Japanese Knotweed Flashcards
Japanese Knotweed Guidance Note
Provides information for property professionals in dealing with issues related to japanese knotweed, which is an invasive plant that can cause significant damage to properties.
What is Japanese knotweed?
HIghly invasive plant that can cause significant structural damage. Hollow stems, heart shaped leaves and small white flowers.
Impact on property
Knotweed can cause dmage to foundations, driveways, can affect property value and mortgage approvals
Legal obligation
Property owners have a duty to manage knotweed effectively. Failure to control its spread can lead to legal liabilities and potential penalties
What is Japanese Knotweed?
It is a fast growing invasive weed that can cause damage to structure. Can grow up to depths of 2 metres and extend up to 7 metres horizontally. It can grow under footpaths, buildings.
Problems caused by knotweed
If left uncontrolled can cause damage to lightweight structures e.g. freestandign walls, paths, drains. It is not typically associated with subsidence or heave.
The treatment of knotweed is expensive. Ground affected by knotweed cannot be developed without taking certain precautions such as removal and disposal of contaminated soil by licenced operators.
Typical infestations of knotweed
Gardens - loss of amenity
Paths, driveways, patios
Boundary, garden and retaining walls
Outbuildings
Conservatories - if it has been built over untreated knotweed due to inadequate site clearance.
Drains and buried services - can exploit existing cracks and gaps in drainage pipes
Environmental Protection Act 1990
Contains legal provisions that designate japanese knotweed contaminated soil as controlled waste. Only licenced organisations can remove the waste and must take it to an appropriate facility.
Surveys for pre-purchase
If an RICS member has the skill, knowledge and training to include the additional service of identifying and advising on Japanese knotweed as part of a pre-purchase survey, they can offer that, providing it is covered in their terms and conditions of engagement and it is
discussed and agreed with the client.
For most RICS members however, if a client specifically requires advice on whether or
not Japanese knotweed is present at a property, or advice on remediation, they should recommend the client commissions an inspection or advice from a specialist remediation company that is a member of a recognised trade body.
Knowledge of area and pre-inspection checks
Do pre-inspection research about the general environment, neighbourhood, subject property.
online distribution map may give rough indication of frequency of japanese knotweed.
Identification of japanese knotweed.
There is now a wealth of
information available to assist learning and there is an expectation, not least by the courts, that residential valuers and surveyors should have a working knowledge of what Japanese knotweed commonly looks like during all seasons of the year.
Documentation published by the property care association, japanense knotweed advice for professional valuers.
Site records
proximity to built structures
location, height
evidence of current or previous management
photographs
very small = 1m2 or less
small = 1m2 to 4m2 area
Assessment framework
You do not legally have to remove Japanese knotweed from your land unless it’s causing a nuisance.
The RICS state that “The new assessment process enables the valuer or surveyor to carry out a structured assessment that leads to an objective categorisation of any given infestation. The assessment utilises a decision tree and the accompanying notes form an integral part of the assessment process. The notes clarify and define the terms used in the decision tree, assisting the valuer, surveyor or other user to place the property being inspected in the appropriate Management Category”.
Management category assessment
Category A - Significant i Seek advice.mpact and action required.
Category B - Potentially significant impact,l action required. Seek advice from remediation specialist.
Category C - Low impact, Manage. No action required for mortage retention or lending purposes.
Category D - Limited impact.
Notes when assessing japanese knotweed.
Is it on site or off site.
is it actually causing visible material damage to a structure.
is it likely to prevent use or restrict access to amenity space.
Reporting to lenders
When Japanese knotweed is identified, the Management Category assessment decision tree (see section 4.5) should be used to categorise the infestation at the relevant Management Category, which can then be reported to the lender in the usual way
Management of knotweed
When it has been identified further investigation should be carried out by an accredited member. Report should be provided depending on the findings.
Remediation options
Chemical control using herbicidies
physical removal by excavation
treatment will be dependant on circumstances on site
Implications in a property valuation
Five factors are listed in a 2017 paper titled Assessing diminution in value of residential
properties affected by Japanese knotweed. The world of Japanese knotweed has moved on since 2017 but the principles outlined in the paper are still relevant. The five factors are:
* impact in the market prior to remediation
* restrictions on use of the property
* impact during remediation
* impact of infestation present on adjoining land
* post-remediation impact on future saleability.
Typical scenarios of japanense knotweed
A typical Japanese knotweed infestation in a residential property may result in a loss of amenity, some disruption to landscaped areas, driveways, paths, etc. and possibly damage to footings or foundations of lightweight structures, but it is very rare for there to be structural damage to the foundations or walls of dwellings. Typical effects and affected areas that may
be encountered are:
Will Japanese knotweed grow through new builds?
Japanese knotweed has been known to grow through new builds, however, this usually only occurs in circumstances where an infestation is particularly large
Treatment of japanense knotweed before development of new land
necessary to remove Japanese knotweed from any land affected by Japanese Knotweed that is going to be used for building. In severe cases, it might be necessary to remove the weed before construction can begin. Because of their tenacious growth patterns and seasonal growth spurts, entire plants may need to be removed to prevent interfering with your foundations or causing any structural weaknesses.
Legislation on japanese knotweed
I learned that invasive weeds are on
schedule 9 of the Wildlife and
Countryside Act 1981. Japanese
Knotweed is regarded as controlled
waste as part of the Environmental
Protection Act 1990. Japanese
Knotweed spreads through
fragments of freshly cut stems and
underground stems.
