Tree-related subsidence is quite a common occurrence on shrinkable soils (e.g. clay) and I have addressed this some time ago already (to a limited specificity). In cases where the tree(s) in question is a low-value tree and / or there is no degree of statutory protection afforded to the tree, the landowner may very well consider it appropriate to remove the tree or otherwise prune the tree to address water uptake (see the Hortlink study and additional Building Research Establishment publications, for more information). In a situation where the tree(s) implicated in cases of subsidence where the evidential tests have been satisfied ([1)] has actual damage occurred that is consistent with subsidence damage?;  have roots encroached under the foundations that are damaged?, and;  was the damage from adjacent tree[s] foreseeable?) and the tree(s) is subject to a Tree Preservation Order, it may very well be necessary to consider the management of the situation in a more holistic lens. Specifically, this is because of the precedent set by the case Perrin & Anor v Northampton Borough Council & Ors  EWCA Civ 1353 (19 December 2007).
As a precursor before continuing, it is important to recognise that the case being discussed below must never be considered in isolation – therein, nor should the decision be made in blunt isolation. Subsidence damage as caused by a tree subject to a Tree Preservation Order is an issue that demands cross-profession liaison; specifically, between at least the arboriculturist, planning officer / manager, and insurance officer / manager for the Local Planning Authority (i.e. Local Council), in addition to the tree owner and their insurer – plus the homeowner with a damaged house and their home insurer – where the tree is a third-party tree). The economics and logistics of any given situation are key and the role of the arboriculturist is not to operate as a lone professional but to engage and be willing to compromise where there is an evident requirement for this.
Returning to the case, the situation involved a privately-owned oak tree subject to a TPO that had been determined to be causing subsidence damage to an adjacent property. The claimants applied for permission from the Local Planning Authority (LPA) to remove the oak tree, which was refused on the grounds that it was “not necessary to fell the tree, not because felling would not abate the nuisance (it obviously would), but because other engineering works, such as the underpinning of the claimants’ house, could be carried out instead, thereby curing the problem and preserving the tree” – in more detail, the LPA stated that “the tree proposed for removal is a tall, broad-spreading and healthy specimen [that] stands in the garden of a house overlooking the open valley that defines the western edge of the old core of the village of Great Billing [and] forms a handsome and prominent feature in views along and over the valley, part of which is a public park, and is also an amenity to the village and its conservation area (within which the [tree stands]), particularly in views from the direction of the Parish Church of St Andrew [so] consequently the removal of the tree would have a significantly detrimental impact on the amenity of a wide area and its enjoyment by the public“. The claimants subsequently appealed to the Secretary of State and the appeal was dismissed. This resulted in the court case and the resultant appeal that is the subject of this discussion. The claimants argued that the then current TPO protection did not apply to the oak tree, because Section 198(6)(b) of the Town and Country Planning Act 1990 did not apply (as abating the nuisance of subsidence was a legal exemption to the TPO).
The summarised original ruling – known as Perrin & Anor v Northampton Borough Council & Ors  EWHC 2331 (TCC) (26 September 2006) – by the Technology and Construction Court (TCC) was that “the possibility that other engineering works could be carried out is irrelevant” (with the caveat that only “in the vast majority of cases, the fact that alternative engineering schemes are available would indeed be irrelevant“), because “the TPO will not apply to whatever cutting down, uprooting, topping or lopping of the tree is necessary to abate or prevent that nuisance” that was in this case subsidence damage caused by the oak tree. The judge determined that this conclusion was a “workable solution to the problem posed [and] also fair” (because it “would be unworkable if a member of the public had to weigh up all the factors listed [in paragraph  of his judgment] before coming to a clear view as to whether or not works to the tree were necessary“). Thus, the judge agreed with the claimants as regards the scope of Section 198(6)(b) that it was necessary to remove the oak tree to abate the nuisance and prevent further damage. Northampton Borough Council disagreed and took this to the Court of Appeal.
The judges at the Court of Appeal went to some length to pull apart the meaning of Section 198(6)(b) and the TCC judge’s interpretation – particularly, whether the removal of the oak tree was necessary, in context to this Section (“this appeal turns on whether the judge was correct in his conclusion that the word ‘necessary’, in the context of section 198(6)(b) of the 1990 Act“). Critically, the judges concluded that the TCC judge was incorrect in his conclusion, because the judge had failed to appreciate that it was indeed appropriate to consider engineering solutions in the extent as to what is necessary in abating and preventing further nuisance when applying the exemptions of Section 198(6)(b). Very importantly, the judges also determined that “it is pertinent to have in mind that nothing in section 198(6)(b) of the 1990 Act authorises B to go onto A’s land for the purpose of preventing or abating a nuisance“, which means that even if the claimants had opted to apply the exemption of the Section they would be trespassing if they did indeed proceed to fell the oak tree not within their land. Legally and logistically, the original judge’s conclusion is thus flawed, for this reason plus others noted in the judgement.
Moreover, the judges determined that “Parliament plainly intended that, in such a case and subject to obtaining the consent of, or compensation from, the local planning authority, A is left to bear his own loss: a risk which, in the ordinary way, he will cover by insurance. In those circumstances it is not self-evident why Parliament should have wished to encourage A to carry out operations to the tree in order to abate or prevent damage to B’s house, so relieving A from his liability in damages” – or, plainly-interpreted, a homeowner has insurance for matters including subsidence and therefore Section 198(6)(b) would not logically allow as an exemption the removal of a tree for the purposes of abating and preventing further subsidence damage. Indeed, “in that context it is to be borne in mind that the expectation that a refusal of consent [by the LPA and even afterwards by the tree owner] will give rise to a claim for compensation [by the homeowner with a damaged house] has been a feature of the legislation since tree preservation orders were first introduced” – or, in short, if the LPA refuse the application for the removal of the TPO’d tree then the affected party / parties can claim against the LPA for the costs incurred for employing an engineering solution such as underpinning (or the homeowner, if they then refuse to remove the tree in spite of consent by the LPA).
The judges rounded-up by asserting that, in their determination, it is “intended that a protected tree should remain protected unless there was a real need to lift that protection” and that that the phrase in Section 198(6)(b) of “so far as may be necessary for the prevention or abatement of a nuisance” be interpreted as “‘if and so far as may be necessary for the prevention or abatement of a nuisance’“. In fact, the judges “[found] it difficult to see how the expression can be read in any other way“, because “if it were appropriate to ask what is the minimum that needs to be done to the tree itself in order to prevent or abate the nuisance, should it be irrelevant to ask whether anything needs to be done to the tree itself[?]“. Bluntly, is it not irrelevant to consider engineering solutions (e.g. underpinning) in cases where the implicated tree is subject to a TPO, because one cannot proceed “without first asking whether anything needs to be done to the tree itself“. Clearly, in some cases, nothing needs to be done to the tree.
As a means of context-proofing their determination, the judges appended their main determination with the statement as follows: “if prevention or abatement of a nuisance could be achieved either by operations to the tree itself or by works other than operations to the tree itself and the landowner has the resources to fund the former but not the latter, it may well be that the operations to the tree itself are necessary because the other works cannot, and will not in practice, be done” – simply, if a landowner cannot afford to subsidise the underpinning works to the affected’s property, it may be most economical to remove the tree and this is indeed acceptable. However, the judges “suspect that will rarely be a determinative factor; given that the costs are likely to fall not on the landowner but on his insurer (subject to whatever claim to compensation there may be)“. In addition, “in practice, it will be for the [tree owner] rather than the [homeowner with a damaged property] to decide whether to cut down the protected tree; or to pay damages in respect of the costs of remedial or preventative works” – or by extension the LPA insofar as they refuse to consent the removal of the implicated TPO’d tree.
As a very straightforward summary, the appeal case of Perrin & Anor v Northampton Borough Council & Ors  EWCA Civ 1353 (19 December 2007) therein determined that where a tree subject to a TPO is implicated in a subsidence damage claim – and permission for removal is sought from the LPA – it cannot be assumed that removal will be consented. Indeed, the LPA can rightly refuse consent, citing the need for an engineering solution. In such an eventuality, the LPA will however be liable to subsidising the costs of the engineering solution – or, if the LPA grant consent for removal and the tree owner refuses, this responsibility passes on to the homeowner (or their own insurer). In this eventuality, it is pertinent for the LPA at least to consider the theoretical value of the tree(s) by assessing them in line with a valuation system such as Capital Asset Valuation of Amenity Trees (CAVAT), which can help equate the value of the trees against the cost of underpinning (including the associated activities to facilitate the underpinning).