for learning about air barriers is the Air Barrier Association of America (ABAA) website. There is a page on the site that lists known air barrier products that have passed the evaluation criteria set forth by the ABAA. This page has over one hundred separate products, all complete with testing data in conformance with ASTM E 2357 Standard Test Method for Determining Air Leakage of Air Barrier Assemblies.

The use of some type of weather resistive barrier product to protect buildings and its expensive conditioned air was documented at least as early as the 1930’s, when Professor F. B. Rowley of the University of Minnesota published a study advocating for the use of a vapor barrier to combat moisture within the wall assembly. Since then, research has evolved in many ways due to better testing, case studies of failed applications, changing manufacturing processes, and improvements in materials science. One anecdote used by Schauffele to illustrate the change in materials over the years was to explain that disco led to the failure of some roof systems in the 1970s.  As polyester fabrics became readily available, disco fever took hold and much of the clothing of the time was designed with polyester, and not cotton (rag felt) driving the cost down and causing some roof membrane manufacturers to contain less cotton and much more polyester. This led to many system failures due to the fact that the tensile strength of polyester was much lower than that of the cotton fiber it was replacing.

One place to start sorting out the hundreds of different air barriers to choose from is to break down the field into different categories. Schauffele explained that the main goal of any air barrier is to prevent the air that you paid to heat or cool from escaping the building. He outlined a number of different products that have been used to achieve this end: self-adhered membranes, fluid applied membranes, sprayed polyurethane foams, board stocks such as drywall, building wraps, and exterior sheathing products with a pre-applied membrane. What is most critical for all these systems to qualify as air barriers is continuity. For example, drywall by itself has been qualified as an air barrier, but some painstaking extra steps need to happen during installation in order to meet the standard set forth by the IECC.

According to Schauffele, just about anything can pass the ASTM E2178 air barrier material test if applied in a continuous manner, including peanut butter. Yes, peanut butter. This was proven when the ABAA tested an assembly with 20 mils of creamy peanut butter applied, and had it pass the test. Passing an initial test alone is only half the battle – in the end, you need a product that can last the life of the building as well as pass the test. Using a listed ABAA Evaluated Assembly can be one way to give owners certain assurances of performance when it comes time to procure the building envelope assembly.

In addition to air barriers, another topic covered at the symposium was flashing. Covered by Craig Wetmore, flashing was identified as the critical counterpart to any air barrier system. Flashings provide a way for the air barrier system to terminate at the bottom or top of a wall, or at the joint between two separate systems. Often times, flashing is the primary cause of failure due to both improper installation and by not selecting the correct flashing for the application. For instance, some flashings need to be flexible to withstand movement of different materials as they expand or contract in the hot or cold weather. Other flashings need to be able to span a gap between different parts of the wall assembly. Lastly, there is awareness required on the part of material compatibility. One material to be cautious of using is aluminum.  If aluminum comes in direct contact with concrete, the chemicals in the concrete can cause the aluminum to oxidize and corrode at an increased rate.

Now that the nomenclature has been demystified, we can confidently identify air barriers just as they are – air barriers. Thanks to AIA Philadelphia’s Air Barrier Symposium and its speakers for providing useful knowledge of materials and methods to help designers deliver comfortable and durable projects.

Credit to Roy F. Shauffele, FCSI, CCPR, FABAA, CABS, LEED Green Assoc. who is available for further air barrier questions at (210)-859-3749. Credit also to Craig Wetmore, CSI, CDT who can answer through wall, material selection & sustainability questions related to flashing and can be reached at (207) 712-2261.

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