A footing is the bottom-most portion of a building's foundation. It makes contact with the soil below and distributes the building's weight evenly. The depth that a footing needs to be in the ground depends on several factors, including the weight of the building, the load-bearing capacity of the soil and the frost line, which is the average depth at which the soil freezes. According to HomeTips.com most concrete footings are located approximately 1 foot below the soil's frost line.
Integral concrete footings are integrated into their foundations, which means there is no physical separation between the two components. As ConcreteNetwork.com notes, creating integral footings requires pouring additional concrete along the edges of a foundation so these edges become thicker and increase the structure's ability to distribute its weight evenly. Workers install steel reinforcing rods in these thick edges to strengthen them. The type of foundation structures that integral footings support are known as monolithic slab or slab-on-grade, which means the footings, foundation and slab -- or uppermost building surface -- are all poured together. Buildings in areas with warm climates most commonly utilize integral concrete footings, as the footings do not need to penetrate far to extend below the frost line.
Continuous Spread Footing
Similar to integral footing, continuous spread footing underlies the edges or perimeter of the building it is supporting and typically consists of steel-reinforced concrete. However, instead of being directly connected to the layers of concrete above, these footings consist of separate, continuous blocks. As separate components, continuous spread footings can go deeper than their integral counterparts and are suitable for areas with colder climates and lower local frost lines. According to Raised Floor Living, most spread footings have thicknesses of between 6 and 16 inches and widths between 16 and 24 inches. Concrete foundations that utilize continuous spread footings are known as raised-perimeter foundations.
As Raised Floor Living notes, buildings that utilize continuous spread footings may also incorporate spot footings into their foundation designs. Alternatively, some buildings utilize spot footings exclusively. The footings provide support to specific structural components that rest atop the foundation and slab, such as beams or posts. Spot footings consist of large pads or flat blocks of reinforced concrete that are typically 2-by-2 feet and between 10 and 12 inches thick, as Raised Floor Living notes. Foundation structures that utilize spot footings are known as post and pier foundations or T- shaped foundations. The latter name stems from the fact that when concrete foundation columns come to rest on the much wider footings below, the components form an upside-down T-shape. Due to the depths at which these "upside-down T's" can penetrate, spot footings are good for areas with low frost lines.