Hearth & Wall Extensions

Floor Protection

If hearth extensions are to be placed over combustible floors, it is necessary to ensure that combustible materials under the hearth extension are properly protected. The fireplace installation manual will normally give specifications for the thickness and insulation value of acceptable noncombustible hearth extensions materials. Many manufacturers supply factory-produced hearth extensions of appropriate size and thickness to meet the minimum criteria for floor protection. These factory hearth extensions may be covered with decorative tile, stone, brick or other desired noncombustible materials.

If factory hearth extensions are not used, it is important to make sure that the substituted materials are also noncombustible and are of equivalent or superior insulating values. The manufacturer's instructions state that alternative hearth extension materials must have certain minimum thickness and certain minimum thermal properties. Examples of how to calculate the required thickness of alternate materials are provided in the manufacturer's installation instructions.

Manufacturers do not always use the same parameters when providing information on the thermal properties of alternate materials. Thermal properties can be expressed as:

1. k, thermal conductivity per inch;
2. C, total thermal conductivity;
3. R, total thermal resistance of a single material;
4. U, total thermal resistance of a composite cross-section.

Make sure that all materials are durable in construction and anchored securely so they cannot become dislodged or moved.

NOTE: All factory-built fireplaces do not have the same material and thickness requirements; therefore, always follow the manufacturer's instructions as the requirements for the particular factory-built fireplace model being installed.