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.) and ULC (Underwriters’ Laboratories of Canada) to meet the fire performance requirements prescribed in the ASTM C1396 (CAN/CSA-A82.27) Standard Specification for Gypsum Board.
Type X fire rated gypsum drywall that is 5/8 -inch (15.9mm) thick and installed on each side of nominal 2-inch x 4-inch (38x89mm) wood studs spaced 16-inch (400mm) o.c. or 3-5/8 inch (610 mm) steel studs spaced 24” o.c. has a minimum fire rating for the assembly of 1 hour, which is a typical requirement for many building codes.
Type C fire rated drywall (sometimes referred to as Improved Type X) 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 (12.7 mm) and 5/8-inch (15.9mm) thicknesses.
Fire rated Type X Shaftliner is 1” (25.4 mm) thick and used in special Shaftwall and Area Separation Firewall assemblies.
In residential homes, installation of fire rated drywall is often required by state/province 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. Fire rated drywall is typically found on attached garage walls and ceilings that are adjacent to the main living area of the home.
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.