hearth measurements

Old 01-19-03, 07:08 PM
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hearth measurements

Do you know the code measurements and materials for fireplace hearths? I have a 36" gas fireplace that I am refacing. Thank you!
Old 01-19-03, 08:23 PM
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R1003.9.1 Hearth Thickness - The minimum thickness of firepalce hearths shall be 4" thick. (102)

R1003.9.2 Hearth Extension Thickness - The minimum thickness of hearth extension shall be 2" (51 mm)

Exception; When the bottom of the firebox opening is raised at least 8" (203mm) above the top of the hearth extension, a hearth extension of not less than 3/8" inch thick (9.5mm) brick, concrete,stone, tile,or other approved noncombustible material is provided.

R1003.10 Hearth Extension Dimensions - Hearth extensions shall extend at least 16 inches (406mm) in front of and at least 8 inches (203mm) beyond each side of the fireplace opening. Where the fireplace opening is 6 square feet (0.557m2) or larger, the hearth extension shall extend at least 20 inches (508mm) in front of and at least 12 inches (305mm) beyond each side of fireplace opening.

R1003.12 Fireplace Clearance - All wood beams, joists, studs and other combustible material shall have a clearance of not less than 2 inches (51mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102mm) from the back of masonry fireplaces. The air space shall not be filled except to provide fireblocking in accordance with Section R 1003.14.


1. Masonry fireplaces listed and label for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufactures installation instructions are permitted to have combustible material in contact with their exterior surfaces.

2. When masonry fireplaces are part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (305mm) from the inside surface of the nearest firebox lining.

3. Exposed combustible trim and edges of sheathing materials such as wood siding, flooring and drywall shall be permitted to abut the masonry fireplace sidewalls and hearth extension provided such combustible trim or sheathing is a minimum of 12 inches (305mm) from the inside surface of the nearest firebox lining.

4. Exposed combustible mantels and trim may be placed directly on the masonry fireplace front surrounding the fireplace opening providing such combustible materials shall not be placed within 6 inches (152mm) of a fireplace opening. Combustible material within 12 inches (306mm) of the fireplace opening shall not project more than 1/8 inch (3.2mm) for each 1-inch (25.4mm) distance from such opening.

Just a note, your fireplace instructions may also have info on this if you have them.

Hope this helps! (wow, alot of typing!!)
Old 01-19-03, 08:36 PM
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If you have a dedicated gas fireplace (manufactured to only burn gas) like a direct vent or natural venting model, then a hearth is not required.

If you have a wood burning fireplace that has a gas line run to it, then see the guidelines from the previous post from Mr. Alshire

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