How Does an Air Barrier Work?


For this week’s blog post, we discuss what an air barrier is and how it works. An air barrier is a material or group of materials that work alone or together to prevent air passage (e.g. air leakage from inside to outside and vise-versa) in excess of an established threshold through joints, seems, and holes in an exterior wall or roof assembly. The recognized air leakage rate threshold for an air barrier material and wall assembly are determined by ASTM testing.

Pecora offers several components that make up a four-step approach to a complete air & vapor barrier protection for your building envelope, plus an additional alternative product to XL-Flash. These components include Pecora XL-Flash, Fluid-Applied Resistive Barrer (XL-Perm ULTRA VP, XL-Perm ULTRA NP, or ProPerm VP – depending on the needs of the project), Pecora AVB Silicone Sealant, and Pecora XL-SPAN. An alternative product to XL-Flash includes Pecora XL-Wrap Thru Wall Flashing and Pecora XL-WraPrime Primer.

One of the components that make up the four-step approach to a complete air & vapor barrier protection for your building envelope is Pecora XL-Flash. XL-Flash is a unique semi-permeable, one-part, fast curing, non-sag elastomeric STPU (silyl terminated polyurethane) gun grade, trowelable liquid flashing & joint sealant. This product has many of the strengths of a two-component sealant but with the user-friendly ease-of-application properties of a one-component sealant. Pecora’s XL-Flash is specially formulated for the Air and Vapor Barrier Industry. It is resistant to ultra violet rays, ozone and airborne contaminants. It is designed to achieve high tensile and tear strengths, abrasion resistance and an average ultimate hardness of at least 55, yet still withstand 25% total joint movement. XL-Flash utilizes low VOC formulation that achieves primerless adhesion to most substrates.

The next component is a fluid-applied resistive barrier. Pecora currently offers three options: XL-Perm ULTRA VP, XL-Perm ULTRA NP, and ProPerm VP. Pecora XL-Perm ULTRA VP. XL-Perm ULTRA VP is a permeable, primerless, single component, high performance fluid applied STPU (Silyl Terminated Polyurethane) vapor retarding, water resistive air barrier coating that combines the best characteristics of silicone and urethane properties for exterior wall assemblies where it functions as an air and water barrier. It is resistant to ultra violet rays, ozone and airborne contaminants. Applied in a single coat via airless sprayer or roller, this durable elastomeric weatherproofing membrane provides two to three times the coverage of other fluid applied products. Pecora XL-Perm ULTRA VP has excellent elasticity and crack bridging capabilities contributing to a seamless durable airtight building envelope.

Pecora XL-Perm ULTRA NP is a non-permeable, primerless, single component, high performance fluid applied STPU (Silyl Terminated Polyurethane) that combines the best characteristics of silicone and urethane properties for exterior wall assemblies where it functions as an air, vapor and water barrier. It is resistant to ultra violet rays, ozone and airborne contaminants. Applied in a single coat via airless sprayer or roller, this durable elastomeric weatherproofing membrane provides two to three times the coverage of other fluid applied products. Pecora XL-Perm ULTRA NP has excellent elasticity and crack bridging capabilities contributing to a seamless durable airtight building envelope.

Pecora ProPerm VP is a single component, water based, permeable, primerless, fluid applied, cost effective, vapor retarding, water resistive air barrier membrane for exterior wall assemblies where it functions as an air and moisture vapor retarder. Applied with a roller or airless sprayer this elastomeric weatherproofing membrane provides superior protection from moisture vapor and air intrusion contributing to a seamless, durable, and airtight building envelope.

The third component is Pecora AVB. AVB is a single component 100% silicone sealant designed to adhere to low surface energy materials utilized in traditional and novel air and vapor barriers. Pecora AVB Silicone is designed as an integral component for transition seals between dissimilar materials in air and vapor barrier systems. Pecora AVB is also utilized as the adhesive for the Pecora XL-SPAN Pre-formed Silicone Transition Membrane.

The final component is Pecora XL-SPAN. XL-SPAN is a preformed silicone transition membrane used in combination with Pecora AVB Silicone Sealant/Adhesive to form an air and water tight barrier at transitions between building façade components such as fenestration products, roof to wall, internal expansion joints, and other openings in AVB and WRB systems. For use in cavity wall and curtain wall transition seals.

Our additional alternative product to XL-Flash is the Pecora XL-Wrap TWF. XL-Wrap TWF is a 45-mil cold applied, self-adhering membrane designed to act as a general purpose and thru wall flashing. The membrane is comprised of a durable cross laminated high-density polyethylene facer laminated to an exterior facing UV and weather resistant aluminum foil facer. XL-Wrap TWF utilizes a nonasphaltic, butyl-based adhesive that exhibits excellent adhesion and compatibility to a wide variety of building substrates. XL-Wrap TWF can be applied independently or as a component of the Pecora XL-Perm and ProPerm fluid applied air barrier systems.

Ultimately, the purpose of an air barrier system is to provide a continuous seal throughout the building’s envelope. This is achieved by ensuring all gaps and seams are caulked and sealed up tight. On any project, you are going to have multiple penetrations coming through your concrete wall or sheathing. These penetrations may include window openings, electrical boxes, seams in the sheathing, PVC piping, cables, conduit, etc. These penetrations need to be sealed in order to have a continuous seal. After these penetrations have been addressed, the fluid-applied resistive barrier can be installed to complete the continuous seal protection of the building.

To learn more about any of our air barrier products or for information on our air barrier application guide, please visit our website at https://www.pecora.com/air-vapor-water-barrier-products/. You can also reach out to one of our Technical Service Members by calling (800) 523-6688 or emailing at techservices@pecora.com.

One response to “How Does an Air Barrier Work?”

  1. From a Technical Sales perspective, the rate of repeat customers for these products including architects, general contractors and top quality applicators speaks volumes.

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