Basics of Fire-Rated Type X or C Drywall

When you are installing drywall, building code often dictates the types of drywall that must be used. One type of drywall that shows up in building codes is Type X or Type C drywall or fire-rated drywall.

While beneficial, fire-rated drywall is often given more attributes than it truly has. This drywall is fire-rated but not fireproof. While it will slow down the passage of fire, it will not stop it. Type X or Type C drywall is only one of many methods homeowners should use to stay safe in the event of a home fire. In fact, fire ratings for Type X or C drywall can be a bit deceptive because they refer to full, complete wall system, not just the drywall.

What Is Fire-Rated Type X Drywall?

Fireproof drywall is the common term; its industry name is Type X drywall. The thickness of this drywall is 5/8-inch, including all layers.

Glass fibers are added to the board to help it slow down the fire. Also, because it is denser than normal gypsum and paper drywall, it takes longer for the fire to degrade it.

Most Type X drywall has a one-hour fire rating. The fire rating for the 1/2-inch drywall used throughout the rest of the home is 30 minutes.

As an added benefit, Type X drywall absorbs sound slightly better and is slightly stronger than conventional 3/8-inch or 1/2-inch drywall.

Type X vs. Type C Drywall

Both Type X and Type C drywall are rated as fire-resistant materials. Both have 60-minute wall system ratings.

Type C has more additives to the gypsum core that make it slightly more fire-resistant than Type X drywall.

Why Fireproof Drywall Is Fire-Rated

Type X or C drywall is by no means 100-percent fireproof. Simply it is drywall that will stand up against flame longer than regular drywall.

Also, just because an area is covered in Type X or C drywall does not ensure fire safety for that area, since fire can still find other pathways, such as vents, doors, gaps, cracks, and unblocked stud wall assemblies.

If a conventional 1/2-inch thick sheet of drywall will stand up to 30 minutes of fire, then the added 1/8-inch found in the Type X or C drywall, along with its other properties, will double your margin of safety to 60 minutes. For this reason, fire-rated drywall is sometimes called one-hour fire wallboard.

Where to Install Type X or C Drywall

In residences, fire-rated drywall is typically required by building codes to be installed in a few of these places:

• Near furnace and utility rooms
• Places where a wood stove is used
• Garages and especially the garage walls that separate that area from the main house
• Garage ceilings that have living areas above

Should You Install Type X or C Drywall Everywhere?

No, fire-rated drywall is not intended to be installed in all areas of the home.

Fire-rated drywall tends to run about 20-percent more expensive than conventional drywall panels. While this is not much on the small scale, it can represent a substantial cost difference when multiplied across an entire home's worth of drywall.

More importantly, the fire will find any number of easier passages to travel than through drywall. For example, if a bathroom, nursery, bedroom, or home office were hung with Type X or C drywall, the fire would readily move through oxygen-rich open doors and hollow-core doors long before attempting to burn through the drywall.

If you want fire-rated drywall to be installed throughout your house, you would need to request this with the contractor, as this is not normally done.

Type X or C Drywall Testing Limitations

The ability of Type X or C has less to do with the actual drywall sheet and more to do with the entire wall system as a whole: all items included such as studs and insulation.

USG, the manufacturer of Sheetrock Brand Firecode C Gypsum Panels, makes the point that ASTM (American Society For Testing and Materials) testing of fire-rated drywall requires that entire "assembly/systems" be tested, not just the drywall.

Because these assemblies are composed of many different parts, any of which could affect results, these results may be skewed. USG notes:

This simply means that for a 'one-hour fire rating' of a gypsum board assembly/system, all requirements of an ASTM E 119 test were successfully met in a testing laboratory furnace for at least 59 minutes and 30 seconds for that specific assembly/system and with those specific components of the assembly/system.

Thickness and Composition

Drywall typically comes in 1/4-inch, 3/8-inch, and 1/2-inch thicknesses. Type X or C drywall is 5/8 inches thick.

In addition to the usual gypsum found in regular drywall, fire-rated drywall contains glass fibers to form a super-tough core. The gypsum and fiberglass are packed tighter and denser than with regular drywall.

Cost and Availability

Fire-rated drywall costs more than regular drywall. As a rule of thumb, you can count on it costing about 10-percent to 20-percent more than conventional drywall of the closest possible thickness.

Type X or C fire-rated drywall is not a specialty product. It is available at local home improvement stores or contractors' supply houses.