Air and Water-Resistive Barrier Systems

Professionally installed continuous air and water-resistive barrier (AWB) systems minimize unwanted air and water movement through the building enclosure. A high-quality AWB will also maintain its integrity and remain stable when exposed to high heat and UV rays, while offering excellent tensile strength, elongation, and tear resistance, which is critical to maintaining the continuous protection properties of an AWB.

Benefits of a high-performance AWB include

Managing incidental moisture in wall systems to reduce the potential for mold in the wall cavity, which protects the structure’s integrity
Limiting the loss of conditioned air (heating and cooling), to help ensure a more comfortable indoor environment
Facilitating lower energy use within the structure, which reduces operating costs while also reducing carbon emissions
Increasing air tightness, which when combined with a well-designed ventilation system, provides a healthier indoor environment by maintaining consistent humidity and temperature, which results in decreased potential for indoor mold growth
Lowering the initial investment in operating systems, such as HVAC, which often can be accomplished with an airtight building design

Designing a Successful Air and Water-Resistive System

An air and water-resistive system includes several building enclosure components. The success of the air and water barrier system depends on the input of the entire project team in the overall system design and execution. Specifying and installing air and water-resistive barrier membranes and accessories from a single manufacturer can improve continuity between materials and assemblies, limit supply chain issues, and allow for single-source warranties.

Tips for best practices when designing a continuous air and water-resistant barrier include:

Engage an air barrier specialist to review construction drawings and specifications during the design phase of the project to support the design vision and reduce the risk of errors or omissions concerning the air and water barrier system.

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WALLcontrol Polyiso Glass-Faced Insulation Board

When combined with quality exterior continuous insulation the design and attachment of the insulation should support the optimum performance of the air and water barrier.

If a vapor barrier is required by code, incorporate a vapor control layer in the design in a manner that facilitates drying in at least one direction of the wall assembly and in conjunction with an air barrier that prevents condensation that can result from air leakage and potential re-entrant air intrusion.

Installation of WALLcontrol Reinforced Aluminum AWB

Construct mockups (freestanding mock wall assemblies) that include the exterior wall substrate, air and water-resistive barrier system, with cladding, insulation, and fenestration installed to verify air tightness.

Man in yellow coveralls holding a roller and inspecting a gray wall

Conduct water and air leakage testing, identify deficiencies, and make repairs as needed to the air and water-resistant barrier systems before the final installation of cladding.

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Types of Air and Water-Resistive Barriers

Manufacturers of commercial air and water-resistive barriers typically offer two core material types: self-adhered sheets or fluid-applied membranes. Both of these membrane types have significant advantages over mechanically attached membranes. It is not uncommon to use both types of membranes on the same project to employ their unique advantages. For instance, self-adhered sheet membranes are often applied to long, opaque sections of a wall assembly, while fluid-applied membranes are ideal for the more difficult-to-cover areas such as curved surfaces, openings or corners, including areas of the building with complex geometries.

Choosing the right air and water barrier for the project depends on the budget, material costs, and the installer’s skills and familiarity with the product. The type of air and water-resistive barrier membrane specified and installed on a structure also must meet the designer’s and building owner’s performance expectations and specifications.

Self-Adhered Air and Water-Resistive Barrier

Self-adhered air and water-resistive barriers create a monolithic, waterproof, airtight layer when properly installed. These membrane types typically come in rolls and are composed of an engineered top sheet on the exterior side and an adhesive with release film underneath. Ideally, the self-adhered membrane utilizes a butyl adhesive for ultimate adhesion and temperature-stable performance properties. To properly install barriers over sheathing material, self-adhered air and water barriers may require a primer to obtain optimum adhesion.

Roller application of WALLcontrol Reinforced Aluminum AWB

Advantages of Self-Adhered Sheet Air Barriers

Some top sheets are engineered to be highly heat-stable
Accepts a wide range of adhesives and sealants
Durable enough to withstand the rigors of the construction process
Manufacturer-controlled membrane thickness
No mixing or special installation equipment needed
Bridges gaps easily without additional detailing
Allows for application in temperatures down to 20⁰ F (-6.6C)
No VOC’s

Fluid-Applied Air and Water-Resistive Barriers

Fluid-applied AWBs provide seamless, monolithic durable membranes that are fully adhered to the exterior sheathing without fasteners or priming. Installers can apply the membrane in one of three ways: spray, roll, or trowel the air barrier to the substrate. Fluid-applied AWB technologies include water-based acrylics and emulsions, solvent-based asphaltic, and moisture-cured silicone, such as STPE.

Spray application of WALLcontrol STPE AWB

Advantages of Fluid-Applied Air Barriers

Provides a seamless, monolithic, durable membrane
Excellent for complex geometries and rough surfaces
Easily seals around penetrations
High-solids STPE moisture-cure technology:
- Relatively quick cure time vs other technology fluid-applied air barriers
- Resists wash-off from rain, post application
- Maintains the original application thickness when cured
- Improves onsite installation reliability

Air and Water-Resistive Barrier Systems