What is the proper depth for footing below frost line to prevent shifting?

The proper depth for footings below the frost line is crucial to prevent shifting due to freeze-thaw cycles. The frost line, which can vary based on geographical location, refers to the depth at which the ground is expected to freeze in winter. In many areas of Virginia, a depth of 18 inches is commonly recommended for footings to ensure stability, as this depth is generally below the frost line and minimizes the risk of frost heave that can occur when water in the soil freezes and expands.

Choosing 18 inches helps ensure the footing remains stable against the pressures exerted by a frozen and thawing ground. If the footing is not placed deep enough, the structure may shift or settle unevenly as the ground expands and contracts with temperature changes, potentially leading to structural damage. Therefore, the recommendation of 18 inches stands as a standard practice to ensure the longevity and stability of residential foundations in Northern Virginia and many other regions subject to freezing temperatures.