Kalantzis v Brown; Brown v Kalantzis [2026] NSWCA 17

What happened

• Neighbours in Gosford disputed damage after excavation for an apartment development on the adjoining lot.

• Excavation works encroached across the boundary (including into the subsoil), geotechnical warnings were ignored, and the neighbour’s driveway later collapsed into the site.

• The trial judge found the developer, builder, and several individuals (including family members involved in site works) liable in trespass and negligence, and awarded rectification damages.

What the Court of Appeal decided

• Appeals by two individual defendants (Alex and Nick Kalantzis) were dismissed.

• Cross‑appeals by the neighbour (Mr Brown) were allowed in part so that trespass was treated as intentional and not subject to proportionate liability apportionment.

• Personal liability of individuals was upheld where they personally undertook excavation, encroached over the boundary, or failed to implement obvious geotechnical precautions.

• Causation was inferred from the timing and nature of the works: removing support near the boundary materially contributed to the collapse.

• Rectification cost was the appropriate measure of damages for a home, despite being higher than diminution in value.

Why it matters

• Excavating over or under a neighbour’s land is trespass. Intention is satisfied by deliberately doing the excavation, even if the boundary is misunderstood.

• The statutory duty of support (Conveyancing Act 1919 (NSW) s 177(2)) applies to excavation next to residential land; ignoring geotechnical advice is likely to be a breach.

• Proportionate liability defences must be precisely pleaded. Courts will not allow late attempts to spread liability to others not identified as concurrent wrongdoers.

• For residential property, courts commonly award rectification costs where reinstatement is reasonable.

Key takeaways

• Boundary encroachment into subsoil = trespass; mistaken belief about the boundary is no defence.

• Intentional trespass is not apportionable under Pt 4 of the Civil Liability Act 2002 (NSW).

• Individuals involved in, directing, or personally performing negligent site works can be personally liable.

• Compliance with geotechnical recommendations and development conditions is critical to manage collapse risk.

• Rectification damages will often be preferred for homes, even if exceeding diminution in value.