Hearth and Hearth Extensions FYI
A fireplace hearth is the floor area within a fireplace. It is made from noncombustible materials, such as brick or stone.
The fireplace hearth and hearth extension is the noncombustible material in front of and at the sides of a fireplace opening. Fireplace hearths and hearth extensions are designed to prevent sparks from leaving the fireplace and igniting nearby combustibles. Your fireplace design ideas should have these very important areas in mind.
Guidelines For Fireplace Hearths
Guidelines for sufficient thickness and size of fireplace hearths and fireplace hearth extensions can be found in the International Phase I Standards of Practice for Inspecting Fireplaces and Chimneys and in the manufacturer’s instructions. Fireplace hearths are very much an issue with your fireplace design ideas so understanding these requirements are essential:
The following is from the International Phase I Standards of Practice for Inspecting Fireplaces and Chimneys:
The inspector should inspect for a hearth extension that has a thickness of less than 2 inches.
The inspector should inspect for a hearth extension that is less than 16 inches in front or less than 8 inches beyond each side of fireplace openings (6 square feet or less).
The inspector should inspect for fireplace hearth extensions that are less than 20 inches in front or less than 12 inches beyond each side of fireplace openings (greater than 6 square feet).
The inspector should inspect the fireplace hearth, hearth extensions, and chambers for joint separation, damage and deterioration.
The 2006 International Residential Code (IRC) offers the following exception to the 2 inch-thick rule:
When the bottom of the firebox opening is raised at least 8 inches (203 mm) above the top of the hearth extension, a hearth extension of not less than 3/8-inch thick (10 mm) brick, concrete, stone, tile, or other approved noncombustible material is permitted.