What does a Class P site classification mean?
Class P identifies a problem site where standard assumptions for residential footing design may not adequately address the relevant site conditions. The classification does not automatically mean a property cannot be developed, and it does not prescribe one universal foundation solution.
Conditions potentially relevant to a Class P assessment include uncontrolled fill, unusual moisture conditions, trees, erosion, unstable slopes, mine subsidence, soft ground or other site-specific factors. The actual cause must be established through a professional assessment of the individual property.
Foundation options must follow the actual ground risk
A structural engineer may consider project-specific footing, slab, pier or founding solutions based on the identified ground conditions and the recommendations in the geotechnical report. The appropriate design depends on the development, loading, depth of suitable material and the nature of the identified problem.
Where fill, slope, groundwater, trees or variable bearing conditions are involved, additional investigation may be appropriate before the designer finalises the foundation system. An article cannot determine the correct design for a particular Class P property.
What to provide when requesting advice
Send the existing soil or site-classification report, architectural and structural plans, site address and any council, certifier or builder correspondence. Tell the engineer about known fill, retaining walls, nearby trees, drainage issues and previous movement or cracking.
Greater Sydney and Western Sydney sites can have highly variable conditions between neighbouring properties. Decisions should be based on the actual site and proposed development rather than a suburb-wide assumption.
Common questions
Class P foundations and assessment: common questions
Can you build a house on a Class P site?+
A Class P classification does not automatically prevent construction. Whether and how a project can proceed depends on the identified site issues, engineering assessment, design and applicable approval requirements.
Does Class P always mean highly reactive clay?+
No. Class P can relate to a range of problem-site conditions, including fill, unusual moisture conditions, slope instability or other site-specific factors.
Who designs the foundations for a Class P site?+
The foundation system is designed by the appropriate structural designer using relevant project-specific geotechnical information and other applicable design requirements.
Need Discuss your Class P site 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.
