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What does Japanese knotweed do to a house?

Published on by Dr Paul Beckett

Japanese knotwed damage

It’s often quoted that Japanese knotweed causes damage to housing and there have been some alarming stories in the press that seem to reinforce this. However, the reality is that while knotweed is a problem you definitely do not want to have, it rarely causes the significant physical damage to built structures that is often attributed to it. So, if it’s unlikely to knock down or damage your home, why is it still considered such a property risk? In this blog post we explore the question: what does Japanese knotweed do to a house?

Physical Damage

Certain plants that are capable of causing structural damage to buildings do this by growing between small gaps and exerting sideways pressure on the built elements, prising them apart as the roots expand and grow. Loose areas of paving, stone, tarmac and joints between concrete slabs are particularly prone to damage.

Most woody species like trees cause structural damage that is similar to, or worse than, that caused by knotweed if the plants are not controlled. And herein lies the problem; as knotweed can grow so fast (sometimes up to 10cm per day), it can quickly get out of control, which can in turn lead to damage of vulnerable structures.

Building foundations and walls tend to be more solidly constructed with fewer cracks or gaps. Damage from knotweed that affects the structural integrity of buildings is therefore quite rare, and when it does happen the affected properties are usually already dilapidated or significantly neglected. As ancillary buildings like outhouses, sheds and greenhouses are often less sturdy and less well maintained, they can be affected more significantly by knotweed growing around and/or through them.


As knotweed did not evolve in balance with its ecosystem in the UK (which, incidentally, is why it is a problem here and why it’s not a problem in its native Japan), there are almost no animals or plants associated with it. This means nothing eats it, or lives on it or within it. It also grows into thick stands of bamboo-like stems that are so dense that they prevent anything growing underneath them. If you have a lot of knotweed, you therefore probably have a lot of not much else.


The financial implications have become by far the greatest impact of knotweed. The reluctance of some lenders to provide mortgage finance on knotweed affected property, and the blighting affect that causes prospective buyers’ purchasing decisions to be swayed, can have significant financial implications (read this article on the potential cost implications caused by knotweed).


With the risks of such costs come the inevitable litigation to recover damages when house sales fall through and property value is diminished by the presence of knotweed. Although the vast majority of such cases settle out of court, those that go all the way to a judgement have made the headlines (e.g. this landmark case against Network Rail).

So although the law of tort is the more significant legal mechanism with regard to knotweed, criminal prosecutions are possible too, although much rarer. Allowing knotweed to spread into the wild is a crime under the Wildlife and Countryside Act (as amended) and you could have a Community Protection Notice served on you if you allow your knotweed to sufficiently affect your neighbours (learn about Japanese Knotweed legislation here).

Knotweed Removal and Treatment

So although the physical harm and damage that can be caused by knotweed is relatively rare, particularly on well-maintained properties, the financial and legal risks can be significant.

Property risks from knotweed cannot therefore be ignored. If you are concerned that you might have knotweed on your property or be affected by it on adjacent property, then you must do something about it. Failure to get the problem assessed and treated in a manner that will mitigate the risks could result in hefty damage costs (as this surveyor recently found) or other legal action (as this Bristol firm found).

Whatever your concerns or clear requirements are, if you are worried about the potential impact of knotweed on your home or other property and would like guidance on identifying Japanese knotweed or advice on Japanese knotweed removal, please contact us for a chat. We’d be very happy to help.

About the author: Dr Paul Beckett

Dr Paul Beckett - picture

Dr Paul Beckett is one of the UK’s leading experts in Japanese knotweed and is a member of the Expert Witness Institute. He regularly provides Japanese knotweed expert witness services. He helped produce the RICS knotweed guidance for surveyors and was integral in the formation of the Property Care Association (PCA) Invasive Weed Control Group (IWCG).

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