One layer 5/8” (15.9 mm) ToughRock® Fireguard C® gypsum board or 5/8” (15.9 mm) DensArmor Plus® Fireguard C® interior panels applied to resilient or rigid furring channels with 1” (25.4 mm) Type S drywall screws 12” (305 mm) o.c. Channels spaced 12” (305 mm) o.c. when insulation is used or 16” (406 mm) o.c. when no insulation is used. Resilient channels applied perpendicular to bottom chord of pitched or parallel chord steel trusses 48” o.c. with 1/2” (12.7 mm) Type S-12 screws. Optional glass fiber or mineral fiber batt or loose fill insulation applied directly over ToughRock Fireguard C gypsum board only. Trusses supporting metal roof deck panels covered by 1/2” (12.7 mm) regular gypsum sheathing either loose laid, or adhesively or mechanically attached to roof deck. Any thickness polyisocyanurate foamed plastic; polystyrene foamed plastic; or mineral fiber or glass fiber insulation boards laid over gypsum sheathing and covered by a Class A, B or C roof covering.