What is the minimum depth of footings for shallow foundations below the undisturbed ground surface?

The minimum depth of footings for shallow foundations is critical for ensuring stability and proper load distribution. A depth of 12 inches below the undisturbed ground surface is commonly accepted as the minimum standard for shallow foundations. This depth allows for adequate support against lateral and vertical loads, helps avoid issues such as frost heave in colder climates, and ensures that the footings are below the influence of surface moisture and soil disturbance.

Choosing a depth of 12 inches strikes a balance between structural integrity and practicality, as it typically allows for the design to accommodate various soil conditions and building loads. The other depths provided, while they may be adequate in certain conditions, do not represent the minimum standard typically used across various building codes, making 12 inches the correct choice for the baseline requirement in most scenarios.