What is the required thickness of solid masonry between flue liners and combustible material?

The required thickness of solid masonry between flue liners and combustible material is established to ensure the safety and fire resistance of the construction. A thickness of 8 inches provides a sufficient barrier to prevent heat transfer to combustible materials, which could lead to a fire hazard. This specification is crucial in maintaining safe distances and thermal resistance, allowing for proper ventilation and minimizing the risk of fire within masonry structures. The recommended thickness is grounded in building codes and fire safety regulations, which are designed to protect both the integrity of the structure and the safety of its occupants.