Exterior Wall Thickness
Unlike many interior walls, exterior walls need to be thick enough to provide adequate insulation. This yields 2 extra inches for insulation but increases the cost of other areas, such as windows and doors installation. Each strap shall be fastened to not less than four floor ceiling or floor joists or rafters with two 1/2-inch (12.7 mm) bolts. The fireplace throat or damper shall be located not less than 8 inches (203 mm) above the lintel. Where the inside surface of the smoke chamber is formed by corbeled masonry, the walls shall not be corbeled more than 30 degrees (0.52 rad) from vertical. The minimum thickness of fireplace hearths shall be 4 inches (102 mm).
Codes are organized by jurisdiction to help you understand which regulations apply to your project.