What Is a Deepened Footing?

Frost

• Deepened footings are often used where cold winters cause significant problems with ground heaving. Depending on what part of the country you're in, the frost line may be just below the soil surface or extend significantly below ground. In Michigan, for example, a deepened footing is necessary for just about any structure and must extend from 54 to 60 inches below ground so it falls below the frost line. In more southerly areas, the frost line is much closer to the surface. Placing a deepened footing several inches below the frost line then extending it upward to at least 3 inches above ground ensures the structure will not be subject to frost heaving and that the post outside of the footing does not contact soil.

Clay

• Clay is known as an expansive soil. It responds to water much like a sponge and transforms from a hard-packed, dense, dry state to a loose, spongy, wet material very quickly. In areas with clay soils, drought brings on multiple cracks in the soil surface as the dry clay contracts. Expansive soils require deepened footings to reach a better soil beneath the clay, such as bedrock. Bedrock gives the footings a solid foundation on which to rest and keeps them from being affected by fluctuations in moisture.

Poor Soil

• Poor soil is classed as a material that remains wet or contains too much organic matter. Organic material is in a constant state of change and, as it breaks down, causes an unstable surface on which to build. These soils not only require deepened footings to access firmer ground as in the case of clay but also require that the footing depth be equal to the distance between the edge of the wall to the outer edge of that footing. The added width increases the footing's load-bearing ability, as well as its stability.

Wide Vs. Deepened

• In some cases, poor soils may not require a deepened footing but only a widened one. These are usually reinforced with horizontal re-bar laid in the bottom of the footing prior to pouring. A wider, more shallow footing that is not reinforced is far more likely to crack under the weight of the structure and cause the building to settle unevenly into the ground.