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WRB’s: Getting Beyond the Basics

Read on to learn a few things you might want to know about WRB’s but were afraid to ask.

A weather-resistive barrier (WRB) is the anchor of a weatherization system. It protects the walls of a structure from water that penetrates the cladding. 

Although exterior cladding (siding, stucco, etc.) will never be 100% impermeable, the role of the WRB is to provide a second layer of protection that keeps the wall assembly dry and free from moisture damage should some water find its way through.

There are several important things to consider when selecting the WRB for your project.

Application Method

Mechanically attached

The most common type of WRB for residential, multifamily and light commercial structures, available in several types of materials:

Asphalt Saturated Kraft Paper – excellent substrate in dryer climates and under masonry and stucco

Woven polymeric housewraps – plastic tapes woven in 2 directions and coated with a waterproof film. Often these are micro-perforated to allow vapor to escape. These meet code requirements in many areas

Spun bonded, non-woven housewraps – a technically advanced barrier that keeps bulk water out, while allowing the structure to “breathe”

Integrated structural panel with weatherization

An all-in-one weatherized panel with an affixed weather barrier. Joints must be taped thoroughly to complete the weatherization envelope.

Self-adhered weather barrier

Repels water and reduces air leakage to promote energy efficiency. Typically, this type of WRB self-seals around nails—an added advantage.

Fluid applied

A WRB that is sprayed or rolled on, offering continuous coverage and energy efficiency. Many self-seal around nails.

Performance characteristics

In addition to application method, WRB’s may be selected based on performance characteristics best suited to climate or cladding. Considerations include:

Drainage efficiency

In wet areas, additional drainage capabilities may be required. WRB’s that offer high drainage performance generally have some type of embossed or textured face, enabling water to drain away more efficiently. Learn more about drainage in our blog post.

Surfactant resistance

Wood siding may leach a chemical surfactant that can cause water to penetrate some WRB’s. Power washing with certain detergents and cleaning solutions containing surfactants may also get behind cladding, producing the same harmful impact.

UV resistance

Some WRB’s offer extended resistance to UV rays from the sun. This is an important consideration for larger projects, such as multifamily construction in which the WRB will be exposed for a longer period of time before being covered with cladding.

Stucco and masonry

Building code requires 2 layers of WRB behind these types of claddings. Asphalt Saturated Kraft paper is a good choice for the “sacrificial layer” that is adjacent to the stucco/mortar. Even if some of the stucco sticks to this layer, the second layer will act as a WRB and allow the structure to dry.

Vapor Permeability

Weather-resistive barriers can be either vapor permeable or vapor impermeable. In most climate zones, residential buildings typically use a vapor-permeable weather-resistive barrier.

Choosing the right weather-resistive barrier is critically important to the effectiveness of any building envelope system. Understanding the key differences between weather-resistive barriers will help ensure you make the best decision for your next project.

Contact a Henry weatherization expert for advice and support on your next job.

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