Trees, Roots and Reasonable Cost: What Delaware Mansions Still Means for Subsidence Claims
posted 28th July 2026
A leading House of Lords authority on tree root damage
Subsidence caused by tree roots remains one of the most common and contentious issues we deal with across the HA5 area and further afield, particularly on clay subsoils. When a claim involves a tree on neighbouring or highway land, the question of liability, and just as importantly the measure of damages, often comes down to one case: Delaware Mansions Ltd v Westminster City Council [2001] UKHL 55; [2002] 1 AC 321.
Decided by the House of Lords on 25 October 2001, this remains the leading authority on liability for tree root subsidence and on how the cost of remedial works is assessed once that liability is established.
The facts
Delaware Mansions, a block of flats in Westminster, suffered structural cracking caused by a large plane tree growing on the adjoining highway. The tree was owned and maintained by Westminster City Council. Its roots drew moisture from the clay subsoil beneath the building, causing progressive subsidence.
The freeholder had the building underpinned to arrest the ongoing movement, at a cost of around £570,000, and sought to recover that sum from the council.
A complicating factor was timing. The cracking had first appeared before the claimant acquired its interest in the building. The council argued that any cause of action had accrued to a previous owner, not to the claimant who had actually commissioned and paid for the underpinning.
Did the tree owner have to pay towards the underpinning?
Yes. This is worth stating plainly, since it is the point most practitioners take away from the case. Westminster City Council, as owner of the tree, was held liable in nuisance and was required to meet the cost of the underpinning works. The House of Lords confirmed that a landowner who has knowledge of a hazard emanating from their land, in this case a tree causing ongoing subsidence, and who fails to take reasonable steps to abate it, will be liable for the reasonable cost of remedial works needed to remove the continuing threat.
The legal issues
● Whether the council, as owner of the tree, was liable in nuisance for damage caused by its roots.
● Whether the cost of remedial underpinning was the correct measure of loss, as opposed to the cost of repairing visible cracking as it stood at some earlier date.
● Whether a claim could succeed where the claimant acquired the property after the damage had first appeared, given that the underpinning works were carried out during their ownership.
The decision
The House of Lords, in the leading speech of Lord Cooke of Thorndon, found in favour of the claimant on all counts.
The council was liable in nuisance, applying and extending the principles established in Leakey v National Trust [1980] QB 485: where a landowner has knowledge of a hazard, whether natural or otherwise, emanating from their land, and fails to take reasonable steps to abate it, liability follows.
The correct measure of damages in a continuing nuisance of this kind is the reasonable cost of the remedial works required to remove the threat of further damage, not simply the cost of repairing the damage as it stood at an earlier point in time.
Most significantly for practice, the House of Lords held that what matters is whether the nuisance, that is, the continuing risk from the roots, was still causing danger at the time the remedial works were carried out. Ownership history is not the decisive factor. Because the threat was continuing and the underpinning was reasonably necessary to abate it, the claimant, as owner at the time the works were carried out, was entitled to recover the full cost, even though the damage had first appeared under a predecessor's ownership.
Why this still matters
Delaware Mansions is the key authority for two propositions that come up repeatedly in subsidence work:
● Damages in tree root and continuing nuisance cases are assessed by reference to the cost of abating the ongoing hazard, rather than being tied strictly to a fixed historic loss.
● A claim is not defeated simply because there has been a change of ownership since the damage first became apparent, provided the nuisance is continuing and the remedial works are reasonably necessary.
For building owners, managing agents and local authorities alike, this case underlines the importance of acting promptly once root-induced movement is identified. Failing to abate a known hazard from a tree, whether on your own land or land you control, can leave you liable for the full cost of remediation, regardless of when the cracking first appeared or who owned the affected building at the time.
If you are dealing with suspected tree root subsidence, or a dispute over liability for root damage from a neighbouring or highway tree, our team at Tayross Associates can advise on causation, liability and the appropriate scope of remedial works.
