Japanese Knotweed Damage

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Japanese knotweed damage can often occur when the invasive plant attempts to grow through the weakest points of a property’s foundation & out-structures. If you suspect Japanese knotweed may be growing on or near your property, our surveyors are highly trained in all matters relating to Japanese knotweed identification, inspection and control. We have the skills required to identify and control problematic JK growing on or near your property.

How deep are Japanese knotweed roots?

The Environment Agency revealed that Japanese knotweed rhizomes can extend 7 meters horizontally and 3 meters vertically from the visible ‘above-ground’ growth.

Even if Japanese knotweed sprouts on land that is close to your property, its underground rhizomes could have already spread under your house. Once the invasive roots spread under your home, it starts to exploit vulnerable areas to sprout & invade.

**Read this article: Can You Build On Land With Japanese Knotweed? for further information about land owners responsibilities.** 

Japanese knotweed has the potential to grow as much as 10 centimetres per day in the summer, giving it the ability to spread quickly and take over properties at a rapid rate. Deep digging can often be required to eradicate it from a property entirely. Removing the infestation whilst it still has a shallow root structure is the best case scenario.

What damage can Japanese Knotweed Cause?

Japanese knotweed, an ornamental plant when it first arrived in Europe in the nineteenth century, is considered a damaging and destructive plant. It can destabilise and weaken property foundations, piping & water supplies, fences, boundaries, outbuildings and even flood defences through its rhizome system. It’s even known to cause sudden collapsing & destruction to older properties and structures. Certainly, no longer to be left the ‘ornamental plant’ it used to be.

Typical damage from Knotweed includes:

  • Tarmac, Paving & Patios – Japanese knotweed can grow between hard surfaces, like paving slabs, bricks, block paving’s, and even force its way through tarmac.

  • Water Supply & Drainage Pipes – Japanese knotweed roots can find their way into underground pipes in search of water, which can further damage and clog your drainage system. Large, densely packed knotweed roots and rhizomes can cause disruption in drain runs & water pipes alike. In the worst cases, these pipes have to be replaced completely.


  • Building Foundations – Japanese knotweed can penetrate, or at the very least, weaken significantly, just about any hard surface you place it up against. Including your properties foundations.

  • Retaining Wall Structures – Japanese knotweed can undermine garden walls by attacking their shallow foundations and old or poorly constructed fences. Its dense masses can cause retaining walls & fence supports to ‘push over’ with sudden collapse.

  • Reduction in Property Values – Japanese knotweed is an unacceptable risk to lenders, who will often refuse mortgages if Knotweed is identified on a property and there is no management or treatment plan in place. Cash buyers would value the property about 20 % lower than the asking price.

Why does Japanese Knotweed cause so much damage?

The biggest reason Japanese knotweed causes so much damage is due to ignorance or wilful negligence. All knotweed infestations start small. Whether the infestation starts due to a fragment of rhizome, or is the result of a neighbouring patch of land. There is always time to prevent Knotweed from doing any severe damage.

The longer any potential Japanese knotweed infestation is left unchecked, the more opportunity it has to spread, grow stronger and threaten your property with severe damage. Even a small infestation of Japanese knotweed on your property can have a significant impact on the value of your home and your ability to sell it at a later date.

How do I prevent damage & limit removal costs?

If you suspect an infestation of Japanese knotweed on your property or that of a neighbour, be sure to contact our team of trained surveyors for further identification. DO NOT ignore it.

When Japanese knotweed has been identified on your property or a neighbouring property, you should notify your immediate neighbours about it immediately so that they can remain vigilant. Depending on which property the infestation resides on, the homeowner then holds the responsibility of removal of the infestation. Catching it as early as possible in its smallest physical form is the most cost-effective method of removal, before more severe damage & repair costs follow.


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