Japanese Knotweed

Question 1

Japanese Knotweed Guidance Note

Answer 1

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.

Question 2

What is Japanese knotweed?

Answer 2

HIghly invasive plant that can cause significant structural damage. Hollow stems, heart shaped leaves and small white flowers.

Question 3

Impact on property

Answer 3

Knotweed can cause dmage to foundations, driveways, can affect property value and mortgage approvals

Question 4

Legal obligation

Answer 4

Property owners have a duty to manage knotweed effectively. Failure to control its spread can lead to legal liabilities and potential penalties

Question 5

What is Japanese Knotweed?

Answer 5

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.

Question 6

Problems caused by knotweed

Answer 6

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.

Question 7

Typical infestations of knotweed

Answer 7

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

Question 8

Environmental Protection Act 1990

Answer 8

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.

Question 9

Surveys for pre-purchase

Answer 9

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.

Question 10

Knowledge of area and pre-inspection checks

Answer 10

Do pre-inspection research about the general environment, neighbourhood, subject property.
online distribution map may give rough indication of frequency of japanese knotweed.

Question 11

Identification of japanese knotweed.

Answer 11

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.

Question 12

Site records

Answer 12

proximity to built structures
location, height
evidence of current or previous management
photographs
very small = 1m2 or less
small = 1m2 to 4m2 area

Question 13

Assessment framework

Answer 13

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”.

Question 14

Management category assessment

Answer 14

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.

Question 15

Notes when assessing japanese knotweed.

Answer 15

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.

Question 16

Reporting to lenders

Answer 16

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

Question 17

Management of knotweed

Answer 17

When it has been identified further investigation should be carried out by an accredited member. Report should be provided depending on the findings.

Question 18

Remediation options

Answer 18

Chemical control using herbicidies
physical removal by excavation
treatment will be dependant on circumstances on site

Question 19

Implications in a property valuation

Answer 19

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.

Question 20

Typical scenarios of japanense knotweed

Answer 20

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:

Question 21

Will Japanese knotweed grow through new builds?

Answer 21

Japanese knotweed has been known to grow through new builds, however, this usually only occurs in circumstances where an infestation is particularly large

Question 22

Treatment of japanense knotweed before development of new land

Answer 22

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.

Question 23

Legislation on japanese knotweed

Answer 23

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.