What is the function of a water-resistive barrier?

A water-resistive barrier plays a key role in the building envelope. Often referred to by the acronym “WRB,” the functionality of a water-restive barrier is sometimes confused with a vapor barrier, as both control the movement of moisture.

Further confusion can surround these terms because a single membrane can serve as an air, vapor and water-resistive barrier. Then there is the “WRB” acronym itself, which is often used interchangeably to refer to a water-resistive barrier and a weather-resistive barrier. To help clear up some of these “WRB” misunderstandings, let’s start with a basic definition:

What “WRB” performance do you need?

Again, the use of the WRB acronym is common in the construction industry. But depending on the source and context, the term may be meant to refer to either a “water” or a “weather” resistive barrier. While the terms are often used synonymously, each “WRB” has a different function.

In the most basic terms, a water-resistive barrier will resist the intrusion of bulk water, while a weather-resistive barrier will resist the intrusion of air and bulk water. The protection that a weather-resistive barrier provides is more robust and requires that all laps and terminations are sealed to resist both air and water intrusion.

Accordingly, many manufacturers of polymer-based barriers – or building wraps – will differentiate their products as either a water- or a weather-resistive barrier, with the latter providing the added benefit of air barrier protection for wall assembly enclosures.

International Building Code (IBC) mandates for water-resistive barriers reflect this distinction as well and apply to residential and low-rise structures. For commercial and high-rise projects, the codes generally specify the use of a weather-resistive barrier, as a higher level of building envelope performance is essential.

Whatever the WRB, installation matters

Understanding the performance expectations of the specified WRB – resisting water or resisting air and water – is important for designers and installers alike. That’s because installation procedures will vary for each type of barrier. But whatever its intended function, a WRB must be properly installed to provide a continuous barrier.

That means the WRB must be fully sealed at all the spots where water (and/or air) could potentially breach the building envelope. Such trouble spots are usually at the transitions between above- and below-grade enclosures, flashings around doors and windows, and sealing around architectural details or other penetrations.

Have more questions about WRBs?

To design and install an effective building envelope, understanding the differences between water- and weather-resistive barriers, and the roles of air and vapor barriers, is essential. But developing that understanding is just the beginning.

If you need more information about WRBs – either water-resistive barriers or weather-resistive barriers – or have any questions about the building envelope for your next project, consider consulting with the experts at Henry® Company. For more than 80 years, our solutions have been helping designers and installers control the flow of water, air and vapor throughout the building envelope. Today, our Building Envelope Systems® include a wide range of compatible products and solutions designed to help you meet your challenges.