Retaining Wall Footing Depth: The Right Number

Footing depth affects two things: frost heave and bearing capacity. Get it wrong and the wall lifts in winter or slowly sinks.

Frost depth rule

Most building codes require the bottom of the footing to sit at or below the local frost depth — the point below which the ground doesn't freeze. In northern states this can be 48 inches or more; in the south it's effectively zero.

Use the calculator to find the frost depth for your state; it pulls from ASCE 7 ground temperature data. For a quick check: Minnesota is ~60 in, Chicago ~36 in, North Carolina ~12 in, Texas ~4–6 in, Florida ~0.

Bearing capacity rule

Even in a frost-free zone, the footing should sit on undisturbed, competent soil. If the existing grade is fill, topsoil or disturbed material, go down until you hit native ground regardless of the frost rule. Minimum bearing for most residential walls is 1,500 psf.

Segmental block vs poured walls

Segmental block walls (SRW) don't have a traditional poured footing — instead they use a compacted crushed-stone leveling pad, typically 6 inches deep, with the first block course buried. The pad distributes the load; the buried course prevents undermining.

Poured concrete walls (gravity or cantilever) need a real cast-in-place footing: typically 1 ft wide for every 1 ft of wall height, at frost depth. An engineer specifies this based on bearing tests for anything over 4 ft.

Bottom line

For SRW block: 6-inch stone pad, first course buried, total excavation depth = pad + one block (≈ 16–18 inches). For poured concrete: match frost depth, minimum 12 inches below grade for warm climates. The calculator shows which rule applies to your configuration.