Oct 2022

Japanese Knotweed Infestation in Residential Property


A typical Japanese knotweed infestation in a residential property may result in a loss of amenity, some disruption to landscaped areas, driveways, paths and so forth. There may possibly be  damage to footings or foundations of lightweight structures, but it is rare for there to be structural damage to the foundations or walls of dwellings. Typical effects and affected areas that may be encountered are:



In many cases there is a loss of amenity. This may range from a minor inconvenience to a major loss.


Patios, paths and driveways:

Often there may be no major damage to patios, paths and driveways relating to the presence of Japanese knotweed. However, like many other plants, Japanese knotweed can sprout up between patio slabs, joints in concrete driveways and cracks in brick paving. If the plant is allowed to grow unconstrained, slabs may be lifted. Tarmac surfaces are also susceptible to damage, particularly around edges, and certainly if laid on top of Japanese knotweed.


Boundary, garden and retaining walls:

In the main, well-built boundary, garden or retaining walls should resist damage from Japanese knotweed. However, like many mature shrubs and trees, very mature stands of Japanese knotweed (with massive root ‘crowns’) can undermine or push over garden walls over a period of years.



As with many other plants, mature stands of Japanese knotweed can worsen existing damage to lightweight, insubstantial and poorly founded outbuildings such as garden sheds, greenhouses and, in very rare cases, poorly built garages.


It is not advisable to try to remove Japanese Knotweed yourself

Many types of knotweed can easily be mistaken by the untrained eye and has the potential to spread when it’s dug up

Check if you have an invasive weed for free




Although the effects may be like those described for outbuildings, owners understandably attribute greater importance to these structures. Where serious difficulties are encountered, it is usually due to a conservatory having been constructed on top of mature, untreated Japanese knotweed due to inadequate site clearance, rather than Japanese knotweed ‘invading’ the conservatory from a nearby location.


Drains and other buried services: 

Like other trees and shrubs, Japanese knotweed roots/ rhizomes can exploit existing cracks and gaps in drainage pipes in search of water, potentially causing further damage and, in some cases, blocking drains. Large, densely packed mature stands of Japanese knotweed can disrupt drain runs where allowed to grow unconstrained for many years.


Multiple affected properties: 

In some localities, large areas of mature infestation can span multiple landowner boundaries. This typically occurs where dwellings are adjacent to non-residential land or in areas where there is a preponderance of short-term lettings, for example annual student lets.





Source: RICS Japanese Knotweed and residential property doc



Source: PCA invasive weed control document library





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Japanese Knotweed
Giant Hogweed
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