WRB-AB sheathing streamlines wall assembly and cladding compatibility

Architecture firm LG Squared attached integrated gypsum sheathing to the cladding of the Benoit Farms building in North Carolina to provide a continuous WRB-AB layer and protect the building and its occupants from potential fires.
Architecture firm LG Squared attached integrated gypsum sheathing to the cladding of the Benoit Farms building in North Carolina to provide a continuous WRB-AB layer and protect the building and its occupants from potential fires.

With the thermal control and moisture management requirements of wall assemblies varying by region, designers should remove as many complications as possible from the specification process. Gypsum-integrated WRB-AB sheathings achieve this uniform approach to moisture management, letting designers focus on the remaining building science requirements, regardless of the cladding.

Fire compliance achieved

The benefits of gypsum-integrated WRB-AB sheathing do not just stop at air and moisture protection and cladding compatibility. These materials also help buildings meet fire-safety standards.

WRBs, ABs, and ci are all intended to improve building performance. However, a renewed focus on exterior wall assemblies considers the propagation of fire due to the design and cladding materials. This issue was underscored by the 2017 Grenfell fire in London, United Kingdom. Specifically, authorities are enforcing code requirements of wall assemblies and compliance with NFPA 285 testing.

To meet the International Building Code (IBC) requirements for wall assembly fire performance, all WRBs must be in compliance with NFPA 285. Unlike systems comprising a primary WRB material and flashing accessories that are sometimes combustible, gypsum-integrated WRB-AB assemblies start with the fire-resistance of gypsum and typically incorporate noncombustible WRB sheathing with liquid flashing accessories. It is important designers who are creating wall assemblies with wood-based integrated sheathings, or integrated sheathings with a pre-cured liquid membrane on the surface, should recognize these are combustible materials and must find other ways to address fire-resistance requirements.

Some designers may wonder if all combinations of WRB/AB products and sheathing should be tested together to meet NFPA 285. Generally, if the exterior wall assembly includes a combustible component, then a test or engineering judgment is necessary. If all components of the specified assembly are noncombustible, then testing is unnecessary.

As of 2018, IBC updated its standard method for evaluating fire propagation characteristics for external wall assemblies. It specifies that NFPA 285 compliance testing criteria no longer considers WRB flashings or accessories to be part of the barrier, as they comprise such a small portion of the assembly. More to the point, this update separates multi-component assemblies into the primary WRB and accessories or flashing products. For example, a termination mastic on a self-adhered membrane system would be consider an accessory, while the membrane itself would be considered the primary WRB. With this in mind, sheathing made from fiberglass mat with a gypsum core—classified as a noncombustible WRB—is exempt from NFPA 285 assembly testing, and IBC 1402.5 requirements for combustible WRBs are inapplicable.

With that in mind, using an NFPA 285-approved WRB-AB sheathing simplifies the cladding process by bypassing the need for any additional testing specific to the barrier.

Give the design every advantage

As integrated WRB-AB sheathings increase in popularity, now is the time for architects and designers to give these materials a closer look. Why restrict cladding possibilities based on the parameters of inflexible multi-component barrier layer options? As an industry innovation, integral WRB-AB sheathing systems support cladding versatility and maintain fire and water-resistance compliance while simplifying wall assembly design and supporting efficient construction.

Broadening a world of design possibilities without the complication of individual component synergy eliminates the hassle of accounting for the differences across a variety of cladding and sheathing combinations. With gypsum-integrated WRB-AB sheathing, designers can accent the north-facing side of a building with brick, while styling the south in EIFS.

John Chamberlin is a senior product manager at Georgia-Pacific. He is responsible for the DensElement Barrier System and the DensDefy line of products. Chamberlin has worked in the building materials industry for his entire career, focusing on new product development for disruptive technologies in the building envelope space. Chamberlin is on the board of the Air Barrier Association of America (ABAA). He graduated from the University of Tennessee with a bachelor’s degree in marketing and later received his MBA from Emory University. He can be reached at john.chamberlin@gapac.com.

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