The History and Innovation of Weather-Resistant Substrates

architecture - engineering - construction

The History and Innovation of Weather-Resistant Substrates

April 24, 2019

Already effective in helping to reconstruct centuries-old European buildings, in 1969 exterior insulation and finish systems were introduced in the United States. Originally, when the oil crisis hit in 1976, the commercial building industry took a closer look at this energy-conscious option. But unlike Europe, substrates for in the U.S. contained organic wood-based fiber and gypsum sheathing was paper faced. These wood-based fiber substrates were prone to warping, swelling and susceptible to mold and rot. Their surface did not weather well, and some were not fire-resistant. By the early 1980s, EIFS commanded 25 percent of the commercial market in the U.S. but was in need of a stable substrate that weathered well during construction and was not moisture sensitive afterward.

In 1986, new fiberglass-mat gypsum sheathing—water resistant with low thermal and hydrometric expansion—was introduced. Unlike organic substrates or paper-faced gypsum sheathing, when fiberglass-faced gypsum sheathing was exposed to inclement weather for extended periods, it would perform well.

By the late 1990s, the manufacturers began developing EIFS with drainage, which included a . These systems, with WRB to prevent water penetration into the stud cavity, also helped maximize the life of exterior joint finishing materials. The 2006 IBC called for the addition of a WRB to address air and moisture issues over the surface of sheathing. To comply, architects, contractors and subcontractors needed a product that would minimize air leakage and moisture intrusion into the wall cavity. Glass-faced gypsum sheathing, which provides a stable base on which to apply the WRB, became a more compelling and popular option.

Gypsum Sheathing Evolves

During the past three decades, glass mat gypsum sheathing continued to evolve and National Gypsum developed the latest iteration which features sealed surface technology. SST provides a solid surface for the application of liquid-applied coatings and membranes, as well as traditional EIFS. By 2010, most manufacturers were producing glass mat gypsum with SST. Its weather-ability led to extended 12-month warranties, and allowed normal application rates of primers and water-resistive barrier coatings while providing better adhesion. And unlike earlier versions, the initial fiberglass “itch factor” that irritated construction workers on the jobsite was all but eliminated in the latest generation of gypsum sheathing with SST.

Benefits of Gypsum Sheathing

Glass mat gypsum sheathing, such as Gold Bond eXP Sheathing, saves time, labor and material costs. Regardless of geographic region (and how brutal the winters may be), it can withstand any weather and allows contractors more flexibility in scheduling. With gypsum sheathing, building professionals could forgo figuring in a 20 to 30 percent replacement cost in materials. The installation contractor could leave this product exposed for 12 months with the security of a warranty against delamination. Easy to install, gypsum sheathing also provides contractors with added assurance against mold-related litigation, which translates to more potential savings.

Speed of installation is another major advantage gypsum sheathing provides. A crew can work inside the building prior to the EIFS finish being put on the outside. Installation contractors no longer have to tear apart portions of a project due to weather-damaged materials. With glass mat sheathing, they can treat the joints, minimizing the possibility of moisture intrusion that can cause damage to other products while the building is under construction. This also reduces the required time for manpower on the job.

General contractors, responsible for the finished product, have additional peace of mind. They assume less liability. With glass-faced gypsum, there are extended warranties available for certain systems that are guaranteed for up to 10 years. Prior to gypsum sheathing, this kind of extended warranty did not exist.

Architectural Perspective

From an architect’s perspective, the reasons to specify it were multiplying as gypsum sheathing evolved. In 1991, when glass mat gypsum sheathing received its own classification of ASTM C1177, the numerical differentiation between this sheathing and other paper-faced sheathing (ASTM C1396) validated that it was in a distinct category and essentially a new product. It was moisture and fire-resistant, with enhanced strength provided by embedded reinforcing glass fibers. And factoring in possible defect claims and insurance costs, the mold-resistant properties of gypsum sheathing were cost effective. For architects, this also meant there was now a new type of sheathing for liability-sensitive projects, such as health care and educational facilities. The cost to redo a project due to mold or paper delamination was eliminated.

Meeting Stringent Standards

To meet new standards for energy conservation, sustainability and LEED certifications, contractors and architects must have products they can rely upon to create effective EIFS assemblies. Incorporating gypsum sheathing helps support the strength, performance and longevity of their projects.

As additional and stricter codes have been implemented, glass mat gypsum sheathing meets or exceeds their requirements. This includes the aforementioned 2006 IBC building envelope code changes and WRB applications. Gypsum sheathing also meets the requirements of the 2009 and 2012 International Energy Conservation Code. These IECC updates address improving the efficiency of the thermal envelope and insulation for commercial buildings. Continuous insulation was now required for a wall assembly in both stud cavity insulation and in continuous exterior insulation. Glass mat gypsum sheathing provided a base to fully meet these new requirements. With the IBC and IECC changes, inorganic glass mat gypsum sheathing helped to address energy code issues regardless of climate zone.

There are also the updated ASHRAE standards that demand continuous insulation outside the building along with fully adhered WRBs. To address these issues, as well as new sustainability standards and certifications, contractors and architects must design and build better high-performance assemblies. This now includes incorporating glass-faced gypsum sheathing into their projects.

Looking Forward

As requirements expand for air, water and insulation barriers and the need for dimensional stability increases, glass mat gypsum sheathing will become an even heavier-lifting building component. This sheathing has the ability to withstand weather exposure with a guaranteed warranty, to provide time and cost savings, to offer flexibility of design and ease of installation, and it has proven to provide dimensional stability in high-performance energy systems. It is a reliable substrate to utilize moving forward in the building industry, and will continue to outperform other substrate options in its ability to resist moisture, mold and fire.

Weather-resistant substrate originally developed for exterior insulation and finish systems.

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Company: National Gypsum