Comparing Type X vs. Type C gypsum board
Understand the terminology for gypsum board use in fire-rated assemblies
Fire-rated assemblies constructed with gypsum board or drywall are a key component to ensuring life safety and complying with applicable building codes in both residential and commercial construction. The gypsum board used in fire-rated assemblies is usually described as either Type X or Type C. As a result, understanding the differences between these terms will aid in the selection of the correct product for use in each specific fire-rated assembly.
National Gypsum Company, through its affiliate company Gold Bond Building Products, LLC, provides more than two dozen Type X and Type C drywall products to meet a variety of requirements in addition to fire ratings, such as resistance to mold, moisture, sound, abuse, impact and weather exposure.
What is Type X drywall?
Type X gypsum board is defined by ASTM C1396 Standard Specification for Gypsum Board and has a different definition for each board thickness: 1/2", 5/8" and 1" thick.
Specifically, 1" thick shaftliner panels that qualify as Type X provide a 2-hour fire rating when installed in a double-layer, non-load bearing H-stud Area Separation Wall assembly. All gypsum shaftliner panels on the market meet this definition, so this article will focus only on 1/2" and 5/8" thick products.
A 5/8" Type X gypsum board is basically defined as a 5/8" gypsum board that will provide a 1-hour fire rating when a panel is applied to each side of a wood studs.
The full definition of Type X also requires that the studs be load-bearing 2x4 studs spaced 16" o.c. and the board be applied vertically with 6d nails spaced 7" o.c. with board joints centered over the studs and staggered on each side with fasteners spotted and joints covered with tape and compound. (See image below.)
A 5/8" Type X gypsum board is commonly used in 1- and 2-hour wood stud wall assemblies (UL designs U305 and U301) and 1-, 2-, 3- and 4-hour steel stud wall assemblies with one layer on each side for each hour of fire-resistance (UL design V438).
Variations in Type X gypsum board
In addition to 5/8" Gold Bond® Fire-Shield® Gypsum Board, Gold Bond Building Products manufactures many Type X varieties, including:
- 5/8" Gold Bond® XP® Fire-Shield® Gypsum Board: A mold-, mildew- and moisture-resistant Type X gypsum board for use in areas exposed to intermittent moisture such as behind toilets and sinks and as an exterior soffit board.
- 5/8" Gold Bond® SoundBreak® XP Wall® Board: A mold-, mildew- and moisture-resistant Type X gypsum board used to reduce sound transmission between rooms.
- 5/8" Gold Bond® XP® Hi-Impact® Gypsum Board: A mold-, mildew- and moisture-resistant Type X gypsum board for areas prone to cavity penetration.
- 5/8" Gold Bond® eXP® Interior Extreme® Gypsum Panel: A mold-, mildew- and moisture-resistant Type X gypsum board with glass-mat facers for pre-rock applications before the building is enclosed.
- 5/8" Gold Bond® eXP® Fire-Shield® Sheathing: A mold-, mildew- and moisture-resistant Type X gypsum board for use on exterior walls as a substrate for various weather barriers and cladding systems.
- 5/8" Gold Bond® eXP® Fire-Shield® Tile Backer: A code-compliant substrate for tile and other finishes in both wet and non-wet areas, high humidity areas and fire-rated assemblies.
- 5/8" Gold Bond® Kal-Kore® Fire-Shield® Plaster Base: A Type X gypsum board for use as a substrate for veneer plaster systems.
The definition for 1/2" Type X gypsum board is the same as that for 5/8" thick, except the required fire rating is only 45 minutes. Because model building codes require a minimum of 1 hour for most fire-rated construction, most drywall manufacturers do not provide a 1/2" thick Type X version of their 5/8" Type X product. Specifications for 1/2" Type X gypsum board will almost always require a Type C product.
What is Type C drywall?
Unlike Type X drywall, Type C gypsum board is not defined by any ASTM standard. Type C products are merely Type X products with special additives and have a “C” in their trade names to designate they have increased fire-resistance.
All 5/8" Type C products meet the ASTM definition for 5/8" Type X (1 hour), while all 1/2" Type C products meet the definition for 1/2" Type X (45 minutes). Consequently, all Type Cs are Type Xs, but not all Type Xs are Type Cs.
All manufacturers use the Type C designation though it has no technical definition.
Type C gypsum board was developed as an enhanced Type X to reduce the number of layers of standard Type X gypsum board required in multilayered, fire-rated assemblies. Type C is most often used in horizontal applications, including roof-ceiling, floor-ceiling and horizontal shaftwall assemblies.
In wood frame construction, for example, floor-ceiling assemblies have traditionally been constructed with two layers of 5/8" Type X as the ceiling membrane to provide a 1-hour fire rating. However, with the use of resilient channels and Type C gypsum board, only one layer is required. (See UL designs M563, L558 and P533 for examples of wood-framed floor-ceiling and roof-ceiling assemblies using RC-1 and Type C gypsum board.)
In wall assemblies, the use of Type C drywall will not reduce the number of layers but can reduce the overall thickness of the wall. A 2-hour wall can be achieved with either two layers of 5/8" Type X or two layers of 1/2" Type C on each side of metal studs, for example, but the use of 5/8” Type C in wall assemblies is uncommon.
Variations in Type C gypsum board
National Gypsum provides several varieties of Type C gypsum board, including:
- 5/8" Gold Bond® Fire-Shield C™ Gypsum Board: An enhanced Type X gypsum board with increased fire-resistance than standard Type X.
- 5/8" Gold Bond® Kal-Kore® Fire-Shield C™ Plaster Base: An enhanced Type X gypsum board used as a substrate for veneer plaster.
- 5/8" Gold Bond® XP® Fire-Shield C™ Gypsum Board: A specially formulated Type X gypsum board with mold-, mildew- and moisture-resistance ideal for painted exterior soffits.
- 5/8" Gold Bond® eXP® Interior Extreme® Fire-Shield C™ Gypsum Panel: A mold-, mildew- and moisture-resistant, enhanced Type X gypsum panel with glass-mat facers for installations before the building is enclosed.
Lightweight Type X drywall products
Lightweight Type X gypsum board products are relatively new to the construction industry and blur the line between Type X and Type C. As Type X products, they are included in most fire-rated wall designs but are also permitted in many floor-ceiling and roof-ceiling assemblies that require Type C products. For example, 5/8" Gold Bond® High Strength Fire-Shield 60® Gypsum Board is specially formulated to be 20% lighter than standard Type X gypsum board and can be used in UL designs M563, L558, and P533 for wood framed floor-ceiling and roof-ceiling assemblies.
How to avoid costly errors during construction
A common question to the 1-800-NATIONAL® Construction Services department is as follows:
“The contractor installs 5/8" Type X gypsum board on the ceilings as specified in the construction documents. A building inspector later points out that the UL design requires a Fire-Shield C gypsum board. Who is correct?”
The answer is: Everybody. Architectural drawings typically label gypsum board in fire-rated assemblies generically as Type X, even though not all Type X products will comply. It is important to consult the UL design or GA file number for the specific Type X product required, because it may be a Type C.
The important thing to remember is that most wall assemblies allow 5/8" Type X products and do not require Type C (though Type C is permitted), but most floor-ceiling and roof-ceiling assemblies will require either 1/2" Type C or 5/8" Type C products.
How are Type X and Type C products specified in fire-rated assemblies?
The fire-rated assemblies found in the Gypsum Association GA-600 Fire Resistance and Sound Control Design Manual specify generic or proprietary 1/2" Type X and 5/8" Type X products. They do not reference Type C because, again, Type C has no technical definition.
For generic designs specifying 1/2" Type X gypsum board, 1/2" Fire-Shield C, 1/2" XP Fire-Shield C, or ½” eXP Interior Extreme Fire-Shield Type C is required. For generic 5/8" Type X designs, both 5/8" Fire-Shield, XP Fire-Shield and eXP Interior Extreme Type X and Type C would be permitted. Proprietary designs for both 1/2" or 5/8" products will specify the individual products by their exact trade names.
UL designs do not reference Type X or Type C products at all. All UL designs will specify products by their individual product designation (a short code assigned to each product and listed on the individual product submittal), or they will have the following sentence:
- Gypsum Board* — Any 5/8" thick UL Classified Gypsum Board that is eligible for use in Design Nos. L501, G512 or U305.
UL design U305 is similar but slightly more stringent than the ASTM definition for 5/8" Type X and lists all 5/8" Type X products by all manufacturers. Therefore, any UL design with this sentence allows all Type X products without using the term “Type X.”
Need additional support? Contact the technical experts on National Gypsum’s Construction Services team at 1-800-NATIONAL.
