Roots do not respect boundaries
A mature tree's root system commonly extends well beyond the drip line of its canopy, and most of it sits in the top half metre of soil where the oxygen and water are. That is also exactly where paths, driveways, slabs, footings and stormwater lines live.
In the Illawarra there is a local aggravating factor: the heavy clay soils on the western flats around Dapto and Horsley shrink and swell with moisture. A large tree draws water out of that clay in a dry spell, the soil contracts, and a footing over it moves. When the rain returns the clay swells again. Roots are part of that story but so is the soil, and that distinction matters a great deal when somebody is trying to prove a case.
Damage on your own land, from your own tree
Your tree, your problem. No one else is liable, and your insurer almost certainly excludes it.
The options are: remove the tree, install a root barrier between the tree and the structure, redesign the affected surface — a flexible path instead of a rigid one — or selectively prune roots under an arborist's direction. The root removal guide covers the technical side and surface roots covers the visible ones.
Damage from a neighbour's tree
Two routes exist and they overlap.
The common law. Encroaching roots causing damage can amount to a nuisance, and you also have the right of abatement — cutting roots at the boundary at your own cost, subject to the stability warning above and to council tree controls. Negligence is available where the owner knew or should have known of a risk and did nothing.
The Trees (Disputes Between Neighbours) Act 2006 (NSW). The Land and Environment Court can make orders about a tree on adjoining land that has caused, is causing or is likely in the near future to cause damage to property, including orders for compensation, pruning, removal and works. The dispute process guide sets out the steps.
Note again that this is the 2006 NSW Act, not the Queensland legislation of 2011 that appears in a great deal of online material.
Damage from a council tree
Council street trees are a separate process, handled through council rather than the Act. Whether council is liable generally turns on whether it knew or should have known about the problem, which is why reporting it in writing and keeping the reference number matters so much. See council trees overhanging property.
What evidence you actually need
Photographs, dated, showing the damage and its relationship to the tree. Quotes for the repair. Where the amount is significant, a report — an arborist to identify the roots and confirm the species and their likely extent, and often an engineer or a builder to establish the mechanism of the damage.
The common failure is assuming causation is obvious. A cracked slab near a tree is not proof the tree cracked it. Reactive clay, poor original construction, a leaking stormwater line and vehicle loading all produce similar cracking, and a defendant will say so.
Prevention is cheaper
Do not plant large-rooted species close to structures. Figs, liquidambars, poplars, willows and camphor laurels are the repeat offenders in this region, and the mature Port Jackson and Moreton Bay figs through central Wollongong are in a class of their own.
Where a tree is already in the wrong place and the structure matters more, removal and stump grinding is the cheaper end of the problem. Ring (02) 4210 5885 for an assessment. This is general information, not legal advice.
Frequently asked questions
My neighbour's tree roots cracked my driveway. Who pays?
It depends on evidence rather than principle. Under the Trees (Disputes Between Neighbours) Act 2006 the Land and Environment Court can order compensation for damage caused by a tree on adjoining land, and can order work on the tree. You have to show the tree caused the damage, which usually needs an arborist or an engineer rather than an assertion, and you have to have raised it with the neighbour first.
Does home insurance cover tree root damage?
Usually not. Most Australian home building policies specifically exclude damage caused by tree roots, on the basis that it is gradual rather than sudden. Storm damage from a falling tree is a different matter and is generally covered. Read your product disclosure statement rather than assuming, because the wording varies and the exclusions are where the money is.
Can I just cut the roots on my side?
You have the right to cut roots that encroach onto your property, but doing it can destabilise the tree, and if the tree then falls on something the question of who caused that becomes very live. Structural roots near the trunk are what hold the tree up. Anything substantial should be assessed by an arborist before it is cut, and preferably in writing.