All the mantels on this web site will meet building codes in most areas of the United States, it is the customer's responsibility to contact their local building code authority to determine if the the mantel opening fits the local building code. If there is no code for mantel openings in relation to firebox openings in your particular area, we strongly suggest the mantel and firebox meet the National Building Code. The following is a reprint from the Standard Building Code.

2114.3 MASONRY FIREPLACES
2114.36 Fireplace hearth extensions shall be of approved noncombustible materials for all fireplaces. Where the fireplace opening is less than 6 sq.ft. (0.56m²), the hearth extension shall extend at least 16 inches (406mm) in front of the facing material and at least 8 inches (203mm) beyond each side of fireplace opening. Where fireplace opening is 6 sq.ft. (0.56m²) or larger, the hearth extension shall extend at least 20 inches (508mm) in front of the facing materials and at least 12 inches (305mm) beyond each side of the fireplace opening. Where a fireplace is elevated above or overhangs a floor, the hearth extension shall also extend over the area under the fireplace.

2114.3.7 Fireplaces constructed of masonry or reinforced concrete shall have hearth extensions of brick, concrete, stone, tile, or other approved noncombustible material properly supported and with no combustible material against the underside thereof. Wooden form or centers used during the construction of a hearth and hearth extensions shall be removed when construction is completed.
EXCEPTION: A header of combustible material may be used to support the hearth extension provided that it is located more than 12 inches (305mm) from the face of the fireplace.

2114.3.8 All combustible wood beams, joist, and studs shall be maintained a minimum of 2 inches (51mm) from the outside face of the chimney or fireplace masonry. Headers supporting trimmer arches at fireplaces shall be not less than 20 inches (508mm) from the face of the chimney breast. Trimmers shall be not less than 6 inches (152mm) from the inside face of face of the nearest flue lining.

2114.3.9 Woodwork shall not be placed within 4 inches (102mm) of the back of the fireplace, but shall not prevent plastering directly on the masonry or metal lath and metal furring.

2114.3.10 All combustible mantels and similar trim shall be kept at least 6 inches from fireplace opening. Parts of the mantel assembly located along the sides of the fireplace opening, which project more than 1-1/2 inches (38mm) from the face of the fireplace, shall have additional clearance equal to he projection. Parts of the mantel assembly located above and projecting more than 1-1/2 inches (38mm) from the fireplace opening shall not be placed less than 12 inches (305mm) from the top of the fireplace opening.