UL Design P522

1-Hour Fire Rated P522 assembly

UL Design P522 — One-hour wood truss roof-ceiling (unrestrained assembly rating 1 hr; finish rating 25 minutes with specific insulation configurations). Pitched or parallel-chord wood trusses fabricated from nominal 2x4 lumber, spaced max 24 in. o.c. (min 18 in. depth for parallel-chord trusses), carry a nominal 15/32 in. wood structural panel roof deck secured with 6d ringed-shank nails 12 in. o.c. The ceiling is one layer of nominal 5/8 in. Type X gypsum board, 48 in. wide, installed with the long dimension parallel to trusses on resilient channels of 25 MSG galvanized steel run perpendicular to the trusses, spaced max 16 in. o.c. without insulation or 12 in. o.c. with insulation. Insulation options include glass fiber batts (min 0.5 pcf), spray-applied cellulose (min 0.5 pcf), or spray foam (0.5-2.5 pcf, up to 17 in. depending on product).