Liquid applied water resistive barrier
Photo Courtsey of Fine Homebulding

Every year, many new residential and commercial buildings are constructed. In order to keep the inside of these buildings moisture-free, construction professionals apply a water-resistive barrier (WRB) over the sheathing material (e.g. plywood, OSB, glass mat panels) on exterior walls before the cladding is installed.

There are several options for WRBs, including, but not necessarily limited to: mechanically-fastened paper-type or asphalt-based barriers, self-adhering housewraps, liquid-applied coatings, foam plastic sheathing, and “all-in-one” structural sheathing with a factory-laminated WRB. This post focuses on liquid-applied coatings, which are also known as fluid-applied coatings and water-resistive coatings.

What Are Liquid-Applied Water-Resistive Barriers?

In short, a liquid-applied WRB is a coating designed to act as a water barrier on the exterior walls of a structure. These coatings can be sprayed or rolled onto the exterior sheathing and can also be used as an intervening material between two layers of exterior cementitious coatings.


Many construction professionals like liquid-applied WRBs because they are easy to apply and can be used on many sheathing and construction substrate materials, such as wood, vinyl, metal, and gypsum sheathing. Additionally, if any spots are missed during the application process, installers can simply touch up these areas.

Qualification Testing

Before liquid-applied WRBs are approved for use, they have to meet specifications like ICC-ES AC212 in order to establish compliance with building codes. AC212 requires tests such as:

  • Coating bond to sheathing per ASTM C297
  • Weathering and hydrostatic pressure tests
  • Water vapor transmission per ASTM E96
  • Freeze-thaw cycles
  • Water penetration resistance per ASTM E331
  • Optional air barrier testing per ASTM E2178
  • Fire test depending on the intended end-use

These tests help to ensure that liquid-applied WRBs are durable and fit for their intended use.



About ICC NTA, LLC: As an accredited third-party agency and part of the International Code Council (ICC) Family of Solutions, ICC NTA provides code evaluation, inspection, engineering, plan review, and product testing services, as well as independent quality and standards compliance verification for building product manufacturers. With offices, testing labs, and training facilities in Nappanee, Indiana and Bryan, Texas, ICC NTA serves residential and commercial builders, code officials, manufacturers, and suppliers throughout the building industry.