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Japanese knotweed and residential property

Japanese knotweed and residential property
Executive Director - Mon Jan 09, 2012 @ 11:24AM
Comments: 0

knotweed_at_entrance_to_estuary_off_3rd_Ave..jpgThe Royal Institution of chartered surveyors published a paper to help residential practitioners consider the implications of a Japanese Knotweed intrusion on or near a dwelling, when undertaking valuations of residential property in the UK. Residents in BC also struggle with Japanese knotweed and the paper should be useful to property owners, real estate agents, mortgage brokers and surveyors who have to deal with this plant.  CONCLUSION: THIS PLANT MAY AFFECT THE VALUE OF YOUR PROPERTY AND EARLY DETECTION AND CONTROL IS THE BEST WAY TO MITIGATE DAMAGE.

Web site for full paper can be accessed: https://consultations.rics.org/consult.ti/japaneseknotweed/viewCompoundDoc?docid=1228212&sessionid=&voteid=&partId=1228212



RICS information papers

This is an information paper. Information papers are intended to provide information and explanation to RICS members on specific topics of relevance to the profession. The function of this paper is not to recommend or advise on professional procedure to be followed by members.

It is, however, relevant to professional competence to the extent that members should be up to date and have knowledge of information papers within a reasonable time of their coming into effect.

Members should note that when an allegation of professional negligence is made against a surveyor, a court or tribunal is likely to take account of any relevant information papers published by RICS in deciding whether or not the member has acted with reasonable competence.


1. Scope

1.1 This information paper (IP) aims to help residential practitioners consider the implications of a Japanese Knotweed intrusion on or near a dwelling, when undertaking valuations of residential property in the UK.



1.2 The IP includes reference to the main UK legislative and regulatory provisions that affect, or are considered likely to affect, residential value. Although these legislative and regulatory frameworks differ between England, Wales, Scotland, and Northern Ireland, the essential features governing Japanese Knotweed control and disposal are broadly similar.



1.3 This IP describes the nature of the Japanese Knotweed problem, the scale of the damage the plant can cause, and outlines the main methods of treatment. The paper puts forward an assessment methodology to help valuers objectively describe the scale of Knotweed intrusions, allowing other stakeholders to make balanced and measured decisions. In addition, Appendix C includes an illustrated 'on-site' identification chart designed to help residential practitioners recognize Japanese Knotweed at all the different seasons of the year.



1.4 This IP should be read in conjunction with the latest edition of the RICS Valuation Standards - Global and UK (the 'Red Book'). However, its scope extends beyond valuations conducted in accordance with the standards. Therefore, residential practitioners are encouraged to take note of this IP when carrying out the following professional services:

  • preparing valuations for the purposes of agency;
  • providing RICS Condition and HomeBuyer Reports;
  • Single Surveys in Scotland, and
  • building surveys.

1.5 Important note:

The Wildlife and Countryside Act 1981 originally included only giant hogweed (Heracleum mantegazzianum) and Japanese knotweed (Fallopia japonica). However, in April 2010 a further 36 plants were added onto Schedule 9. For further information on these other invasive species, please visit the website of the GB non native species at tps://secure.fera.defra.gov.uk/nonnativespecies/home/index.cfm

2. Introduction

2.1 The Japanese Knotweed problem

2.1.1 Japanese Knotweed is a hardy bamboo-like perennial plant that grows quickly and strongly. It spreads through its underground rhizomes or roots and thick clumps or stands can quickly grow to a height of over two metres. It was introduced into the UK in the mid-19th century and was initially popular with landscapers because of its ability to grow quickly and form dense screens. However, it soon became a problem because of its ability to out-compete indigenous flora and their associated fauna. In 1905 the Royal Horticultural Society was warning its readers against planting Knotweed in their gardens unless '...it is kept in check' and even the famous landscaper Gertrude Jekyll advised that it should be '...planted with caution'.

2.1.2 During the first half of the 20th Century, the spread of Japanese Knotweed beyond the original landscaped gardens was broadly known yet many nurseries still sold the plant until the early 1930s. East Cornwall was particularly badly affected where the price of a house was reputedly reduced by £100 because of the plant (Bailey JP, Connolly AP 2000).

Eventually the government took action. Japanese Knotweed was included in the Wildlife and Countryside Act 1981, making it an offence to 'plant or otherwise cause Japanese knotweed to grow in the wild'

2.1.3 In the last few years this uneasy relationship with the plant became more of a problem when some lenders reviewed their policies. A number of loans on properties affected by Japanese Knotweed were declined. Several of these cases became prominent news stories, changing the status of Knotweed from a complication that was simply 'difficult to solve' to one that could result in property sales failing.

2.1.4 However, the residential property market has faced controversial issues before. Since the mid-1970s the problems of building movement, high alumina cement, asbestos, prefabricated concrete buildings, lead, radon, and electromagnetic fields have presented assessment difficulties that have been largely resolved and assimilated into the lending process. There is no reason why the assessment of Japanese Knotweed cannot follow a similar route.

2.1.5 For the purposes of this paper, 'Japanese Knotweed' refers to all types of Japanese Knotweed defined by the Wildlife and Countryside Act 1981.


2.2 The Council of Mortgage Lenders (CML) and the Building Societies Association (BSA)

2.2.1 The members of the CML and the BSA account for the majority of UK residential mortgage lending. Both represent the views of their members, but neither can impose policies. When the Japanese Knotweed problem became apparent, the CML consulted its members. It did not publish a formal policy, but it was clear that there was a general reluctance to lend on Knotweed-affected properties. However, some individual lenders are willing to consider applications on a case-by-case basis once remediation works have been implemented. Although conditions will vary in practice, these lenders will generally want to see evidence of:

  • an initial treatment; and
  • a commitment by the owner of the property to fund, in advance, a three- or four-year treatment programme effective against Japanese Knotweed.

2.2.2 Individual lenders adopt policies that reflect their own commercial priorities. The variation in approach across the sector presents a challenge for registered valuers, especially those who carry out mortgage valuations for several different lenders.


2.3 Insurance companies

2.3.1 Discussions with the Association of British Insurers (ABI) and some insurance companies revealed the following:

  • Insurers do not generally ask any specific questions about Japanese Knotweed when a homeowner applies for a building insurance policy.
  • Although it is not specifically excluded, most buildings insurance policies do not cover damage and problems caused by Japanese Knotweed. Additionally, because the damage occurs gradually, it is unlikely to be covered in the future.
  • Where Japanese Knotweed originates from a neighbouring property, insurance companies are likely to pursue others for the costs of the damage caused.
  • A number of lenders claim that they are unable to obtain insurance cover for property affected by Japanese Knotweed.

2.3.2 This can leave a homebuyer in a difficult situation where their preferred lender will not grant a mortgage unless the homebuyer can secure a building insurance policy that covers damage caused by Japanese Knotweed; but the homebuyer cannot get an insurance policy that does.

2.3.3 Consequently, lenders and owners may need to tackle the problems posed by Knotweed without the support of building insurance policies.

3. The scale of the problem

3.1 How much of a problem does Japanese Knotweed really cause?

3.1.1 Japanese Knotweed has caused problems in the residential market because of concerns about the damaging effects of this invasive plant. However, these concerns are often based on misunderstanding and overreactions. Below, we explore the extent of the damage that can be caused.


3.2 Japanese Knotweed damage - the worst case scenario

If we define the level of damage that most commentators would consider 'serious', it can help residential practitioners be less susceptible to misinformation and so make balanced judgements. This section describes 'serious' damage and section 4.6 estimates the likely cost of this type of damage.

3.2.1 The most common effects and affected areas include the following.

  • Drains and other buried services: Knotweed roots can exploit existing cracks and gaps in the pipes in their search for water, which will further damage and, in some cases, block the drains. Large, densely packed clumps or 'stands' of Japanese Knotweed can disrupt drain runs. In the worst cases, the drains must be renewed.
  • Patios, paths and drives: Japanese Knotweed can exploit poorly laid surfacing, grow between slabs and movement joints of concrete drives and disrupt brick paving. Repairs can involve the removal of the existing paving and bedding, eradication of the plant, removal of the disruptive crowns and roots and replacement of the path, patio or drive.
  • Boundary and retaining walls: closely packed stands can undermine garden walls with shallow foundations. The mass of the stands can 'push over' retaining walls, often resulting in sudden collapse.
  • Outbuildings: vigorous stands of Japanese Knotweed can overwhelm lightweight, insubstantial and poorly founded outbuildings such as garden sheds, greenhouses and poorly built garages.
  • Conservatories: although the effects will be similar to those described for outbuildings, owners and valuers usually attribute greater importance to these structures; thus, Knotweed-affected conservatories may affect value.
  • Gardens: the invasive nature of the plant can ruin well-planned and well-stocked gardens. Some owners spend tens of thousands of pounds on renovating and redesigning outside spaces, including sophisticated water features and bespoke outbuildings. Japanese Knotweed can spoil much of this.

3.2.2 Additionally, the Environmental Protection Act 1990 contains a number of legal provisions that designate Knotweed-contaminated soil as 'controlled' waste. Only properly licensed organisations may remove this waste from a property and they must take it to appropriately licensed waste facilities. This can have serious implications for owners who want to develop their property. In properties affected by Knotweed, large amounts of contaminated soil are likely to result from activities such as:

  • adding an extension to the main building;
  • redesigning the garden; and
  • maintaining and repairing the property following a Knotweed invasion (for example, re-laying paths and drains).

The need for licensed removal of this contaminated soil and any dead plant material will obviously add to the cost of the work.

3.2.3 There are some claims that Japanese Knotweed can result in damage that is more dramatic to buildings, including damage to foundations and plants forcing their way into habitable spaces of dwellings. These extreme problems are thankfully very rare and exceptional.

4. Effective treatment of Japanese Knotweed

4.1 Introduction

4.1.1 Once it is established, getting rid of Japanese Knotweed can be challenging. As the Royal Horticultural Society states on its website: 'eradication requires steely determination'. Below we review the different treatment options and evaluate their suitability for use in the residential setting.


4.2 Excavation of the plant and its roots

4.2.1 Knotweed-infested soils can be excavated and removed to an off-site, appropriately licensed, waste-management facility.

4.2.2 The volume of excavated soils can extend to 3m vertically and 7m horizontally from the above-ground growth, resulting in large volumes of waste soil. Disposal costs range from £25 to £50 per tonne (not including landfill tax), with the result that excavation of even a relatively small Knotweed infestation can cost several thousand pounds in waste charges alone. Typically, off-site disposal can result in total treatment costs in excess of £10,000.

4.2.3 However, it is possible to reduce the volume of Knotweed-infested waste soils by segregating rhizomes and crowns (see Appendix B for definitions of these terms). There are a variety of picking, sorting and screening techniques that can achieve this.



4.3 On-site burial and/or encapsulation with membranes

4.3.1 Knotweed can be excavated and then buried on-site, but unless it can be covered with 5m or more of overburden, a specialist root barrier membrane should be installed to fully or partially encapsulate the Knotweed-bound soil, to prevent any regrowth. A root barrier membrane can also be used to encapsulate Knotweed where space does not allow burial at all.

4.3.2 One on-site burial technique is the use of vertical barriers to prevent Knotweed crossing boundaries. This is a popular approach if adjoining landowners are not co-operating with a cross-boundary programme to treat Knotweed infestation. However, vigorous Knotweed growths can often breach vertical root barrier membranes unless they are several metres deep and this should not therefore be relied upon as an effective treatment on its own.



4.4 Biological control

4.4.1 Biological control involves the introduction of a 'pest' species that will attack and control the target 'host' species (in this case, the Knotweed). It is effectively a grazing system, whereby the growth of the Knotweed is controlled to a level that keeps it in check. Biological control does not result in the death of the Knotweed, as this would be counterproductive to the pest species that feeds on it.

4.4.2 A trial is currently underway using a Japanese sap-sucking insect, which could prove an effective biological control agent for Japanese Knotweed. However, it is unlikely that this will change current legislation on the issue.



4.5 Chemical control

4.5.1 Chemical control is the application of specialised herbicides to Knotweed plants over a period of several growing seasons. This is often the cheapest treatment option costing between £3,000 and £5,000 in total for a typical three-bedroom semi-detached house. However, this method can take more than three years to be effective.

4.5.2 In a residential context where space is limited and property boundaries are closely located, planned and managed chemical control is the only realistic option for most properties in terms of practicality, cost and the need to satisfy lender requirements.



4.6 The costs of effective treatment

4.6.1 When preparing a valuation, the registered valuer must account for a variety of issues and factors. Where Knotweed affects a property, the valuer requires a measure of the magnitude of the problem. An estimate of the cost of eradication and subsequent repair can provide this.

4.6.2 Figure 1 shows a garden of a three-bedroom, semi-detached house in a suburban location in a medium-sized British city. It is assumed to be in a satisfactory condition, but has been affected by a large stand of Japanese Knotweed. This is approximately four metres from the rear wall of the house, with the red dotted line showing the extent of the above-ground growth. The stand and its growth has:

  • blocked and damaged the rear drain and inspection chamber;
  • disrupted the rear patio, leaving many uneven paving slabs;
  • damaged the concrete slab beneath the greenhouse and distorted the metal frame;
  • damaged several panels of the woven timber boundary fence; and weakened the poorly built garage to the extent that it is now beyond repair.

Figure 1


4.6.3 To simplify the scenario, we will assume the neighbour will co-operate with the treatment scheme and meet their share of any costs.

4.6.4 In addition to the price of repairing the damage, the costs of a four-year chemical-control treatment programme by a specialist contractor is assumed to be £3,000- £5,000. A further sum of £750 is required to cover legal and professional fees for initial advice on the problem.

4.6.5 Using the Building Cost Information Service (BCIS) figures published by RICS, total remediation costs are likely to be as indicated below.




Cost (£)

Drain replacement


New patio


New greenhouse


Part fence replacement


New garage


Treatment costs


Legal and professional fees



£15,413 plus VAT

4.6.6 In most situations, the case we have illustrated in Figure One is as bad as Knotweed gets in a domestic situation. Once there is a broad acknowledgement that most Japanese knotweed intrusions are less troublesome than this and can be controlled without prohibitive costs, Knotweed can be considered as just one of the many factors that have to be taken into account when preparing a valuation.

4.6.7 Important note: The above amounts do not include the removal and disposal off-site of any contaminated excavated material which would increase the costs further.



4.7 Impact on value

4.7.1 By quantifying the likely cost of treatment and any necessary repairs in this way, the impact of Japanese Knotweed can be taken into account in the valuation process and reflected in the same way as any other defect or item of disrepair.

4.7.2 Once there is an acknowledgement that the illustrated case is about as big as it gets, that Japanese Knotweed is unlikely to cause serious structural damage to buildings and that it can be controlled in a domestic context without incurring prohibitive costs, it can start to be considered as just one of the many factors to be taken into account when preparing a valuation.

4.7.3 If treatment is deemed necessary in cases where Knotweed is present in the grounds but no damage has been caused to the property itself, the sole expense may simply be the cost of the treatment. In some circumstances, this may have no adverse affect on value.

5. An assessment framework for Japanese Knotweed

5.1 Introduction

5.1.1 An assessment of the seriousness of any problem affecting a residential property is usually carried out in three stages:

  • collection of information about the nature and extent of the problem;
  • analysis of this information so that the magnitude of the issue can be established; and
  • the use of this assessment as a basis for client advice.

5.2 Collection of information

5.2.1 Information is collected through inspection. The inspection process can be subdivided into the following parts:

Knowledge of the area and pre-inspection checks

5.2.2 Local knowledge and pre-inspection checks can help the valuer identify general neighbourhood features regularly associated with the growth of Japanese Knotweed. Such pre-inspection checks may include postal-code searches for flood risk and other environmental issues, the use of mapping and 'street view' sources. Neighbourhood features associated with the growth of Knotweed typically include the presence of:

  • local water sources, such as culverts, ponds, canals and lakes;
  • public and private paths, cycle-paths, roads, railway or underground railway embankments, dual carriageways and motorways;
  • large open spaces, car parks and cleared sites; and
  • commercial and industrial buildings, workshops, storage depots and similar.

The property in its neighbourhood setting

5.2.3 All of the likely locations for Japanese Knotweed growth identified in 5.2.2 can similarly be identified prior to and after the actual inspection, for example, while driving through the neighbourhood, arriving at or leaving the property, parking, and preparing for the inspection.

The inspection of the property

5.2.4 The Red Book sets out the standard approach to the provision of valuation advice to prospective lenders in the mortgage valuation. This makes it clear that in normal circumstances, as much of the exterior of the property and the land within the ownership as is readily accessible without undue difficulty or risk to personal safety should be inspected visually. At the time of writing, the current version adds:

'Although personal judgement has to be used, this inspection should include all of the property that is visible when standing at ground level within the boundaries of the site, and adjacent public/communal areas, and when standing at the various floor levels.''


'Where there are locational factors that may impact value they should be recorded and reported. Certain problems, such as...invasive vegetation... are particularly prevalent in certain districts. If appropriate, the valuer should make some reference to these defects, even if the subject property does not appear to be affected at the time of the inspection.' *1

In most cases this visual inspection of the grounds of a property is relatively cursory and takes place naturally during the normal inspection process. However, in circumstances where there may be a greater risk of Japanese Knotweed, for example, where it is widespread locally, this part of the inspection may require particular attention.

If the client wants greater assurance, he or she should commission a more detailed inspection , such as a HomeBuyer Report or a building survey. Although these are not specialist Knotweed services, the inspection of the property and its grounds will be more comprehensive than with a mortgage valuation inspection and there will thus be a greater opportunity to identify any growth. In these cases, inspection along and over the boundaries is important especially where those features listed in 5.2.2 are present.

In Scotland, the extent of the inspection for a Single Survey is approximately the same as for the mortgage valuation described above.

*1 These statements may be revised in subsequent versions of the Red Book. Registered Valuers have a professional duty to use the current version.

5.3 Identification of Japanese Knotweed

5.3.1 Many authoritative publications on Japanese Knotweed have been in the public domain for a number of years; however, not all residential practitioners are confident in their ability to identify the plant.

5.3.2 To help address this problem, this information paper includes an easy-to-use identification guide for valuers, illustrated in Appendix C. Intended to be taken along on inspections, this A4-size, chronologically structured chart is divided into three sections to aid identification throughout the year.

The growing season (March-October):

  • March-April: at this time of year the plant will be at an early stage of its annual life cycle, and some of the classic visual characteristics will not yet have developed. Despite this, its appearance can still be distinctive. It is described and pictured at Appendix C of this IP.
  • May-October: during these months the growth of Knotweed will be most vigorous, and in normal circumstances the plant should be easily identifiable. This section of the Figure highlights just four characteristics:
  • the leaf;
  • the zigzag leaf stems or 'petioles';
  • the main stems; and
  • the flowers.

The winter (October-February):

  • In these months the plant will shed its leaves and die back. Because the stems are robust, it is possible to identify Knotweed even during this season.

However, as residential practitioners are not specialists in this area, and the mortgage valuation is tightly prescribed, there is a limit to the practitioner's identification capabilities. The following scenarios indicate some of the difficulties that may be encountered:

  • Concealment: Japanese Knotweed can often be hidden amongst other dense foliage or - and this is more likely - owners may deliberately conceal growth. Typical examples include the physical removal of the plant prior to the inspection; covering over with turf and mowing the lawns before inspection; covering the garden with landscape fabric and ornamental gravel or bark chippings; and so on.
  • Mis-identification: other vigorous growing shrubs and trees can be mistaken for Knotweed. Specialist contractors report increasing numbers of abortive visits because of 'mistaken identity'.
  • Effects of treatment: during a formal treatment programme, Knotweed regrowth can be so deformed and sparse that it may not be noticed.

5.4 Building an assessment framework

5.4.1 Although the focus of this information paper is on the mortgage valuation, approximately 20% of purchasers commission their own survey, such as the RICS Condition and HomeBuyer Reports and the building survey. These include a more extensive inspection and broader advice about the condition of the property.

5.4.2 Consequently, it is logical to establish an assessment framework that supports the decision-making process across the range of inspection and survey products. Once established, this framework can be flexibly utilised by stakeholders to suit their own business objectives.



5.5 The risk assessment of Japanese Knotweed

5.5.1 This risk assessment takes into account the real risk to a property and addresses some of the concerns of the lenders and insurance companies. A number of definitions may be helpful.

  • The term 'habitable space' refers to those parts of the subject property associated with daily living not ancillary spaces (such as outbuildings and/or garages).
  • The term 'serious damage' refers to a level of damage described in 3.21 and costed in 4.6;
  • According to the Environmental Agency's 'The Knotweed Code of Practice', Japanese Knotweed rhizomes can extend up to 7 metres from the last sign of visible growth. This has been used as the minimum distance in the assessment process.



5.5.2 Where the Knotweed intrusion falls into categories 4 and 5, further investigations are required. For categories 2 and 3, the decision as to whether further investigations are needed will be based on a combination of the valuer's professional judgement and the client's particular requirements.



5.6 Properties previously affected by Japanese Knotweed

5.6.1 Although valuers may not see Japanese Knotweed during their inspections, they may be aware that the property has been previously affected. This information may result from their knowledge of the area or as a response to a 'seller's questionnaire'.

Please note: because the standard of previous treatment regimes adopted by property owners and their agents have been inconsistent, the effectiveness of older treatment programmes must be cautiously assessed.

5.6.2 Whatever the source of the information, one of two responses may be appropriate:

  • where there is NO satisfactory evidence to show that Japanese Knotweed is currently undergoing a properly planned programme or that the planned programme has been properly completed, further investigations WILL be required; or
  • where there IS satisfactory evidence to show that Japanese Knotweed is currently undergoing a properly planned programme or that a planned programme has been properly completed, further investigations will NOT be required.

5.6.3 An important feature of this process will be the definition of what constitutes 'satisfactory evidence' and although this will be a matter for the individual residential practitioner's professional judgement, it should closely resemble the 'Management Plan' described in 5.7 below.

5.7 Management plan

5.7.1 Once Japanese Knotweed has been identified, and a specialist consultant or contractor has further investigated the problem and provided a report, a Japanese Knotweed management plan should be established. This management plan can provide the necessary reassurance to both lenders and buyers that a Knotweed problem is being properly managed.

5.7.2 Although the methods of tackling Japanese Knotweed will depend on the commercial choices and preferences of the contractor, the management plan should be based on that included in the Code of Practice published by the Environment Agency and should thus be consistent across the industry. As a minimum, a management plan should include the following features:

  • A description of the property with an accurate record of the Knotweed intrusion. A scaled plan with dimensions and supporting photographs would be particularly useful.
  • The full details of the contracting organisation and a description of the methods to be used to eradicate Knotweed.
  • A treatment schedule that is updated as treatments are carried out.
  • A completion certificate that confirms the treatment is complete and that the property is Knotweed-free on the completion date.

5.7.3 Valuers should take account of this range of information when deciding whether the evidence of previous treatment regimes is adequate.

5.7.4 To meet lender requirements, other features could provide additional reassurance, as detailed below.

  • The current owner must pay all costs associated with the management plan 'up-front', so that the treatment programme can be completed without relying on financial support from subsequent owners.
  • The management plan should be transferable to any subsequent owners.
  • The management plan should cover the whole of the property and not just those affected parts identified by the original valuer.
  • An insurance-backed guarantee for the management plan should ideally be obtained, to reassure lenders, insurance companies and buyers further. Such a guarantee should ensure that in the case of insolvency of the original treatment company, another suitable company will complete the treatment programme.

5.7.5 Important note: It is impractical to guarantee that Japanese Knotweed will not return following the completion of a treatment programme. Consequently, the mandatory insurance should be restricted to ensuring that the treatment is completed.


5.8 Contractors and consultants

5.8.1 As standards develop across the treatment industry, it is likely that lenders will begin to specify that the management plan provider is an accredited member of a recognised trade association. At the time of writing a suitably constituted trade association is not yet in existence, although related discussions are taking place within the treatment industry.

5.8.2 Until a suitable trade association is established, a Japanese Knotweed contractor or consultant appointed to carry out an effective treatment programme should be able to show they have many of the following attributes:

  • a transparent fee structure that allows the total cost of the treatment programme to be understood and agreed before any works take place;
  • a contract for the works accompanied by a warranty that the treatment programme will be completed. This should be for a suitable period of not less than six years from the start of the works;
  • a bond for the warrantee to provide protection if the warranter ceases trading during the warranty period;
  • a commitment to regular monitoring for and treatment of regrowth of Knotweed (this would usually be for at least three years, although a longer period might be necessary);
  • appropriate legal compliance for the works, including:
  • certification from the National Proficiency Tests Council (NPTC) for the application of herbicides;
  • licences for waste-handling and treatment (such as a duty of care licence, a waste carrier licence, a waste broker license and an environmental permit, including mobile plant licences for large items of treatment plant);
  • possible additional approval from the Environment Agency for the following:
  • herbicide spraying close to a watercourse;
  • excavating close to a watercourse; and
  • burial of Knotweed material on site;
  • an appropriate consideration, risk assessment and action plan for the treatment of Knotweed on adjacent properties where it could affect the warranted property;
  • proof of the following, annual insurances:
  • professional indemnity cover of not less than £2m;
  • employers' liability cover of not less than £10m; and
  • public liability cover of not less than £5m;
  • preferably current accreditations from the United Kingdom Accreditation Service (UKAS) for the following standards:
  • OHSAS 18001 Occupational Health and Safety;
  • ISO 9001: 2008 Quality Management Systems - Requirements; and
  • ISO 14001 Environmental Management System.


5.9 Neighbouring properties

5.9.1 Where the Japanese Knotweed is confined to the grounds of a single property, its eradication will normally be a straightforward process involving only two parties: the property owner and the contractor. However, where Knotweed straddles the boundaries of a number of different properties, the solution will not be so simple. Although the owner of the subject property may have paid for a treatment programme, if the owners of the neighbouring properties do not co-operate, the treatment is unlikely to be effective. In some residential areas property ownership can be complex and transient and establishing a joint strategy in this situation will be challenging. In these cases, providing root barriers along the boundary may appear an attractive option to lenders who require a straightforward, time-limited solution. However, this approach will be unsuitable for many properties for two reasons:

  • The disruption of excavations to depths of three metres will be expensive, disruptive and legally challenging, as the owner's legal advisers take into account matters relating to boundaries, party walls and general property rights.
  • Not all commentators agree that root barriers are effective ways of preventing the spread of Knotweed (see 4.3.2 for further discussion).

5.9.2 Consequently, where Knotweed is present on a neighbouring property or land, two strategies can be adopted:

  • Where the Knotweed is on both the subject and neighbouring property, the management plan should include:
  • provision for the treatment of the entire outbreak, regardless of boundary positions; and
  • a project management service in which the contractor will co-ordinate plans with willing neighbouring owners regarding access for the inspection and treatment regimes.
  • Where a neighbouring owner does not co-operate and prevents the completion of the treatment programme, the new owner of the subject property may have to commit to a continued treatment programme that will restrict the growth of Knotweed on the subject property until a cross-boundary, co-ordinated treatment programme can be agreed.
  • Conversely, where the neighbouring owner is the lead party in the management plan, the residential practitioner will want to remind the client that they should cooperate and failure to do so may expose them to legal action for negligence

5.9.3 To protect the legal interests of the subject property owner, his or her legal advisers may wish to put adjacent owners on notice of the problem, indicating what should be done to tackle the Knotweed and the possible consequences of failing to take appropriate action.


6. Conclusion

6.1 The presence and effects of Japanese Knotweed are just one of the many considerations that may affect value and just one of the variety of factors that valuers must take into account when assessing Market Value. While this invasive, non-native plant can be difficult to control, it should be recognised that timely and persistent treatment programmes can minimise its impact. As the treatment industry develops and matures, it is hoped that valuers will be able to provide more informed advice to their clients. As lenders adopt more consistent and balanced policies Japanese Knotweed should soon become just one more consideration in the complex valuation process.


Appendix A: Further sources of information

Further information on Japanese Knotweed and related issues can be found on the following websites:

The Environment Agency (www.environment-agency.gov.uk )

The Cornwall Knotweed Forum ( www.cornwall.gov.uk)

Devon County Council (www.devon.gov.uk)

GB non-native species secretariat (https://secure.fera.defra.gov.uk/nonnativespecies)

Scottish Environmental Protection Agency (www.sepa.org.uk)

Appendix B: Glossary

Included in this glossary are both terms referred to in the information paper and other commonly used terms that the valuer may encounter when undertaking desk research or investigations to support residential valuations.





Tall, hollow, bamboo-like stems


The visible part of the rhizome from which canes grow. Crowns can produce many new canes and, because of their size, can be resistant to burning or drying out.

Environmental Protection Act 1990

Part II of the EPA 1990 contains a number of legal provisions concerning 'controlled waste'. Any soil or plant material contaminated with Japanese knotweed that a person discards, intends to discard or is required to discard is likely to be classified as controlled waste. The most relevant provisions are in sections 33 and 34 of the Act.

Japanese Knotweed

The common type of Japanese Knotweed is known as Fallopia japonica, but there is a smaller compact variety called Fallopia japonica var. compacta, which reaches a height of 1 metre. Giant Knotweed (Fallopia sachalinensis), can grow up to 5 metres and a hybrid between Japanese Knotweed and Giant Knotweed, Fallopia x bohemica, is also found in the UK.


The stalk or stem that connects the leaf to the plant

Registered valuer

This is a chartered surveyor and member of the RICS who is registered with the RICS to carry out the valuation of land and property.

Residential practitioner

In the context of this information paper, 'residential practitioner' refers to a broad range of professionals involved with advising their clients about all types of residential property.


Underground stem which enables Japanese Knotweed to survive over winter, when the canes die back. Small sections of rhizome, as little as 0.7g, can regrow into a new plant.


Large clumps of densely packed Knotweed stems.

Waste Management Licensing Regulations 1994

The WMLR 1994 describe 'waste relevant objectives' in paragraph 4 of Schedule 4. These objectives require that waste is recovered or disposed of 'without endangering human health and without using processes or methods which could harm the environment and in particular without risk to water, air, soil, plants or animals; or causing nuisance through noise or odours; or adversely affecting the countryside or places of special interest.'

Wildlife and Countryside Act 1981

Section 14(2) of this Act states that 'if any person plants or otherwise causes to grow in the wild any plant which is included in Part II of Schedule 9, he shall be guilty of an offence.' Japanese Knotweed is one of the plants listed in the Schedule.




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