What is the prescribed elevation of footings under different frost conditions?

The requirement for footing elevations in areas with varying frost conditions is crucial for ensuring structural integrity and preventing frost heave. When ground freezes, it expands, which can exert significant pressure on foundations and footings.

In regions where frost is a concern, the typical code stipulation is to place footings below the frost line to avoid the potential for damage due to ground movement. The option indicating 18 inches below grade is commonly based on many building codes, which advocate for footings to be placed deep enough to prevent frost from impacting the foundation.

The selection of 18 inches as the prescribed elevation is well-supported by building practices, as this depth is often sufficient to reach stable soil conditions unaffected by freezing temperatures, depending on local climate conditions. Therefore, establishing footings at this depth helps mitigate any risk associated with frost heave, maintaining the stability and durability of the structure.