A roof deck is the structural surface installed over roof framing (rafters or trusses) that provides the base for roofing materials. Common roof deck materials include plywood, oriented strand board (OSB), or wood planks. The deck must be properly installed and in good condition to support roofing materials and resist weather. Building inspectors check roof deck installation before roofing proceeds. Roof deck also refers to flat roof surfaces used as outdoor living spaces—rooftop patios or terraces. Building codes address both structural roof decks and accessible rooftop decks, specifying materials, waterproofing, drainage, and safety requirements like railings and weight capacity.