What is a "water resistant barrier" (WRB), examples and misconceptions

Posted by: Matt Hoots // SawHorse Design + Build

A water-resistant barrier (WRB) is a material used in construction to prevent the intrusion of moisture into the interior of a building. It is an essential component of the building envelope, designed to protect the building from water damage, air infiltration, and heat loss. It is vapor open, meaning it has a perm rating so that moisture can travel through it to all the structures to dry out.

Examples of water-resistant barriers 

 

1. Building paper: This is a traditional WRB used for decades. It is made of asphalt-impregnated felt and is commonly used in wood-framed construction.

2. Housewrap: This is a modern WRB made of a synthetic material such as polyethylene. It is lightweight, durable, and easy to install. It is commonly used in wood-framed and steel-framed construction.

3. Rigid foam insulation: Some types of rigid foam insulation can serve as a WRB. These materials are installed on the exterior of the building and can provide both insulation and a moisture barrier.

4. Liquid-applied membranes: These are materials sprayed or rolled onto the exterior of the building. They form a seamless and durable barrier against moisture and are commonly used in commercial construction.

5. Structural sheathing: Some structural sheathings, such as plywood and oriented strand board (OSB), can serve as a WRB. These materials are typically installed on the exterior of the building and provide both structural support and a moisture barrier.  

 

Not all WRBs are equal, and several factors should be considered when choosing the proper one for your project.  Most builders focus only on the cost of the WRB, which is the leading factor for which one they use.  Building codes require tighter construction to prevent air loss so an air-tight WRB may be your best bet.

 

Common Misconceptions regarding WRB’s

 

1. WRBs are waterproof: One of the most significant misconceptions about WRBs is that they are waterproof. In reality, WRBs are designed to be water-resistant, not waterproof. This means that while they can prevent moisture intrusion into the building, they are not completely impervious to water.

2. WRBs are only needed in wet climates: Another misconception is that WRBs are only needed in areas with high levels of rainfall. However, buildings can be subjected to moisture intrusion from snow, wind-driven rain, and condensation, even in dry climates.

3. WRBs are unnecessary in buildings with stucco or brick exteriors: Some people believe buildings with stucco or brick exteriors do not need a WRB because these materials are inherently water-resistant. However, even stucco and brick can allow moisture to penetrate the building if they are not properly installed.

4. WRBs are only necessary for new construction: Another misconception is that WRBs are only needed in new construction. However, older buildings can also benefit from installing a WRB, particularly if they are renovating or retrofitting.

5. WRBs are only needed on the exterior of the building: While WRBs are typically installed on the exterior, they can also be installed on the interior in certain situations. For example, in areas with high humidity levels, an interior WRB can help to prevent the intrusion of moisture into the interior of the building.

 

If you'd like to learn more about proper air sealing and insulation, and weatherization, check out these related topics:

• Pros and Cons of an airtight house
• Why Air Sealing and Insulation are Both Essential
• What is ACH50, and why does it matter?
• The “Perfect Wall” Defined and Demonstrated
• 50% of the "Perfect Wall" Control Layers with One Product

And stay tuned for more information about proper ventilation and optimizing comfort and indoor air quality in airtight homes.  You can also always visit the #1920sMakeoverATL page for information related to this exciting project.