Two layers 1” (25.4 mm) ToughRock Shaftliner or DensGlass® Shaftliner inserted in H-Studs 24” (610 mm) o.c. Min. 3/4” (19 mm) air space on both sides must be maintained between liner panels and adjacent framing. Sound Tested with 2”x 4” stud wall with 1/2” (12.7 mm) ToughRock® Fireguard C gypsum wallboard or DensArmor Plus® Fireguard C panels each side of assembly and 3-1/2” (89 mm) fiberglass insulation in stud space both sides. Breakaway clip facings and height of wall differ between UL Design U373 and WHI GP/WA 120-04. Please consult each listing for specific information.