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Understanding the UL Directory:
Fire-Resistant Assemblies
Creating Code-Compliant Designs
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Advertising supplement provided by
National Gypsum Company

Which Type of Drywall Is Most Fire Resistant?

There are three essential core types. Drywall comes in regular core, Type X and Type C. All drywall affords some degree of fire protection. After all, it’s rock, it’s water, it’s difficult to burn. Regular drywall is fire resistant. It’s composed mainly of gypsum. Type X drywall contains additional ingredients that enhance its fire-resistive properties. The basic component added to Type X to give it superior resistance is fiberglass. Finally, systems tested in the laboratory utilizing Type C gypsum wallboard are the most fire resistant. The make-up of Type C drywall is, generally, proprietary, but its fire resistive properties are superior to Type X.

The most important characteristic of drywall, say fire officials, is that it will not burn. “Statistics show that in recent years, fewer people have died in fires in the U.S.,” says the Gypsum Association. “Naturally, there is no single reason for the decline. But the diminished number has a high correlation with the increased use of gypsum products and other fire-resistant building materials,” they say.

“The gypsum in the core of the board actually emits steam when exposed to fire and retards transfer through the panel. This slowdown provides extra time to evacuate a room or building.”

“Ask yourself this question, says Piccolo: ‘How do I know what type of drywall is being installed? Is it regular drywall, Type X, or Type C? The drywall will be stamped if it is Type X or Type C.’ The UL stamp on the back of the gypsum wallboard Advises you if the board is Type X or Type C in addition to letting you know that the wall board is consistent in its construction, that you have quality, and performance. Since the stamp will be on the back of the drywall, you will have to inspect it prior to completion of the assembly.”

Navigating the UL Directory

Specification of fire-resistant gypsum systems starts at the UL home page and becomes a relatively simple, essentially cut-and-paste, web-based exercise that eliminates oversight and provides the contractor with a detailed wall, ceiling or floor configuration.

On the left-hand side of the UL home page (

  • Click on “Certification.”
  • Click on “Fire-Resistive Assemblies and Systems.”
  • Click on “Numbering System for Fire Rated Assemblies.”

Up comes a chart of fire-rated assemblies that becomes your numeric guide to detailed specifications for walls, ceilings and floor systems (Figure 3).

Figure 3

You will learn how to select a numeric code that relates to the project detail in question by doing an exercise later in this article. When the results page comes up, click in the box under ‘Link To File’ column to view design detail.

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