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Japanese Knotweed: A pragmatic approach

Japanese knotweed was first introduced to the UK from Japan in 1825 as an ornamental plant and it is easy to see why, it is not unattractive. However, nearly two centuries on and despite a number of initiatives and restrictions being in place to prevent the spread of the plant, its presence is still causing major headaches for property owners and purchasers.

The problem

The plant is highly invasive and extremely difficult to control. A hidden underground mass of roots enable it to thrive even when all parts above ground are removed. It can cover a large area to the exclusion of all other species and has been known to grow through foundations and even house floors. A recent case highlighted by the national media reported how a couple saw their new build four-bedroom house reduce in value from £300,000 to approximately £50,000 overnight following the discovery of Japanese Knotweed growing extensively underground on the site. This only serves to emphasise the potential risk for homeowners, prospective purchasers and mortgage lenders alike.

As a result, mortgage lenders often take a cautious stance with regards to lending money when Japanese Knotweed has been identified.

The solution

Although it may not always seem a blessing to the vendor when it crops up in a survey, early identification of the problem is essential. Any comprehensive survey report will contain a small section which confirms that the appropriate checks have been carried out. If signs of the weed are established, the following steps should be followed:

  1. Understand the extent of the problem – There are a range of companies that are able to provide bespoke reports on the issue. As the majority of the growth will be taking place up to three metres underground this is specialist work, therefore evidence of their track record and references should be sought.
  2. Evaluate the options available – These include the use of correct herbicides, controlled burning, burial of geotextile matting, and removal of contaminated soil. Your specialist will be able to advise you on the appropriate course of action.
  3. Understand your responsibilities – Appointing an experienced and reputable contractor to undertake any associated work is a must. It is an offence under the Wildlife and Countryside Act 1981 to cause the growth of the plant in the wild; and disposal must be done in accordance with the Environmental Protection (Duty of Care) Regulations 1991. It should also be noted that once you are aware of the presence of Japanese Knotweed, there is a risk in doing nothing. There have been instances of civil action being taken against Landowners who allow the weed to spread into neighbouring land.
  4. Execute a control or eradication plan – Considering the responsibilities set out above, the use of a credible and specialist contractor is essential. Prior to undertaking the work, it is worthwhile checking with a lender that your chosen course of action along with a guarantee from the contractor will suffice in enabling them to proceed with the mortgage agreement.

If you are purchasing or selling a property

Evidence of Japanese Knotweed does not necessarily need to signal the end of a property transaction. However if it is identified in a survey, only demonstrating to the mortgage lender that there is minimal risk of the weed causing damage to the structure of the house in the future, will move the transaction forward. This can be undertaken by the vendor, purchaser, or both.

If you own or manage properties

Whether you own or a manage property, protecting the value of the asset will be high on your list of priorities. With this in mind, if Japanese Knotweed is located, immediate action is necessary to ensure potential damage is minimised in order to avoid jeopardising any future sale.

In summary

Whether you’re purchasing, selling, or you own or manage a property that has Japanese Knotweed, the best possible way of managing and dealing with this problem will be through a sensible and pragmatic approach to understand the extent of the problem; and if necessary, appoint the appropriate experts to control or eliminate the risk.

Finnegan Property Services are independent Chartered Building Surveyors who undertake condition, purchaser, and vendor surveys. We offer advice on the management, control, and eradication of Japanese Knotweed. If you would like to discuss any of the issues covered in this blog contact or call 020 3137 8078.


Posted on 2 October, 2015

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