Underpinning & Footing Repair
Underpinning and footing repair for subsidence and inadequate footings — mass-concrete or screw-pile underpinning and footing reconstruction to re-establish load transfer to stable ground.

When a footing can no longer carry its load to stable ground, everything above it starts to move. Cracking walls, dropping floor levels, and doors that no longer close are the visible symptoms; the cause is a foundation that has lost bearing — through subsidence, soil movement, erosion, or footings that were undersized or shallow to begin with. Underpinning re-establishes that lost load path by extending support down to competent soil or rock, so the structure is carried properly again.

There is more than one way to underpin, and the right method depends on the depth to stable ground, the soil, and the access available. Traditional mass-concrete underpinning — excavating in short, sequenced bays beneath the existing footing and pouring new concrete — suits shallower cases. Where competent ground is deep, access is tight, or the loads are high, screw piles (helical piles) driven to a verified capacity transfer load past the unstable zone. In some cases the footing itself is beyond repair and is reconstructed.

Atomic Projects delivers underpinning and footing repair under structural-engineering design, to AS 2159 (Piling — Design and Installation) and AS 3600 (Concrete Structures). Because underpinning is only as good as the diagnosis behind it, we address the cause — including the drainage and soil-moisture factors that drive movement in Sydney's reactive clays — so the repair holds rather than simply moving the problem along.

How We Deliver Underpinning & Footing Repair

  1. Engineering & Geotechnical Assessment
    • Structural engineer confirms the cause and extent of footing movement; geotechnical input establishes bearing conditions and depth to stable ground.
    • Level surveys and crack monitoring confirm whether movement is active before committing to a method.
  2. Method Selection
    • Mass-Concrete Underpinning: Sequenced bay excavation and concrete pours beneath the existing footing for shallower stable ground.
    • Screw-Pile / Helical Underpinning: Piles installed to a verified capacity to transfer load to deeper competent strata, suited to poor soils and restricted access.
    • Footing Reconstruction: Replacing or enlarging footings where the original is inadequate.
  3. Sequenced Excavation & Support
    • Work in short bays so the structure is never undermined — no more than a controlled proportion of a footing is unsupported at any time.
    • Support the structure as required throughout.
  4. Load Transfer & Reinstatement
    • Establish the new load path to stable ground and pack/dry-pack to the underside of the existing footing to engage it.
    • Reconstruct footings where specified.
  5. Drainage & Make-Good
    • Address subsoil drainage and surface grading to control the moisture that drives clay movement.
    • Reinstate surfaces and provide engineer verification and as-built records.

When Underpinning Is Required

  • Differential Settlement – One part of the building dropping relative to another, cracking the structure.
  • Reactive-Soil Movement – Seasonal shrink-swell in clay soils undermining bearing.
  • Erosion & Scour – Wash-out of supporting soil after storm, flood, or drainage failure.
  • Inadequate Original Footings – Shallow or undersized footings unable to carry current loads.

Why Atomic Projects for Underpinning

  • Cause-First, Not Symptom-First: We confirm the driver of movement and address drainage and soil moisture, so the repair is durable.
  • Engineer- & Geotech-Designed: Method and capacity designed to AS 2159 and AS 3600, with verified load transfer.
  • Occupied-Building Sequencing: Bay-by-bay works keep the structure stable and the building in use throughout.

Frequently Asked Questions

How do we know if our building actually needs underpinning?

Underpinning is warranted when a structural engineer confirms that footing movement is active and caused by loss of bearing — not every crack means the foundation is failing. The usual indicators are differential settlement (one area dropping relative to another), diagonal cracking wider at the top, and floor level changes, confirmed by level surveys and crack monitoring over time. The decision follows an engineering and, where needed, geotechnical assessment — never appearance alone.

What's the difference between mass-concrete underpinning and screw piles?

Mass-concrete underpinning extends the existing footing downward by excavating in short bays and pouring concrete beneath it — it suits cases where stable ground is relatively shallow. Screw piles (helical piles) are driven to a verified capacity to carry load to deeper competent strata, and are preferred where good ground is deep, soils are poor, or access is too restricted for large excavations. The engineer selects the method from the geotechnical conditions and the loads; both are designed to AS 2159.

Can underpinning be carried out while the building stays occupied?

In most cases, yes. Underpinning is carried out in short, sequenced bays so only a controlled proportion of any footing is unsupported at once, keeping the structure stable throughout. Screw-pile systems in particular can often be installed from limited access with less excavation. Residents typically remain in place, with localised access restrictions and some noise and vibration during excavation or pile installation. We stage works with the strata or building manager to minimise disruption.

Does underpinning require an engineer's report and certification?

Always. Underpinning alters the structural foundation and must be designed by a structural engineer, with geotechnical input on bearing conditions. In NSW this work also requires certification, with inspection by the Principal Certifier at key stages, and is delivered to AS 2159 (Piling) and AS 3600 (Concrete). We co-ordinate the engineering, geotechnical, and certification requirements within our scope and provide the as-built documentation the owners corporation needs.

Will underpinning stop the movement permanently?

Underpinning re-establishes support to stable ground, and when the cause is correctly diagnosed and the drainage and soil-moisture drivers are addressed, it is a permanent stabilisation. The critical factor is dealing with what caused the loss of bearing in the first place — underpinning without correcting, for example, a drainage failure that is scouring soil can leave the structure exposed to renewed movement. That is why we treat cause diagnosis and drainage management as part of the works, not an afterthought.

Related Services

Underpinning isn't just digging under a wall — it's re-establishing a lost load path to stable ground, and it only holds if the cause of the movement is dealt with too. As a Class 2 Registered Builder with over 10 years of experience in structural remediation across Sydney, Atomic Projects delivers underpinning and footing repair that is engineered, verified, and built to last. Call us on 0410 515 509 or email hello@atomicprojects.com.au to arrange an assessment.

— Ben Tran, General Manager, Atomic Projects