Combination Air and Water-Resistive Barriers in Exterior Walls

Thin fluid-applied membranes can have the same or better performance than other options
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Sponsored by Dryvit Systems, Inc.
Peter J. Arsenault, FAIA, NCARB, LEED AP

Learning Objectives:

  1. Explore the latest code and design standards for development of continuous air barrier requirements for exterior wall assemblies.
  2. Assess the various air barriers and water resistive barriers (WRBs) on the market today.
  3. Analyze the differences between the various product types for performance and installation characteristics.
  4. Investigate the difference between thinner fluid-applied film, polymer-based combination air/WRBs and those that are thicker, asphalt-based air/WRBs.


This test is no longer available for credit

The design and performance of exterior walls has received a lot of deserved attention in recent years. Building science research, code updates, and sustainable building design innovation have all contributed to greater understanding and implementation of best practices related to air, water, and vapor barriers in exterior walls. All three of these barriers are important to not only control energy usage in buildings but also to assure the longevity and durability of a wall system across its life cycle. Nonetheless, the growth in available information can cause confusion on what really works in a particular wall assembly in a particular climate. Worse, in a rapidly changing industry, building and design professionals sometimes rely on outdated information and fail to recognize the benefits of the latest, well-tested and proven products or systems.

International Building Code—Leading the Way on Wall Performance

During the past few decades, the International Building Code (IBC) has been regularly updated to be much more specific regarding requirements for exterior wall construction. Some of these are prescriptive requirements meaning that compliance is based on following a prescribed level of performance that may vary by location or situation. For example, if we were discussing fire egress requirements in a commercial building, we would see that the number of exit doors required by the IBC is calculated based on prescriptive requirements related to occupancy, area, and use. By contrast other code requirements are simply mandatory regardless of situation, meaning that they must be present and they must meet minimum standards of performance. In our egress example, the presence of opening protectives (automatic door closers) is a mandatory code requirement on every exit door regardless of other factors. When it comes to exterior walls, air, water, and vapor barriers fall into the mandatory category—all are required in virtually all cases with only one variable for vapor barriers based on location.

Exterior walls of all types need to meet updated code requirements for continuous barriers against air, water, and vapor.

Photo courtesy of Dryvit Systems, Inc.

Exterior walls of all types need to meet updated code requirements for continuous barriers against air, water, and vapor.


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Originally published in Architectural Record
Originally published in November 2014