Wright & Anor v Horsham District Council [2011] UKUT 319 (LC)

IN THE MATTER OF A NOTICE OF REFERENCE
UT Neutral citation number: [2011] UKUT 319 (LC)Case No LCA/509/2010Venue BETWEEN (1) DERYCK EDWARD WRIGHT, (2) IRIS DOROTHY WRIGHT, (3) AVIVA INSURANCE UK LIMITED Claimants, and, HORSHAM DISTRICT COUNCIL Compensating, Authority, Re: 25 The Fieldings, Southwater, Horsham, West Sussex, RH13 9LY, Before: N J Rose FRICS, Sitting at: 43-45 Bedford Square, London, WC1B 3AS, Robin Green, instructed by Plexus Law of Colchester for the Claimants, Celina Colquhoun, instructed by Solicitor, Horsham District Council for the Compensating Authority., The following case is referred to in the decision:, Bell v Canterbury City Council (1988) 56 P & CR 211, The following cases were also cited:, Bollans v Surrey County Council (1969) 20P & CR 745, Fletcher v Chelmsford Borough Council (1992) 63 P & CR 312, Buckle v Holderness (1997) 71 P & CR 428, Halifax General Insurance Services v Teignbridge District Council [2011] UKUT 213 (LC), Factorset Ltd v Selby District Council [1995] 2 EGLR 190, DECISION, Introduction
Between
Wright & AnorHorsham District Council
Date 20 July 2011
[1]This is a claim for compensation under section 203(1)(a) of the Town and Country Planning Act 1990 for losses alleged to have been incurred in consequence of the refusal of consent required under a tree preservation order. The compensating authority is Horsham District Council who, on 16 September 2005, refused consent to fell three oak trees, included within the Horsham District Council Mill Straight, Southwater 1975 Tree Preservation Order (the 1975 TPO) and described therein as T1, T2 and T3. The claimants are Mr Deryck Edward Wright and Mrs Iris Dorothy Wright, the owners of a two-storey detached house known as 25 The Fieldings, Southwater, Horsham (the subject property) constructed to the north of T1-T3, and their insurers, Aviva Insurance UK Limited (Aviva).[2]The claim is for the cost of underpinning works to the foundations of the subject property, which it is agreed totalled £23,251.25. Mr and Mrs Wright also seek the sum of £750 for distress and inconvenience. The compensating authority says that no compensation is payable.[3]Mr Robin Green of Counsel appeared for the claimants. He called two witnesses of fact, namely one of the claimants, Mr Wright, and Mr Patrick Isaacs, a loss adjuster employed by Cunningham Lindsey, who were instructed by Aviva to deal with Mr and Mrs Wright’s insurance claim in October 2003. Mr Green also called expert evidence from Dr Martin Dobson BSc (Hons), DPhil, an arboricultural consultant based in Bordon, Hampshire, and Mr Bret Champion BEng (Hons), CEng, MIStructE, ACILA, the managing director of Pyle Consulting of Reigate.[4]Counsel for the compensating authority, Miss Celina Colquhoun, called expert evidence from two of the authority’s employees. They were Mr William Jones, the arboricultural officer in development management, who holds the Royal Forestry Society’s certificate in arboriculture, and Mr David Starr BSc, MRICS, MBEng, the authority’s principal building control officer. Facts[5]In the light of two statements of agreed facts and the evidence I find the following facts. The subject property was erected in 1976 and was purchased by Mr and Mrs Wright in the same year. To the east (the left hand side of the property as viewed from The Fieldings) was a garage. In about 1983 the garage was converted to a side extension comprising a dining room/study and two additional bedrooms above. A new tandem garage was added at the side.[6]The neighbouring property to the east, No. 24, suffered subsidence in 1996 . This was attributed by the consulting engineers appointed on behalf of the owners’ insurers to a row of nearby oak and ash trees.[7]In 1998 Mr Wright noticed that the corner of the garage had subsided. Remedial works, including partial underpinning of the garage at the rear, were carried out in around October 1999. Following an application by Mr Wright dated 28 August 2001, consent was granted on 23 October 2011 to fell a small oak tree and to reduce the crowns of T2 and T3 by 20%.[8]In September 2003 Mr Wright noticed that some previous hairline cracks in the property had become much worse. Externally there was a crack in the brickwork in the centre of the rear of the house. Internally there were cracks in the kitchen and dining room on the ground floor and in two bedrooms and an en suite above. Mr Wright notified the building insurer of the cracks and Cunningham Lindsey were instructed. Mr Isaacs, who is a Chartered Engineer, a Member of the Institute of Civil Engineers and a Chartered Loss Adjuster, visited the property on 1 November 2003. He wrote to Mr and Mrs Wright on 11 November 2003 and advised that:
“I am of the opinion that damage to the rear elevation has probably been caused by shrinkage of the clay subsoil supporting the foundations of your house, exacerbated by moisture extraction by nearby vegetation, in particular the oak trees beyond the rear boundary. It is possible some of these trees may need to be removed to prevent further damage occurring.”
[9]Mr Isaacs instructed CET Group Ltd to carry out site investigations, namely 2 trial pits in the garden close to the rear elevation of the house and 2 boreholes, one in the rear garden and one in the front garden. In addition Cunningham Lindsey carried out a programme of crack monitoring at the house. Two cracks were monitored, crack 1 at damp proof course level and crack 2 above the patio doors. A firm of arboriculturists, OCA UK Ltd, were instructed to report on the effects of vegetation surrounding the property.[10]Following receipt of reports from CET and OCA, on 11 May 2004 Mr Isaacs prepared an engineering appraisal report on the claim. It included the following observations:
“SITE INVESTIGATIONS The ground investigation was carried out by the CET Group under our supervision and for details, please refer to the attached factual data. Two trial pits were excavated at the rear of the property as shown on the attached sketch. The pit at the rear right corner was extended by hand auger. A further borehole was augered in the front garden, to act as a control. The investigations reveal that the property has been provided with traditional concrete strip foundations, 200mm thick, the under side located at a depth of 1.10m below ground level. The supporting subsoil was a stiff to very stiff clay material, classified as highly shrinkable. Numerous roots were recovered from beneath the foundations to the area, these emanating from the Oak trees beyond the rear boundaries. Laboratory analysis of the soil samples reveal that the clay in the area of damage was approaching desiccation. In addition, moisture content values from the control borehole, at the front of the property, were significantly higher than those obtained from the area of damage. MONITORING A regime of crack monitoring has been established. CAUSE OF DAMAGE The investigations have confirmed subsidence damage due to shrinkage of the underlying clay subsoil. The water demands of the Oak trees will be a major influence in this regard. RECOMMENDATIONS We appointed our arboriculturists, OCA UK Ltd, to report on the effect of vegetation in the vicinity of the property. A copy of their report is attached. They have recommended removal of several trees and they will now liaise with all parties to ensure these works are implemented as soon as possible. Repairs to the superstructure, incorporating masonry reinforcement as appropriate, can proceed in the Summer of 2004 once the clay subsoil has rehydrated and stabilised and following tree removal.”
[11]On 28 April 2005 arboricultural consultants Marishal Thompson and Co submitted an application to the compensating authority, as local planning authority, on behalf of the owner of 29 The Fieldings, four doors west of the subject property. The application was for consent to fell an ash tree at the rear of No.29. Site investigation data was provided in support of the application. It included the results of soil suction tests, which revealed significant desiccation below the 1.2m deep foundations in BH1 and BH2 to a depth of 3m and particularly severe desiccation in BH4 to about 4m. Ash roots were found below foundation depth in BH3 to a depth of 1.2m. On 20 July 2005 consent to fell the ash tree was refused because:
“insufficient evidence has been submitted to satisfactorily demonstrate a causal link between possible root action of the ash tree in question and the alleged structural damage to the dwelling.”
[12]On 28 June 2005 OCA submitted an application for permission to fell T1, T2 and T3. Enclosed with the application were Mr Isaacs’s engineering report dated 11 May 2004, CET Group’s factual report of investigation including laboratory soil test results and root identification certificates, a site plan locating vegetation, the latest crack monitoring results and an evidential assessment summary.[13]In a letter accompanying the application, OCA submitted that they had demonstrated that tree roots had encroached the underside of the foundations and that damage to the subject property had resulted from that encroachment. The following reasons for the application were given:
“(i) The above tree works are proposed as a remedy to the differential foundation movement at the above address and to ensure the long-term stability of the building. (ii) The above tree works are proposed to limit the extent and need for expensive and disruptive engineering repair works. (iii) The above tree works are proposed to limit the duration of any claim period and therefore allow the landowner his right to the peaceful enjoyment of his property. (iv) It is the case that an alternative to felling such as pruning or significant pollarding of the tree(s) would not provide a reliable or sustainable remedy in this case. We do not consider that any other potential means of mitigation, such as root barriers, would be effective or appropriate in the circumstances. (v) Estimated repair costs will vary between £10,000 and £32,000, depending upon whether the trees can be removed or have to remain.”
[14]A Mr Handley, the owner of No.26, immediately to the west of the subject property, wrote to the local planning authority about the application to fell T1-T3 on 23 July 2005. The letter included the following: “As you may be aware, my own property … was underpinned in 1999. In the final report that I have in my possession, the cause of the ‘movement in the property’ was not attributed to the trees, but to erosion of soil by leakage from the defective drainage system. In the initial investigations a report was produced by Mr Timothy Laddiman of Chris Yarrow & Associates, which stated as follows: ‘ In considering whether removal of the trees would provide the required recovery and stabilisation, there is still the problem of obtaining permission for felling TPO covered trees, one being a third party tree. There may also be the slight risk of heave movement occurring, given the relative ages of the tree to the buildings, though the risk is lower than if the trees were large mature specimens. There is insufficient data available to make a full assessment of the heave potential, and if this option were pursued, the insured and insurers would need to be aware of, and accept the risk of heave occurring.’’’[15]Mr Jones inspected the subject property on 1 September 2005. His assessment was dated 13 September 2005. It recommended that the application be refused for the following reasons:
“1. Insufficient evidence of differential foundation movement at the site has been submitted. It is also not accepted that the felling of the trees would necessarily ensure the long-term stability of the building. 2. The Council does not accept that removal of the trees would necessarily limit the extent and need for expensive and disruptive engineering works which may require to be undertaken in any event, or that this is suitable or sufficient justification for the removal of protected trees of amenity value, this being contrary to policy EDC 28 of the Local Plan. 3. The Council does not accept that limiting the duration of any claim period is suitable or sufficient justification for the removal of protected trees of amenity value, this being contrary to policy EDC 28 of the Local Plan. The Council also does not accept, from the evidence submitted with the application, that the felling of the trees would necessarily result in the landowner enjoying his right to the peaceful enjoyment of his property. 4. The Council is of the view that, as insufficient evidence to support the application has been submitted, felling the trees on the grounds that there is no other option is inappropriate. 5. It is not considered that the attested increase in estimated repair costs is sufficient justification for the removal of protected trees of amenity value, this being contrary to policy EDC 28 of the Local Plan.”
[16]On the same day, a member of the Colchester office of Cunningham Lindsey advised OCA that it was considered that their file “did not have enough strong evidence to win an appeal.’’ Formal notice of refusal of consent to fell was dated 16 September 2005. The reasons for refusal were identical to those recommended in Mr Jones’s assessment.[17]Mr Isaacs inspected the property again on 19 October 2005. He noted that further damage had occurred since his previous visit in November 2003. The crack monitoring showed ongoing movement. He concluded that, in order to stabilise the property it would be necessary to underpin the rear to a depth below the influence of the oak roots. He discussed with Mr Wright the possibility of appealing against the refusal. It was decided to press ahead with the repair works, bearing in mind that the claim had been made more than 2 years earlier, that it would take between 1½ and 2 years for an appeal to be determined and that the success rate in such appeals was not high.[18]A claim for compensation consequential on the refusal of consent was submitted by Cunningham Lindsey on 5 June 2006. Underpinning to the eastern and rear (southern) elevations was carried out between 5 and 16 June 2006.[19]On 28 December 2007 a CCTV survey of the drains at the subject property was carried out by 1 st Clear Flow Limited of Worthing. The written report on this survey, and the accompanying DVD, were produced by Mr Wright shortly before commencement of proceedings on the first day of the hearing. Expert evidence for the claimants Dr Dobson[20]Dr Dobson was instructed by the claimants’ solicitors in a letter dated 11 February 2011 to prepare an expert report setting out his opinion on arboricultural issues relating to alleged subsidence at the subject property. He said that in order to distinguish subsidence damage from other forms of structural damage it was usually necessary to demonstrate that the damage arose in late summer (when soil drying reaches its peak), that soil below foundations was shrinkable clay, that foundations were not sufficiently deep to withstand the foreseeable influence of nearby trees and that the building was within the “zone of influence” of one or more trees. Further, it was important to demonstrate that roots of such trees were present below foundations and that the soil affected by such root intrusion was drier than would otherwise be the case if there were no roots. Finally, it was necessary to demonstrate that the pattern of building movement or crack damage was seasonal and cyclical, that is, cracks opened during the drier summer months and closed during the wetter winter months. Or, in the case of level monitoring, the building moved downwards in the summer and upwards in the winter.[21]The evidence in this particular case was that subsidence damage had previously occurred at 25 and 26 The Fieldings which had necessitated underpinning in 1999. It was therefore known that the site was vulnerable to subsidence damage. New damage to the main part of the house at the rear occurred following the exceptionally dry summer of 2003. This was recognised as being an “event” year, with the cost of subsidence insurance claims being double that in 2002. The damage became apparent as cracks, which appeared suddenly at the end of the summer of 2003, coinciding with peak soil drying associated with trees. The site investigations demonstrated that soil below foundations was high to very high shrinkage clay which was infiltrated by tree roots. Samples of these roots were identified as oak. Tests carried out on soils recovered from below foundation depth revealed that the clay was drier at the rear of the property, in the area affected by tree roots, than at the front. The soil was also stiffer and had a higher penetration resistance at the rear, near to the trees. Comparison of moisture content with 0.4 x liquid limit (a commonly adopted rule of thumb for determining the presence of significant desiccation) further confirmed that the soil at the rear had become desiccated.[22]The crack monitoring results confirmed a seasonal and cyclical pattern of movement. The subsidence damage that had occurred in 2003 recovered during the winter of 2003/4 resulting in crack closure. Since 2004 was not especially dry, crack 1 did not open significantly during summer 2004, although crack 2 did open during the summer by approximately 0.5mm.[23]In relation to “zone of influence” oak was a high water demand species according to the National House Building Council (NHBC) classification. Such trees had the greatest potential for causing subsidence damage over the greatest distance.[24]The foundational piece of work detailing cases where tree roots had been implicated in subsidence damage to buildings was known as the “Kew Root Survey”. This was a standard reference to which arboriculturists and others referred when considering distances within which buildings on clay soils might be at risk from the influence of trees. Maximum distances from trees to buildings in which damage had been recorded were given. The maximum tree-to-damage distance for oak was 30m. By comparison, the distances from the subject property to the three trees in question were 12.5m (T1), 10.5m (T2) and 9m (T3). The subject property was therefore within the potential zone of influence of all three trees.[25]Guidelines produced by the NHBC gave recommendations on when foundation design for new buildings on shrinkable clay soil should be deepened to take account of nearby trees. The guidelines used several interacting factors including tree species, water demand, tree height and distance from a building, and the shrinkability of the soil, to predict risk to foundations. Whilst the guidelines were properly intended for determining appropriate foundation depths for new houses, they could also be usefully applied to assess the adequacy of existing foundations near to trees.[26]Appropriate foundation depths were calculated on the basis of water demand, the height of the tree and the distance between the foundations and the tree. In calculating how deep the foundations would need to be (assuming the building were to be constructed today) the NHBC generally recommended that the mature height of a tree should be used in making this calculation, and for oak that was 20m. On the basis that foundations across the rear of the building were 1.1m, the zone of influence of the oaks would be equivalent to 1.2 x height, that is 24m. It was therefore apparent that the foundations were too shallow to withstand the foreseeable influence of the oak trees T1-3, which were located between 9 and 12.5m from the property.[27]In Dr Dobson’s view there was other information within the contemplation of the compensating authority that should have been taken into account when making a decision whether or not to permit the felling of T1-T3. In particular the history of subsidence problems locally (Nos. 24, 25, 26 and 29) and the fact that the supporting evidence for the contemporaneous 2005 application at No.29 revealed clear evidence of severe desiccation below foundations at the rear.[28]In summary, he believed that the evidence in the contemplation of the compensating authority was more than adequate to demonstrate on the balance of probabilities that the subject property suffered from subsidence caused by one or more of T1–T3. He thought that the principal tree causing damage was likely to have been T2, since it was closest to the area of damage, but he considered that T1 and T3 were also likely to have been a material cause.[29]Dr Dobson referred to the guidance given in Tree Preservation Orders: A Guide to the Law and Good Practice . This stated at paragraph 14.7 that:
“In dealing with an application for consent under a TPO the LPA are advised to consider whether any loss or damage is likely to arise in consequence of their decision during the following 12 months, having regard to the reasons given for the application and any reports or other documents submitted by the applicant in support of those reasons.”
[30]OCA clearly stated that the reason for the application to fell the three trees was “differential movement and subsequent damage consistent with tree-related clay shrinkage subsidence”. The claim for compensation was therefore directly related to the application. Dr Dobson concluded that the evidence supplied with the application was sufficient to demonstrate on the balance of probabilities that the oaks were responsible for subsidence damage. Therefore, in the absence of removal of the cause of damage, it was likely that crack damage would continue, as indeed it had. It was well known to arboriculturists that if an arboricultural solution to a subsidence problem was not implemented, the next course of action to stabilise a building and nullify a nuisance was usually to underpin. It appeared from the last paragraph on the first page of the notes relating to the application prepared by Mr Jones that he was familiar with the use of underpinning to mitigate a nuisance to which neighbouring trees may have contributed. It was therefore clearly within the compensating authority’s contemplation that underpinning could well be necessary.[31]The London Tree Officers Association had produced a “Risk Limitation Strategy for Tree Root Claims”, 1994, which gave advice to tree officers as to how to reduce the costs of tree root claims. The guide made it clear that claims against councils for underpinning and superstructure repairs often arose because of a reluctance on the part of councils to permit pruning or felling of trees. It therefore advised that:
“In all but a few cases tree pruning will mitigate the significant costs associated with tree root claims. Moreover, regular tree pruning and/or selective tree removal (and replacement) may prevent these claims arising in the first instance.”
Dr Dobson had no doubt that Mr Jones would have been aware of this publication and it should have been a material consideration in his decision-making process.[32]Dr Dobson disagreed with Mr Jones’s assumption that underpinning might be needed in any event even if the oak trees were removed. He explained that heave was the upward movement of a building that occurred when a desiccated soil rehydrated. Heave could be divided into two categories, heave and recovery. The proper use of the term heave was when a building had been constructed on a persistently desiccated site. When the tree which caused the desiccation was removed the building was lifted differentially beyond its construction levels, resulting in progressive crack damage that might take place over several years depending on how quickly the soil rehydrated. Underpinning was often necessary in these circumstances, but having said that the occurrence of heave damage was comparatively rare compared to subsidence damage.[33]Recovery, on the other hand, was when a building recovered from a tree-related soil moisture deficit which arose after the construction of a building. If the deficit was not particularly severe then the soil might recover fully, and usually did, during a single winter and no such substructure works would be necessary when a tree was removed. But if the soil moisture deficit became severe and persisted from one summer to the next then, once the cause of that soil drying was removed, it might take an unacceptably long term for the soil to recover and for the building to stop moving. In these circumstances underpinning might be appropriate.[34]Dr Dobson said that he had seen no evidence to suggest that the subject property was built on a desiccated site. If it was then it might be expected that some heave damage would have occurred immediately following the root severance that must have resulted from the 1999 underpinning, or alternatively immediately after the oaks were pruned in 2001. But no damage was recorded after 1999 until the hot dry summer of 2003.[35]During the summer of 2003 cracks 1 and 2 suddenly appeared and progressively opened in response to drying of the clay soil. The cracks had not been there before and consequently were solely caused by the influence of oaks in that summer. During the winter both cracks closed and crack 1 remained closed throughout the following summer and winter. That pattern was important to note, because if there had been persistent desiccation of the soil crack 1 would not have fully closed and it is likely that, in the absence of any summer opening in 2004, the crack would have closed further during the winter of 2004/5. The fact that the crack did not, and in all probability could not, close any further indicated that there was no persistent soil moisture deficit and therefore there was no chance of heave movements if the oaks were felled.[36]Dr Dobson said that the evidence gathered after the determination of the 2005 application in terms of crack monitoring indicated that the building was continuing to experience movement, with new cracks appearing and existing cracks opening up by up to 2mm during 2005. It was therefore appropriate to underpin the building to bring about stability. Mr Champion[37]Mr Champion was instructed by the claimants’ solicitors on 11 February 2011 to prepare an expert report, setting out his opinion whether any or all of the three oak trees had been a material cause of the damage to the subject property. He was also instructed to advise on the question of building costs, which are no longer in issue.[38]Mr Champion reproduced extracts from the documents entitled “Claim Details” and “Engineering Appraisal Report” which had been prepared by Cunningham Lindsey in November 2003 and May 2004 respectively. He considered that this evidence confirmed that cracking and distortions as a result of subsidence of the clay substrata beneath the rear elevation of the subject property had occurred during the summer of 2003.[39]The trial pit investigations undertaken by CET Group showed that the foundation to the rear elevation extended to a depth of 1.1m below ground level. Mr Champion quoted from Building Research Establishment Digest 240 entitled “Low Rise Buildings on Shrinkable Clay Soils”. This indicated that the foundation to the rear elevation was founded at a depth at which ground movement would not occur as a result of seasonal wetting and drying and the influence of minor vegetation.[40]It was therefore necessary to identify another factor as being the effective cause of the differential foundation movement of the rear which first occurred during 2003 and continued thereafter as confirmed by the crack monitoring. In Mr Champion’s opinion, the partial underpinning carried out in 1999 would not have caused the differential foundation movement. The foundation to the original house had provided adequate support since it was constructed in 1976. Apart from the influence of the oak trees there would have been no reason for differential movement to occur.[41]Mr Champion summarised the results of laboratory testing of soil samples recovered during the site investigations in December 2003. In his opinion the moisture content and shear strength profiles confirmed desiccation of the clay beneath the foundations to the rear for the depth of the roots as confirmed in the boreholes. This opinion was based on the following facts. Firstly, the moisture content at 1.5m below local ground level in borehole No.1 was significantly less than in borehole No. 2. Secondly, the shear strengths at 1.0m, 1.5m and 2.0m for borehole No.1 was significantly greater than in borehole No. 2.[42]Mr Champion drew attention to the evidence of Mr Isaacs to the effect that the depth of the underpinning had to be increased on site due to the level of root activity. It followed, he said, that roots extended to depths greater than that noted in borehole No. 1 (1.8m). This would explain why moisture contents at 2.0m and 2.5m in borehole No.1 were significantly less than the moisture contents at these levels in borehole No.2. Moreover, the greater depth of roots would explain why the shear strength at 2.0m in borehole No.1 was higher than that at 2.0m in borehole No.2 . Thus, the moisture content profiles and the shear strength testing confirmed desiccation, not just for the depth of roots noted in the boreholes but also for the depth of roots confirmed during the underpinning. For completeness Mr Champion quoted the relationships for determining whether a soil was desiccated suggested in a paper entitled “The Influence of Vegetation on the Swelling and Shrinking of Clay Soils in Britain.” He considered, however, that comparing moisture content profiles and shear vane profiles with a control borehole was a more reliable method of determining desiccation than applying such relationships.[43]Mr Champion disagreed with Mr Starr’s suggestion that underpinning would have been required if the oak trees had been removed. He said that he had undertaken a heave analysis in accordance with the procedure described in BRE Digest 312 entitled “Desiccation of Soils”. This analysis was for the full depth of desiccation as confirmed by the moisture content profiles (2.75m) and not the depth of the roots noted in the boreholes (1.8m maximum). It indicated that the maximum heave would have been 48mm. The crack width monitoring confirmed vertical closure of cracking up to 5.1mm. In addition to cracking, the 2003 event of subsidence would have caused distortions to the property which would also have been corrected as a result of rehydration during the winter of 2003/4. That is, heave recovery as a result of the 2003 subsidence would have been greater than 5.1mm. Taking into account the closure of cracking and the correction of distortions, Mr Champion considered that the permanent moisture deficit prior to the 2003 subsidence would have resulted in a theoretical potential heave less than 40mm. In his experience dealing with hundreds of subsidence damaged properties over many years, he did not consider an impartial expert with similar experience could conclude that potential heave of less than 40mm would warrant underpinning if the oak trees were removed.[44]In support of this conclusion, Mr Champion pointed to Mr Wright’s evidence that the oak trees were much smaller when he purchased the property than they were now. It followed that any permanent moisture deficit caused by the trees prior to construction would have been minimal. Removal of the trees would only have addressed the moisture deficit since construction of the house and would not have caused a problem of long term heave damage.[45]Finally, Mr Champion commented on the relevance of the NHBC Standards Chapter 4.2 “Building near Trees.” Based on these standards the theoretical zone of influence of T1 – T3 had extended under the foundations to the rear elevation at the time of OCA’s survey in January 2004. The ground investigations at that time showed roots extending to a depth of 1.8m below local ground level at the rear elevation and roots were confirmed to extend deeper during the underpinning. The depth of the roots was therefore in line with the theoretical zone of influence of the oaks.[46]Mr Champion also prepared an addendum report dated 13 July 2011. This report took account of the fact that different heights of T1-T3 at various dates had now been agreed by the arboricultural experts from those detailed in OCA’s report and that there had been considerable discussion between the arboricultural experts regarding the monitoring. In the light of this additional information Mr Champion did not consider that there was a problem of permanent moisture deficit of the soil beneath the foundations in 1976. Therefore there would not have been heave of the supporting soil beneath the foundations as a direct result of the oak trees being older than the house. In view of this; the fact that there was no evidence that damage/distortions had occurred as a result of subsidence between construction in 1976 and the damage occurring in 2003; and the fact that the 2003 damage had closed up, Mr Champion remained firmly of the opinion that heave would not have caused damage to the subject property if the trees had been felled. He pointed out that there were alternative procedures for calculating the theoretical maximum potential heave. There was, however, no need to undertake further site investigations and/or analysis of testing. Sufficient evidence had been gathered to prove that heave would not be an issue.[47]Mr Champion also prepared a sketch which he said demonstrated that the underpinning would have severed any roots from the oak trees which extended under the building envelope. If heave had been a problem following installation of the underpinning and severance of the roots, it would have caused distortions to the property including upward movement of the concrete ground bearing slab and outward movement of the rear elevation. This would have happened because the rear elevation would have been “locked” vertically into position by the underpinning. Since underpinning was installed in 2005, if heave was likely to have been a problem it would have resulted in such damage being manifest by 11 July 2011, when he re-visited the property. He had specifically looked for evidence of such heave damage, but could find none. This reinforced his view that if the trees had been felled heave would not have caused damage.[48]Finally, Mr Champion produced details of the monthly rainfall between 2001 and 2009. He compared this information with the crack monitoring records for station 1. He said that there was exceptionally good correlation between the monitoring and the rainfall. This showed that the movement across the cracks was cyclical/seasonal, and such movement happened as a result of the influence of trees. Expert evidence for the compensating authority Mr Jones[49]Mr Jones was the officer who dealt with the claimants’ application to fell T1-T3. He said that, in cases proposing the felling of a tree or trees, the Government guidance set out in “ Tree Preservation Orders – A Guide to the Law and Good Practice ” (DETR, March 2000) was to determine whether to grant consent to the felling based upon an assessment. “(i) of the tree or woodland and the likely impact of the proposal on the amenity of the area, and (ii) in the light of their assessment at (i) above, to consider whether or not the proposal is justified having regard to the reasons put forward in support of it.” The guidance stated that “in general terms, it follows that the higher the amenity value of the tree or woodland and the greater the impact of the application on the amenity of the area, the stronger the reasons needed before consent is granted.” The reader was also advised “to consider whether any loss or damage is likely to arise if consent is refused or granted subject to conditions.”[50]Mr Jones said that, in clay soils, trees could be responsible for structural defects as a result of their roots abstracting moisture from the sub-strata, causing desiccation and resultant shrinkage. All trees were known to have a “zone of influence”, within which their roots could be responsible for this. If a dwelling was within this zone, on clay soils, structural defect could occur. There were, however, other reasons for foundation movement, such as excessive load or defective material beneath the foundations; collapse of mine workings or other related works; slope instability; fluctuation in ground water levels; and leaking drains causing washing out of fine particles from the soil. In addition, in cases where it was suggested that trees were causing subsidence it was also appropriate to examine any previous subsidence events at the property which could be a causal factor.[51]The most common way of demonstrating that subsidence was being caused by a tree was by showing a clear cyclical pattern of foundation distortion. In such cases results of measurements would show a clear upward movement of the foundations during the winter months, when the soils were rehydrating and trees dormant, followed by a clear downward movement during the summer, when ground evaporation and the water demand of trees were at their highest and rainfall low. Such evidence, however had to be considered with care. The onus of proof was on the applicant. In assessing whether that onus had been discharged, it was also necessary to consider any other factors which might call into question an applicant’s claim that damage had been caused by trees. In making such an assessment, Mr Jones said that he would refer to the NHBC document “Building near Trees” which provided guidance on the water demands of different tree species. It also explained the principle of the zone of influence, that is the radius of an imaginary circle around the tree within which it was known that roots might have an influence upon the surrounding soils.[52]Mr Jones would also take guidance from “Tree Root Damage to Buildings” (Biddle, 1998), the authoritative work on the subject. In assessing the likely involvement of trees in a case of differential foundation movement, Biddle placed principal emphasis on the need to make a careful analysis of the movements of any property which had suffered subsidence, as without this information the involvement of nearby trees could not be verified. Biddle advised that, although there were several ways of measuring structural defect in a building, the use of a level distortion survey was by far the most effective. He noted that “a level distortion survey provides a very effective method of determining the extent of differential movement which has occurred some time in the life of the building. It should be an essential preliminary part of any investigation”. He added:
“as the underlying causes of any damage are the changes in foundation levels which are occurring, level monitoring is by far the most valuable technique, and should be an essential part of almost all investigations.”
[53]As well as level monitoring, Biddle considered the use of crack monitoring, the ongoing measurement of the pattern of cracks in the superstructure of the building. However, he advised caution in relying on such measurements, noting that “many engineers rely on these patterns of crack damage as the sole means of diagnosing the building movements which have occurred. Although in some cases this may be sufficient, in many cases it is inadequate or even misleading”. He also noted that, in some cases, reliance on this information “had led to serious errors in remedial work.” In conclusion, Biddle advised that:
“the reaction of cracks to foundation movement can be erratic, and excessive reliance on crack monitoring is often misleading. For this reason crack patterns should be studied and analysed, but reliance should not be placed on them as the sole method of diagnosis.”
[54]Mr Jones said, that following receipt of the claimants’ application, he had inspected the site on 1 September 2005. He noted that the three oak trees were unusually compact as a result of previous reductive surgery. Otherwise they appeared to be in good health, showing no sign of serious structural defect. He noted that whilst the trees had moderate to high amenity value, they also “neatly delineate(d) the countryside to the south from the residential area”, were “clearly visible” from The Fieldings, despite being sited to the rear of No.25 and other neighbouring dwellings, and provided “a much needed greening and softening of the estate.” He concluded that they were well worthy of retention and, in accordance with the DETR Guidance, a relatively high level of justification for their removal was required.[55]Taking all the evidence together, Mr Jones noted that the following factors appeared to provide at least circumstantial evidence of the likely contribution of the trees as the material cause of the structural defect to the building: the building was sited on clay soils; the soils exhibited high plasticity levels; the building was sited within the zone of influence of the three trees the subject of the application; there was some evidence of a cyclical pattern of movement as indicated by the submitted crack monitoring data; roots from oak trees had been found close to, or beneath the building; and the comparison between the soil moisture levels and shear strength profiles of samples taken from the front of the house, out of range of the trees, and from the rear indicated a degree of soil desiccation in the area closer to the trees.[56]In Mr Jones’ view, however, these points did not provide conclusive evidence to substantiate the claim that the trees were the cause of the recorded subsidence event. Nor did the monitoring results show a conclusive cyclical pattern which must have been caused by the obstruction of moisture by vegetation. Not only was there no levels distortion survey, but the far less reliable crack monitoring results were themselves inconclusive. Moreover, he considered that insufficient evidence had been submitted to eliminate, on the balance of probabilities, other quite possible causes for the structural defects. These were: defective drainage; the possible effects of the recent pruning works to two of the trees and the removal of another; the likely high levels of rigidity in the building itself, given its age, and how natural variations in temperature and moisture underground might lead to variations in expansion and contraction; how this might have been amplified, or worsened, by the partial underpinning undertaken in 1999 and whether those works in themselves could have caused the problem.[57]Mr Jones therefore concluded that the pattern of cyclical movement noted in the crack monitoring results was inconclusive at best, and could be explained by other factors which the claimants had failed to take into account. Given the moderate to high amenity value of the trees, and paying due regard to the Governmental Guidance, he could not recommend the felling of the trees as it had not been shown on the balance of probabilities that the slight structural deficiencies noted had been caused by the trees. In addition, he questioned the suggestion that the felling of the trees would necessarily avoid the need for expensive and disruptive engineering works, if matters were indeed as bad as was being suggested by the claimants.[58]In the course of cross examination Mr Jones said that, if the 1 st Clear Flow report had been available when he was considering the application in 2005, it would have been much easier for him to rule out leaking drains as the cause of the subsidence. In answer to a question from me he said that the results of further crack monitoring between 25 May 2005 and 25 November 2005 (which were not submitted by OCA with the application for permission to fell) showed that it was more likely than not that the oak trees had been responsible for the subsidence in 2003. Mr Starr[59]Mr Starr was not involved in the compensating authority’s decision to refuse consent to fell T1-T3. His knowledge of the subject property related to the Building Regulations application for partial underpinning works submitted on 27 May 1999 and the subsequent Building Regulations application dated 30 May 2006 for the further underpinning works which followed the refusal of consent.[60]Mr Starr said that, having checked the information provided with the 1999 application, he had written to the claimants’ engineers, Dixon Hurst Kemp, on 28 May 1999. He pointed out that the proposed partial underpinning could cause structural problems to the property in the future. He suggested that consideration be given to full underpinning to avoid the possibility of such problems occurring. Dixon Hurst Kemp replied on 8 June 1999. They said that, following investigation of the existing garage and house foundations, they had concluded that only the back of the garage needed underpinning. Nevertheless, they had revised the proposals by reducing the underpinning progressively towards the depth of the existing foundations. Since there were no signs of damage to the house itself they considered that further underpinning was unnecessary.[61]Mr Starr said he had set out his concerns in his letter of 28 May 1999 in order to highlight the potential effect of the proposed works on the rest of the building. A completion certificate was issued because the works were found to pass the minimum standard. Nevertheless, the creation of a more rigid area of support to part of the superstructure rendered the structure around the junction between the existing and underpinned foundations vulnerable to distortion and cracking.[62]Whilst Dixon Hurst Kemp’s revised design included a reduction in underpinning depth between the new work and the existing foundation depths, it did not take into account any future movement in the foundations which might be caused by subsidence. The section of the building underpinned by the works in 1999 had foundations to a depth of 2,700mm, which meant that they would not be affected, or they would be affected differently from the rest of the foundations, by the influence of trees.[63]The amount of disruption to foundations by trees over a period of time depended on the type and proximity of the trees. The amount of water removed from the normal ground moisture content would depend, among other factors, on the age of the tree and its growth rate. Damage to the building could occur at the same rate as ground conditions changed. In other cases foundations or brickwork would resist for some time and then fail in a more dramatic manner. The ability of existing foundations to withstand damage in this type of situation was influenced by such matters as the type of concrete and size of section, as well as the possible propping action resulting from partial underpinning. Having reviewed the evidence submitted by the claimants which suggested that further subsidence had taken place after 1999, Mr Starr concluded that it was possible that the damage caused in 2003 was due in part to the building having been partly underpinned.[64]Assuming the partial underpinning had not contributed to the damage, and that the trees alone were responsible, Mr Starr was firmly of the opinion that underpinning would have been required in any event, even if permission had been granted to remove the trees. This was because, if the trees were affecting the foundations in 2003, then the effect of their removal on the soil would have had to be taken into account and would have required the foundations to be underpinned in a similar fashion to the works actually carried out in 2006.[65]Mr Starr produced a response to Mr Champion’s addendum report. He pointed that, in applying the method set out in BRE Digest 412 to predict heave, Mr Champion had adopted the suggested average Water Shrinkage Factor (WSF) of 4. In Mr Starr’s opinion it was not appropriate to use an average WSF when dealing with an area of Weald Clay, which was liable to large changes in volume due to small moisture changes. He considered that Mr Champion’s assessment was at the bottom of the potential range of heave. The top end of such range would be at least four times Mr Champion’s estimate, namely 144mm compared with 36mm. Even if that figure was an overestimate, there was nevertheless a significant amount of potential heave sufficient to warrant underpinning.[66]In the course of cross examination Mr Starr accepted that, in the light of the evidence which was by then available, he considered that it was the oak trees, and not leaking drains, which had caused the subsidence in 2003. The entitlement to compensation[67]Section 203(1)(a) of the Town and Country Planning Act 1990 (as amended) provides as follows:
“A tree preservation order may make provision for the payment by the Local Planning Authority, subject to such exceptions and conditions as may be specified in the order, of compensation in respect of loss or damage caused or incurred in consequence of the refusal of any consent required under the order.”
[68]The 1975 TPO was in the form of a “1969 Model Order”, that is in the form prescribed by the Town and Country Planning (Tree Preservation Order) Regulations 1969. 1969 Model Orders provide (as does the 1975 TPO under Article 9) that: “any person who has suffered loss or damage in consequence of any refusal … of consent under this Order… shall, if he makes a claim on the authority within the time and in the manner prescribed by this Order, be entitled to recover from the authority compensation in respect of such loss… Provided that no compensation shall be payable in respect of loss or damage suffered by reason of such refusal… in the case of any trees the subject of a certificate in accordance with Article 5 of this Order.” (Such a certificate may be issued by the relevant authority on the basis that it is in the interests of good forestry so to do or that the trees in question are of outstanding or special amenity value. It was not suggested that an Article 5 certificate had been issued in respect of T1-T3).[69]The measure of compensation payable under a 1969 Model Order was considered by the Court of Appeal in Bell v Canterbury City Council (1988) 56 P&CR 211. At 216 Russell LJ said:
“In my view the diminution in the value of the land was a natural and probable consequence of the refusal of consent, within the contemplation of the local authority refusing consent. It was not too remote and was, therefore, recoverable.”
[70]At 219 Slade LJ observed:
“The only question therefore is whether, on its true construction, Article 9 does render compensation payable in respect of such depreciation. The language of the Article is very broad and, subject to what is said below, I can see no sufficient grounds for restricting its meanings so as to exclude compensation in respect of this particular category of loss.”
Issues The issues between the parties are these: (1) In deciding whether the cost incurred in underpinning the subject property was the natural and probable consequence of the compensating authority’s refusal of consent, within the contemplation of the authority when refusing consent and not too remote, can the tribunal have regard to all the evidence before it, or is it restricted to considering the evidence relied upon by the claimants at the time of the application, together with any other evidence available to the council at that time? (2) In light of the answer to issue 1, is the admissible evidence sufficient to establish that the damage to the subject property was caused by one or more of the three oak trees, T1-T3? (3) Was underpinning the natural and probable consequence of the refusal of consent? (4) Was underpinning within the contemplation of the compensating authority when it refused consent? (5) Would underpinning have been required in any event as a consequence of the trees being removed? (It is agreed that underpinning would have been necessary if the trees had remained in place and that, when considering this issue, the tribunal is entitled to have regard to all the relevant evidence before it). (6) Is compensation payable in respect of distress and inconvenience and if so, how much? Conclusions Issue 1 – the extent of the evidence to be considered[71]Mr Green submitted that, as the purpose of the compensation provision in Article 9 was to compensate persons who suffered loss “in consequence” of the refusal of consent, it was difficult to understand why the tribunal should be limited to a consideration of the evidence before the compensating authority at the date of refusal. He accepted that, in looking at what was in the contemplation of the authority at the time consent was refused, the focus would inevitably be on the material before the authority, but in assessing whether in fact the trees were the likely cause of the damage, or whether the underpinning subsequently undertaken was a reasonable response to the refusal of consent, it would be nonsensical to ignore evidence arising after the decision to refuse consent. 72 Miss Colquhoun’s submissions on this issue were these: In order for something to be in the contemplation of an authority it needs to have been raised by the applicant in his application for consent, together with proof that it was a natural and probable consequence. In order to meet the relevant test, therefore, the claimants needed to show the tribunal that the evidence provided to the council at the time of the application was sufficient to prove that the three trees were the cause of the damage to the claimants’ property and therefore that works required to put that right in the event of a refusal were reasonably foreseeable.[73]I am inclined to accept the submissions of Mr Green on this issue, but it is not necessary for me to decide the point. That is because, for reasons which I shall explain under issues 2 and 3, I am satisfied that the information before the compensating authority when it refused consent was entirely sufficient to establish that the damage had been caused by trees and that underpinning would be necessary. Issue 2 – Causation[74]It is common ground that, in deciding whether the trees were responsible for the subsidence in 2003, the test to be applied is the balance of probabilities. That is not the test used by Mr Jones when he recommended that permission to fell should be refused. In paragraph 2 of his assessment of the application Mr Jones said:
“no evidence has been submitted to satisfactorily demonstrate, beyond a reasonable probability , a causal link between desiccation of clay soil as a result of water uptake by the trees in question and the attested property damaged… This [crack monitoring data] is not considered to be evidence anywhere close to being conclusive that the property is suffering from a cyclical pattern of movement consistent with vegetation.” (Emphasis added).
[75]In my judgment, if Mr Jones had applied the proper evidential test, he would inevitably have concluded that the claimed causation had been proven. The following evidence all pointed to tree root damage:(i) In the Summer of 2003 the compensating authority received a noticeably increased number of applications to remove trees.(ii) There was a particular volume of such applications in relation to trees in Southwater.(iii) Southwater was noted for tree root related subsidence.(iv) The damage was within the zone of influence of all three trees in question.(v) Roots of oak trees, which have a high water demand, were found following ground investigations close to the rear of the property.(vi) Soil taken from BH1 (close to the rear elevation) as compared with the samples from BH2 at the front of the house, showed desiccation. Desiccation in clay soils can result in subsidence of the ground and damage to buildings.(vii) In cross examination Mr Jones accepted that he could not think of an explanation for the 5mm closure in winter of the vertical crack width at the rear right corner at damp proof course level (station 1) which was consistent with the remaining evidence, other than that the subsidence was tree related.[76]In his expert report Mr Jones placed particular emphasis on the advice from Biddle, to the effect that crack monitoring data should be treated with caution, and on the letter from Mr Handley, which suggested that the structural problems at No.26 had been caused by defective drainage. I do not attach any significant weight to either of these factors. Biddle warned against relying on crack monitoring as “the sole method of diagnosis” but, as is clear from paragraph 75 above, the crack monitoring was far from being the only evidence which pointed to the responsibility of tree roots for the damage. As for Mr Handley’s letter, it contained inconsistent information. Although the final report apparently attributed the building movement to defective drainage, Mr Laddiman referred to the possibility of heave movement, which would not have arisen if there was a leaking drain. In response to a question from me Mr Jones said that he had been aware of this inconsistency at the time, but he had not thought it necessary to ask Mr Handley to clarify the position. That answer did not suggest that an objective approach had been taken to the ascertainment of the cause of the subsidence.[77]In concluding that, on the balance of probabilities, the damage to the subject property was caused by tree roots, I have not overlooked the agreed fact that the previous partial underpinning could have caused a hard spot and as a consequence it could have exacerbated the damage. There was little evidence that this was in fact the case and it does not detract from the fact that, but for the trees, there would have been no damage at all. Issue 3 – was underpinning the natural and probable consequence of refusal?[78]Miss Colquhoun submitted that the compensating authority was in any event not liable to pay compensation on two grounds, both of which question whether underpinning was the natural and probable consequence of the refusal of consent. Firstly, she submitted that, since none of the subject trees were within land owned by the claimants, obtaining consent to fell the trees would not have allowed the claimants to carry out that felling in the absence of consent from the relevant owners. I do not accept that submission. Although the ownership of the trees is unclear, various works have been carried out to the trees in the past 10 years, including felling a smaller tree between T2 and T3. Mr Wright said, and I accept, that there has never been an objection from anyone claiming ownership. I am satisfied that, had consent to fell been granted, there would have been no difficulty in implementing it.[79]Secondly, it was submitted that the claimants’ failure to make a further application or to appeal to the Secretary of State against the refusal of consent amounted to a failure to mitigate the damage. This was because the refusal was not based on an acceptance that it had been shown that the trees were causing damage, but which was outweighed by amenity considerations and, secondly, the claimants had recognised that the existing evidence was too weak to justify an appeal. Again, I am unable to accept that submission. Assuming in the compensating authority’s favour that the claimants were obliged to take reasonable steps to mitigate their losses, I consider that they acted reasonably in deciding to underpin rather than appeal. In reaching this conclusion I have borne in mind that the refusal was issued in September 2005, some two years after the Wrights first made their claim and that it might have taken up to 2 more years to obtain an appeal decision, whose outcome was uncertain, particularly since it would have been open to the decision-maker to conclude that the amenity value of the trees outweighed the cost of other remedial measures. OCA, the claimants’ arboricultural advisers, did not consider that the evidence was sufficiently strong to justify an appeal and it was not unreasonable for the claimants to follow that advice. As for the suggestion that the claimants could have made a further application to the authority, I accept Mr Green’s submission that that would have been an exercise in futility, given the approach taken by the authority in determining the original application. Issue 4 – Was underpinning within the contemplation of the compensating authority when it refused consent?[80]Miss Colquhoun submitted that, based on the evidence that was before the compensating authority when it decided to refuse consent, the loss incurred by the underpinning works was not reasonably foreseeable and did not flow reasonably and naturally from the refusal of consent. Mr Green submitted that, on the material before the authority, there can have been no doubt that underpinning was likely to be carried out if consent was refused. I accept Mr Green’s submission on this issue, given that in the arboricultural experts’ statement of agreed matters, Mr Jones accepted that he had assumed that the reference in the claimants’ application to possible engineering repair works was probably a reference to underpinning. Issue 5 – Would underpinning have been required even if the tree had been removed?[81]I can state my conclusions on this issue very briefly. I found Mr Champion’s evidence, to the effect that the potential heave likely to result if the tree was felled would not warrant underpinning, to be compelling. Mr Starr felt able to maintain his disagreement with Mr Chapman on this issue, despite his recognition that Mr Champion’s experience was very much greater than his own, and despite the fact that his only visit to the property had been four years before the damage occurred. He accepted that Mr Champion had calculated the likely amount of heave using recognised methods for doing so. The only area of disagreement concerned the use of an average water shrinkage factor of 4. Mr Starr asserted that it was not appropriate to use an average when dealing with a high volume change soil. But he did not say what other factor should be used, nor did he identify any other guidance or technical study that might assist. I find that underpinning would not have been required if permission had been granted to remove the oak trees. Issue 6 – Is compensation payable for distress and inconvenience?[82]Mr Wright said that he and his wife had suffered inconvenience and stress from living in a damaged house, such damage arising whilst permission to remove the oak trees was sought. This evidence was not challenged. The compensating authority was aware that the application for consent was made to avoid “expensive and disruptive engineering works” and must have been aware of the potential for distress and inconvenience arising from the refusal of consent. Miss Colquhoun did not suggest that this head of claim was not allowable in principle. In the light of the observations of Russell and Slade LLJ in Bell v Canterbury City Council (paras. 69 and 70 above) I consider that she was right not to do so. In my judgment the sum claimed, £750, is not unreasonable and I find that it is payable in addition to the agreed cost of underpinning.[83]The compensation payable to the claimants by the compensating authority is £24,001.25. A letter concerning costs accompanies this decision, which will become final when the question of costs is determined. Dated 22 August 2011 N J Rose FRICS

Cited in 1 later judgment