Fireplace Mantel Clearances

Knoji reviews products and up-and-coming brands we think you'll love. In certain cases, we may receive a commission from brands mentioned in our guides. Learn more.
How to determine the allowable clearance to combustible materials for a fireplace mantel and surround.

If you have a gas or wood-burning fireplace it is important that you understand the proper clearances to the fireplace mantel and surrounding materials. Combustible fireplace surrounds and mantels must be held back from the actual fireplace opening to minimize fire danger. Most fireplace surrounds are composed of several materials such as stone, tile, metal, and wood.

IRC Code

In the 2009 Edition of the IRC (International Residential Code) Section R1001.11 Exception 4: “Exposed combustible mantels or trim may be placed directly on the masonry fireplace front surrounding the fireplace opening providing such combustible materials are not placed within 6 in. of a fireplace opening. Combustible materials within 12 in. of a fireplace opening shall not project more than 1/8 in. for each 1-in. distance from such opening.”

However, state and local building codes and ordinances can vary from the IRC or may use standards from older versions of the same code. To ensure maximum safety, check with your local and state building ordinances before mounting a mantel.


The National Fire Protection Association (NFPA) has similar requirements as the 2009 IRC. The NFPA code states that any mantel must be at least 6 inches from the fireplace opening. In addition, any combustible trim elements measuring at least 1 1/2 inches thick must be at least 12 inches from the fireplace opening which is equivalent to the IRC ruling which requires 1 inch of distance for every 1/8 inch of projection. (12 x 1/8 = 1 ½ )

Both codes are silent about the permitted projection after 12 in. from the firebox.


You may need to consult your local building codes to determine which code the building department is following and if there are any additional requirements put forth by the fire department officials.

Full Masonry Constructed Fireplaces--These types of fireplaces are incorporated into an entire wall. These fireplaces need a minimum clearance of 12 inches from the sides and top from combustible materials to meet code requirements. These fireplaces are wood burning, custom-built fireplaces.

Prefabricated Fireplace Units--These units are constructed in the factory and are made of steel. These units can be wood burning, gas, or pellet burning. These fireplace units fall into the category of minimum clearance requirements, where air spaces on the sides and back can be as little as 1 inch. This allows air to circulate around the unit. Direct contact under UL127 is permitted with the metal trim on these units as long as the manufacturer’s installation instructions are followed exactly.

Decorative Masonry Fireplaces--Masonry fireplaces that have mantels that project, must extend no more than 1/8 inch for every inch of the distance to the mantel from the top of the firebox. This is also the distance the noncombustible surround must be on the top. For example, if the mantel sticks out 3 inches, the top of the surround should be 12 inches.

Surround Material Requirements

The surround must be made of noncombustible material around wood burning masonry fireplaces such as tile, concrete, stone, marble or granite. Prefabricated units must have a fireplace surround that complies with the manufacturer's recommendations and clearances. Some prefabricated units can have direct contact with combustible materials including wood. These units are usually wood burning units. Always follow the manufacturer's recommended clearances in the instruction manual.

It is important to remember the material used for the surround be noncombustible, but that the adhesive or fasteners also be noncombustible. Surround materials for some prefabricated units can be secured with screws. For masonry fireplaces where a noncombustible surround is needed, a noncombustible adhesive is also needed. Mortar, thin set, or any cement-based adhesive used to attach the tile, stone, marble or granite surround is acceptable. Only fire-rated caulking or adhesives may be used.

1 comment

Francina Marie Parks
Posted on Nov 14, 2011