Gypsum is approximately 21 percent by weight chemically combined water which greatly contributes to its effectiveness as a fire resistive barrier. When gypsum drywall is exposed to fire, the water is slowly released as steam, effectively retarding heat transmission.
Fire rated gypsum drywall is more fire resistant because it contains glass fiber reinforcement and other additives within its specially formulated gypsum core to help it hold up longer to a fire exposure.
Fire rated drywall is referred to as “Type X” and must be third-party certified by an independent testing and listing agency such as UL (Underwriters Laboratories Inc.) to meet the fire performance requirements prescribed in the ASTM C 1396 standard specification for gypsum board products.
Type “X” fire rated gypsum drywall that is 5/8 -inch thick and installed on each side of nominal 2-inch x 4-inch wood studs spaced 16-inch o.c. or 3-5/8 inch steel studs spaced 24” o.c. has a minimum fire rating for the assembly of 1 hour, which is a typical requirement for most building codes.
Type “C” fire rated drywall is similar in composition to Type X, except that it has more glass fiber reinforcement and other ingredients in the gypsum core that makes its fire resistive properties superior to Type X. Type C gypsum board is available in 1/2-inch and 5/8-inch thicknesses.For commercial buildings, fire rated gypsum drywall is specified for most of the building walls and ceilings to meet building code requirements for fire partitions and assemblies. These fire rated partitions and assemblies provide life safety for the buildings occupants.
In residential homes, installation of fire rated drywall is required by state and local building codes on interior and exterior walls near furnaces and utility rooms. Fire rated drywall can also be installed in a basement or other places where a wood stove might be used or around the opening of a fireplace. Fire rated drywall is typically found on garage walls and ceilings that are adjacent to the main living area of the home.