Footings for masonry fireplaces must extend below what specific level?

For masonry fireplaces, footings must extend below the frost line to ensure structural stability and prevent heaving due to freeze-thaw cycles. The frost line, or frost depth, is the depth at which the ground is expected to freeze during winter months. When footings are placed above or at the frost line, they are susceptible to movement from ground freezing, which can lead to cracks or other structural issues in the fireplace and surrounding areas. By extending the footings below the frost line, the masonry work remains stable, reducing the risk of structural problems caused by ground movement in colder climates. This practice is crucial in areas with significant frost depth, as it maintains the integrity of the fireplace over time.