Section R503 addresses roof coverings used in residential construction. Asphalt shingles are the most common residential roofing material, with Class A fire-rating achieved through mineral coating on the asphalt surface. Wind resistance ratings include basic (50 mph), high-wind (90 mph), and extra-strength ratings. Underlayment below shingles protects the deck from water infiltration if shingles are blown off or during installation. Ice and water barriers in cold climates prevent water backup from ice dam formation. Roof-to-wall flashing transitions prevent water from running down walls. Valley flashing (where two roof slopes meet) directs water down the slope. Penetration flashing around chimneys, pipes, and vents prevents water leakage. Metal roofing is also permitted with proper fastening and sealing. Wood shingles and shakes are permitted but require fire-resistant treatment. Tile and slate roofing is permitted and is durable but expensive. Roof ventilation in cold climates requires soffit intake and gable or ridge exhaust to prevent moisture condensation.