What bearing capacity means for a home
Bearing capacity relates to how the ground can support loads transferred through a footing or foundation. For a residential project, the structural designer needs ground information appropriate to the proposed structure, founding depth, footing geometry and conditions encountered.
A soil class describing moisture-related movement is not the same as a full bearing assessment. Depending on the proposal, both ground movement and founding conditions may be relevant, but they answer different engineering questions.
Factors that can affect founding conditions
Fill, soft soil, variable weathered material, rock, groundwater, previous excavation and proposed building loads can change the suitability of a founding layer. Conditions may vary across the footprint, particularly on sloping or previously developed sites.
The appropriate geotechnical investigation should relate field observations, selected testing and engineering interpretation to the proposed footing design. Generic values taken from a suburb or internet table should not be substituted for site-specific advice.
- Proposed building loads and footing configuration.
- Depth, thickness and variability of founding materials.
- Presence and condition of placed fill or disturbed ground.
- Groundwater, drainage and excavation conditions.
- Nearby slopes, retaining walls and changes to levels.
- Whether construction-stage inspection or verification is needed.
How geotechnical and structural roles work together
The geotechnical engineer investigates and interprets the ground within the agreed scope, while the structural engineer designs the footings or structural foundation system. Recommendations should be read with the report's assumptions, limitations and any requirement to confirm conditions during excavation.
If the actual exposed ground differs from the report assumptions, the project team may need an inspection or revised advice before proceeding.
Provide architectural and structural drawings, proposed footing loads or details if available, the site survey, existing report and any identified fill, slope, excavation or groundwater concerns. Explain whether a footing excavation is already open or an inspection is required before concrete placement.
Sydney Geotechnical can assess whether the project needs an AS 2870 classification, broader foundation investigation or a targeted construction-stage inspection.
Common questions
Residential foundation bearing capacity: common questions
Is a site classification the same as bearing capacity?+
No. An AS 2870 site classification primarily supports residential footing design by considering site reactivity and relevant conditions, while bearing assessment addresses the support provided by particular founding materials.
Who designs the residential footings?+
The structural or appropriately responsible footing designer completes the structural design using the relevant project details and geotechnical information.
Why might an excavation need inspection?+
A geotechnical inspection can help confirm that the exposed founding conditions are consistent with the assumptions and recommendations relevant to the agreed scope.
Need geotechnical foundation investigation in Sydney?
Get a scope matched to the project
Send the site address, proposed works, current plans and any request from your builder, engineer, council or certifier. Sydney Geotechnical will review the information and confirm an appropriate scope and fee.
This guide provides general information only and is not a substitute for investigation, engineering advice, footing design or approval advice for a particular property. Project requirements and ground conditions must be assessed site by site.
