Masonry fireplace and chimney requirements per IBC 2113 and IRC R1003. Firebox: minimum 20 inches deep. Lining: firebrick minimum 2 inches thick laid in refractory mortar. Throat: minimum 8 inches above firebox, damper full width. Flue: clay flue liner (ASTM C315) or stainless steel liner. Size per Table R1003.1 based on fireplace opening. Chimney: minimum 3-5/8 inch nominal brick with flue liner, OR reinforced concrete minimum 4 inches. Height: minimum 3 feet above roof penetration, 2 feet above anything within 10 feet horizontally. Clearance to combustibles: minimum 2 inches all sides. Cricket/saddle: required on upslope side when chimney is wider than 30 inches. Spark arrestor: required in many jurisdictions (especially wildfire zones). Seismic: in SDC D/E/F, chimney must be reinforced with minimum 4 #4 vertical bars and #3 horizontal ties at 18-inch intervals, fully grouted.