Case study
The integrated sheathing addressed the majority of the concerns mentioned earlier with one product and limited trips around the building to install it. The selected wall assembly incorporated a gypsum-integrated WRB-AB sheathing matched with a liquid flashing approved for damp conditions, which sealed the joints, seams, corners, and penetrations. Altogether, this installation created a hydrophobic, monolithic surface to block bulk water, and an airtight building enclosure to achieve energy-efficiency goals, all while allowing for vapour permeability and effective drying and providing fire resistance, as required by the National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components.
With barrier layers fully sealed, the construction team turned its attention to the exterior cladding and aesthetic of the building. The Benoit Farms project in Hayesville, N.C., called for a layer of ci to achieve its energy-efficiency goals. On top of that, the project called for 20-gauge corrugated steel cladding on the residential building and one barn, and 14-gauge steel on another barn. The cladding was attached to 20-gauge hat channels and secured through the ci and into 18-gauge metal framing with long roofing screws. Behind the scenes, the gypsum-integrated sheathing provided the air and water barrier, while serving as a rigid substrate for the insulation, and offering structural integrity in the way of shear strength for the wall assembly.
Climate and insulation considerations
Two schools of thought exist around keeping moisture out of buildings, recognizing cladding as the first line of defence. One approach favours wall assemblies—including cladding selection and installation techniques—designed to keep water out altogether. The other method acknowledges water infiltration in some form and quantity is inevitable, and effective moisture management is more important than keeping water out in the first place.
As discussed, many popular cladding options are susceptible to moisture, making the second approach a logical one for commercial builders. So, assuming some water is bound to get behind the cladding, gypsum sheathing is a suitable starting point. All gypsum sheathing is vapour permeable and has the capacity to retain its integrity even as it moves through wetting and drying cycles. In selecting a gypsum-integrated WRB-AB sheathing, designers benefit from this quality, as well as the consistency of a known permeability level that will not be changed by the addition of separate control layers. For example, an integrated sheathing rated at 25 perms will retain that rating on installation because it already accounts for the permeability of the WRB-AB. This is in contrast to a non-integrated sheathing whose permeability changes depending on the control layers applied.
However, the issue is complicated by the widespread use of continuous insulation code requirements on commercial buildings. Depending on the type of insulation and its installation—directly up against the WRB-AB layer, or within the cladding installation framing—the location of the drainage plane and drying capabilities of the wall assembly may change.
For example, in a cold climate, designers may choose an integrated WRB-AB sheathing, followed by mineral wool ci, and an air gap between the insulation and their cladding of choice. This wall assembly should dry well to the outside with the cladding spaced off insulation. However, if a foil-faced polyisocyanurate (ISO) ci is used, it would not dry well to the outside. Pressed up against the WRB-AB layer, the ISO would stop movement of moisture at its surface, and designers would have to provide a drainage cavity.
With the thermal control and moisture management requirements of wall assemblies varying by region, designers should remove as many complications as possible from the design and construction 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 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 building’s 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.
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 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 wall assembly includes a combustible component, then a test or engineering judgement is necessary. If all components of the assembly are noncombustible, then testing is unnecessary.
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.
