Founding depth
Founding depth is the depth a footing must reach to bear on soil of adequate capacity, set by the geotechnical investigation and used in the AS 2870 footing design.
Ask Chalkline about this →Founding depth is the depth at which a footing must sit to bear on soil (or rock) of adequate load-bearing capacity. Near-surface ground is often too soft, too reactive, or filled to carry the load, so the footing has to reach down to a stratum that can. The founding depth is established by the geotechnical investigation, not guessed on site, and it feeds straight into the footing design under AS 2870.
The geotech drills or digs to log the soil profile (recorded in the borelog) and identifies the depth at which the bearing capacity is sufficient for the structure. On a deep-fill or highly reactive site, the founding depth can be well below the surface, which is why a Class P or Class H site can need piers or a deepened footing that reaches competent material. Founding on fill or reactive clay above the design depth is a direct path to footing movement, cracking, and a structural claim.
Read the founding depth and bearing recommendation in the soil report before pricing the footings. A founding depth deeper than the standard footing assumes can add piering and excavation cost that the base quote never carried, and it is far cheaper to find that in the report than in the ground. See reading a soil report and the site classification that drives the footing design.
Also known as: Founding level, bearing depth, footing founding level.
Category: Geotech / Footings.
Related
See also
References
- AS 2870:2011 Residential slabs and footings, Standards Australia (verified 2026-05-10)
- AS 1726:2017 Geotechnical site investigations, Standards Australia (verified 2026-05-10)
Last updated: 2026-05-30. Verified: 2026-05-10. Quarterly review for currency.