Whats the difference between “regular” and “type X” gypsum wallboard?
ASTM C 36 designates two types of gypsum wallboard, regular and type X. Type X wallboard, which is typically required to achieve fire resistance ratings, is formulated by adding noncombustible fibers to the gypsum. These fibers help maintain the integrity of the core as shrinkage occurs, providing greater resistance to heat transfer during fire exposure. To receive the “Type X” designation under ASTM C 36, a gypsum wallboard product must be shown to achieve not less than a one hour fire resistance rating for 5/8″ board or a 3/4 hour fire resistance rating for 1/2″ board applied in a single layer, nailed on each face of load-bearing wood framing members, when tested in accordance with the requirements of ASTM E 119, Methods of Fire Test of Building Constructions and materials. Additionally, the Gypsum Association requires 1/2″ type X gypsum board be shown to achieve a one hour fire resistance rating when applied to a floor ceiling system, as described by GA File Number FC 5410, in GA 60