A residential footing or slab must be designed for the conditions beneath the proposed building. For relevant housing projects, site classification under AS 2870 helps the structural or footing designer consider expected movement, reactive soil and significant site features.
Homeowners often call this process a 'soil test'. The actual requirement and scope depend on the proposed dwelling, existing information, site conditions and the needs of the designer, builder, certifier or approval authority.
New homes, replacement homes and vacant lots
A new home on a vacant block usually requires reliable site information for the proposed footing design. However, a report prepared before demolition, earthworks, filling or a changed building layout may no longer address the current proposal adequately.
For knockdown-rebuild projects, existing slabs, previous excavations, landscaping, buried services and access restrictions may affect both the investigation and interpretation. Tell the consultant whether the existing dwelling remains in place when fieldwork is proposed.
What site classification can identify
A site assessment considers relevant soil and moisture conditions, possible reactive clay, fill, slope and other features that may affect residential footings. The resulting classification is project-specific; Class P, where applicable, indicates conditions needing further consideration rather than automatically meaning the land cannot be developed.
An AS 2870 site classification does not replace structural design. If the site also involves a basement, retaining wall, substantial slope or unusual founding conditions, broader geotechnical input may be needed.
What to send when requesting a quote
Provide the property address, proposed dwelling plans, survey, builder or designer request, any prior report and photographs showing access. Include details of demolition, previous fill, significant trees, recent earthworks and any council or certifier wording.
Sydney Geotechnical's site classification service starts from $750 for a suitable residential scope. The final quote depends on the site and requested engineering deliverables.
Common questions
Soil tests before building in NSW: common questions
Does every NSW house need exactly the same soil test?+
No. Appropriate ground information depends on the proposed dwelling, footing design, site conditions, available previous information and requirements of the project professionals or approval authority.
Can I rely on a developer's estate-wide soil information?+
Estate information may provide useful background, but the footing designer may still need a site-specific assessment addressing the individual lot and proposed building footprint.
What does a Class P result mean?+
Class P indicates a site with conditions requiring project-specific engineering consideration, such as fill, unusual moisture, soft ground or slope. It does not automatically prohibit construction.
Need AS 2870 site classification 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.
