In masonry construction, why is it critical for footings to extend below the frost line?

In masonry construction, it is essential for footings to extend below the frost line primarily to prevent heaving and settling in cold weather. When the ground freezes, soil expands, and if footings are not deep enough, this freeze-thaw cycle can cause them to shift or lift. This phenomenon can lead to structural damage, such as cracks in walls, uneven floors, or even complete failure of the foundation. By ensuring that footings are placed below the frost line, builders create a stable base that is less susceptible to the effects of freezing and thawing, thereby maintaining the integrity of the structure throughout the changing seasons.

The other choices, while related to construction and building practices, do not directly address the critical need to extend footings below the frost line for structural stability in cold weather conditions.