Exterior: Two layers 5/8” (15.9 mm) DensGlass® Fireguard Sheathing applied vertically or horizontally to 2 x 4 wood studs 16” (406 mm) o.c. Base layer attached with 1-7/8” (48 mm) galvanized roofing nails 16” (406 mm) o.c. Face layer attached with 2-3/8” (60 mm) galvanized roofing nails 8” (203 mm) o.c. Stagger joints between layers and on base layer of both sides. Interior: Two layers 5/8” (15.9 mm) DensArmor Plus® Fireguard® or 5/8” (15.9 mm) ToughRock® Fireguard X® applied horizontally or vertically to framing. Base layer attached with 1-7/8” (48 mm) 6d cement coated nails 6” (152 mm) o.c. Face layer attached with 2-3/8” (60 mm) 6d cement coated nails 8” (203 mm) o.c. Stagger joints between layers and on base layer of both sides. Sound tested with studs 16” (406 mm) o.c. and nails for base layer spaced 6” (152 mm) o.c.