All photos courtesy of TYPAR

WRBs are vital to the construction of new residential and light commercial, multifamily, and mixed-use buildings to achieve occupant well-being, safety and comfort. New WRB technology can meet and exceed evolving standards for healthier buildings and homes.

Weather-resistant barriers (WRBs) are essential in the construction of new residential and light commercial, multifamily and mixed-use buildings. They help achieve occupant well-being, safety and comfort. With more people working and playing at home, as well as more commercial buildings constructed to higher standards, new WRB technology can meet and exceed standards for healthier buildings and homes. Technology can be designed to meet building requirements, a variety of climates, and the effects of climate change. Indoor air quality (IAQ) should increase comfort and even foster well-being for building occupants. Indeed, the EPA has shown that on average, people spend up to 90 percent of their time indoors. Indoor spaces need to be safe, durable, comfortable and efficient. People want to work and live in healthier buildings and homes.

The terminology and function of WRBs can be confusing, making it difficult to compare products. Sometimes WRB may refer to a water-resistive barrier, but there is a difference and they have distinct purposes. For the sake of this piece—and taking the definition from The American Architectural Manufacturers Association—a WRB is a weather-resistant barrier, a surface or wall responsible for preventing air and water infiltration into the structure’s interior.

WRBs used to be categorized as products that prevent water from entering buildings while under construction. Today, WRB products comprise a broader product group that prevents water, air, thermal, and vapor (or WATV) transmission from transferring from inside or outside of a home or building. WRBs, as part of a tight building envelope, can reduce heating and cooling costs—up to 15 percent in some cases—while protecting buildings from harsh elements and improving comfort for occupants.¹

Section 1: Why WRBs?

Energy-efficient buildings with comfortable environments need air tightness and reduced thermal bridging to lower heating and cooling costs, and controlled moisture is necessary to keep building occupants comfortable and healthy. WRBs are critical in meeting improved IAQ and other needs in modern homes and buildings.

Modern WRBs are made of lightweight, synthetic material that are applied to homes and commercial buildings to protect them against air leaks, water, and moisture infiltration. They function as a shell for buildings—liquid that has penetrated the exterior finish can’t get through, but water vapor can escape. Though resistant to weather, they allow water vapor to pass from inside a building to its exterior, which prevents mold and rotting and increases a building’s energy efficiency and comfort. These materials are resistant to damage during installation, and they provide exceptional air- and water-blocking performance.

One of the differences between WRBs—sometimes referred to as “housewraps”—and building paper is the additional gap created by spacers, allowing moisture to drain from wall assemblies more quickly. Also the drainage channels form an unobstructed path behind cladding, avoiding the possibility of ponding along siding edges with traditional barriers.

Scientific history of WRBs

Already applied in successful reconstruction of dated European buildings, exterior insulation and finish systems (EIFS) were introduced in the United States in 1969. The evolution of wraps and barriers, starting in the early 1970s, saw innovations in different types of sheathing technology; these iterations are responsible for most of the water and air resistance in wall assemblies to date. The housewrap of that time—spurred by the energy crisis calling for more efficient products—provided a way to seal the exterior of a building and reduce air leakage. But other benefits of these barriers were apparent, including the ability to withstand high winds and offer flexibility at lower temperatures, and the ability to restrict air flow. In addition, the barriers were condensation-reducing and lightweight. The 1970s also brought asphalt-saturated felt paper, required by building codes to be installed as a WRB instead of paper-faced gypsum sheathing.

Concerns about energy conservation and product durability in the 1980s brought about gypsum board sheathing that replaced the paper facing with a fiberglass mat facing. This could be exposed to normal weather for longer periods of time compared to paper-faced sheathing. The fiberglass mat surface was a primitive but effective WRB surface. Fibrous building wraps were used on both residential and commercial construction mostly to create an air barrier, although some provided a WRB, too.

Other rigid board stock products came into the market in the ‘90s, and were meant to act as a sheathing or substrate behind cladding on an exterior wall. Most of these products needed to be covered quickly since they deteriorated rapidly in the elements. In the following decade, changes in the International Building Code (IBC) required WRBs to be applied to sheathing. Membranes were applied over the sheathing, but they were labor-intensive when it came to irregular areas. Of course, all the products and older versions of the modern technology are available and used to some extent today, which can complicate things, but this piece will focus on new construction.

About 10 years ago, the technology for fluid-applied membrane barriers continued to develop and they became more effective, allowing for thinner applications. Testing showed they were highly effective as a WRB and air barrier. The next innovation in this technology offers both a WRB and air barrier directly in the fiberglass-mat-faced gypsum sheathing, as well as an arsenal of other means to completely seal other openings. This reduces the dependence for effectiveness on the installer and utilizes the best products and their capabilities.

It is important that all professionals are current on these developments to ensure using the best-available solution for a project. The installer needs to be qualified and to demonstrate completed training and experience with WRB installation and then submit to testing and inspection once installation is done. A new building’s envelope should be built to control air leakage, avoid condensation in the interior wall assembly, and prevent water intrusion. Joints, penetrations, and paths of moisture and air infiltration should be made as watertight and airtight as possible but also be flexible, allowing for some movement of the system with variations in temperature and moisture.

It is important that professionals are qualified to install WRBs and then submit to testing and inspection once installation is done. A new building’s envelope should help control air leakage, avoid condensation in the interior wall assembly, and prevent water intrusion.

Benefits of WRBs for occupants

WRBs are used today in new construction for the benefit of occupants of residential and light commercial, multifamily and mixed-use buildings. When installed and sealed correctly, WRBs help minimize wind and air leaks that would otherwise create hot or cold zones inside a building. They also minimize water and moisture infiltration and are vapor-transmissible, reducing condensation and moisture-related problems like mold and mildew, bugs and rot.

WRBs offer further durability within high-performance energy systems. They help increase a building’s total insulation R-value and help control moisture in new buildings so they prevent mold growth and become more energy-efficient, less costly to heat and cool, and more comfortable. WRBs improve the efficiency of a building’s HVAC system and, by keeping building materials dry, they help minimize maintenance costs. All of this contributes to occupants’ comfort and well-being.

WRBs offer further durability within high-performance energy systems in new buildings; they help increase total insulation R-values, help control moisture (and hence, mold), and increase energy efficiency, all helping to minimize maintenance costs.

Climates, weather, and WRBs

Different climates produce rain, heat, humidity, snow, and wind. High humidity and extreme temperatures often lead to moisture flowing from warm to cold (carried by air movement through leaks in the wall assembly) and condensing on the colder surface. Rain, driven by wind, can be forced into small openings in the exterior cladding such as joints, laps, utility cut-outs, electrical outlets and nail holes. Wind can create a negative pressure within the wall assembly, siphoning water into the wall. Some “reservoir” claddings such as brick, stone, and stucco can absorb and store moisture, which the sun then forces into the wall assembly, a process referred to as solar drive.

Geography and annual rainfall matter when it comes to WRBs. The Building Enclosure Moisture Management Institute recommends that any area that receives more than 20 inches of annual rainfall should use enhanced drainage techniques, while areas receiving 40 inches or more should utilize rainscreen design, regardless of cladding. The orientation of the wall in question, the overhang, altitude, and even nearby trees also can affect how much water can get in and how likely it is to dry.

Building scientists and other experts agree that no matter how tightly a building is constructed or how well it’s insulated, and no matter what type of cladding and how skillfully installed, moisture always will find a way into the building enclosure. This infiltration can undermine structural integrity, cause exterior surfaces to deteriorate, and shorten the life of paints and stains. Mold and rot can contribute to structural damage but also pose serious health risks. The main objective is ridding the wall assembly of moisture as quickly as possible when it gets in.

Changing building codes and the WRB market indicate growth

As part of the complete building envelope, WRB products continue to evolve and the WRB market will continue to expand.

There are many moisture management products available, among them traditional felt paper, rainscreen systems, caulks, sealants and self-adhered flashing membranes. Choices are expanding, and they are spurred by advances in technology, desired green certification and other factors.

WRBs are no longer optional as they are required by all current building codes—and recommended by all building experts. For example, the 2018 IECC residential energy codes, adopted already by several states, require additional proven energy efficiency measures based on higher insulation values, tighter homes, and improved moisture management. Commercial building construction is moving to holistic design approaches favoring energy efficiency, internal environmental quality, and prolonged building durability. Zero-energy initiatives and others emphasizing innovation in integrated design for the entire building envelope continue to gain attention. All this drives the need for materials and systems that perform successfully over a wide range of conditions.

WRBs increase durability of new buildings in any climate. Effective air sealing, efficient HVAC systems, and fitting insulation are all part of best practices for new buildings, no matter the environment. Without a WRB, sheathing and other parts of the wall assembly would be much more susceptible to damage from the elements.