There are many things that can affect your property value, but you could be forgiven for thinking that the presence of a ‘weed’ would not have any significant impact. You couldn’t be more wrong if the weed in question happens to be a knotweed of the Japanese variety.

Japanese knotweed can cause significant damage to your property, hitting you in the pocket should you remain and attempt to remedy the problem, or be looking to move to a new property in which case you’ll probably still have to sort the knotweed issue before you can sell. Knotweed can also even impact on you should the invasive weed be in close proximity to you but on an adjoining property.

Read on to find out about Japanese knotweed, how to get rid of knotweed, the damage it can cause to your property, and the costs of knotweed on properties, mortgages and the UK as a whole.

What is Japanese knotweed?

Japanese knotweed was introduced to Britain by the Victorians in the 19th century as an ornamental garden plant. The Victorians weren’t aware of how invasive and hard to keep under control Japanese knotweed actually is, so for years it has gone largely unchecked.

In its traditional homelands of Japan, China and Taiwan, knotweed doesn’t cause anywhere near as much harm and damage as it does outside of its natural environment. This is because it has plenty of natural predators such as fungal pathogens and insects, but these don’t exist in Europe, meaning the weed can grow prolifically.

Classed as ‘controlled waste’ under the Environmental Protection Act 1990 knotweed is only allowed to be disposed of at licensed landfill sites. The proliferation of fly tipping in recent years has inadvertently caused the weed to spread. Some experts claim today that there is not a 6 square mile section of the UK that doesn’t contain knotweed.

How do you kill or get rid of Japanese knotweed?

Now, if you are wondering how to kill Japanese knotweed? Japanese knotweed treatment is difficult as the plant is extremely hardy, is resistant to burning, and keeps growing back. Herbicides, such as glyphosate based products, can be used in some cases, but the only way to fully and permanently get rid of Japanese knotweed is to fully excavate the often extensive network of underground roots, or rhizomes as they are known.

There are a number of other more eco-friendly alternatives for getting rid of knotweed. These include the MeshTech method which works by forcing the plant to sever its own stems on a mesh placed over it as it grows. Another herbicide-free method includes the use of biological control in the form of releasing natural predators, such as the psyllids insect, which although it will not kill Japanese knotweed, may help naturally keep it under control.

What damage can Japanese knotweed cause?

Japanese knotweed is by far and away the most feared weed for homeowners and property buyers as it can really take hold and cause significant damage. Capable of growing to around two metres in height, it is its roots that are the real problem. The roots can grow to a depth of 3 metres and stretch out more than 7 metres.

The roots can spread rapidly, and if left untreated, can block drains, weaken walls and masonry and damage the foundations of your property. The most obvious signs of knotweed damage will be that caused to above ground such as tarmac and paving where the knotweed (in some cases growing by as much as 4cm per day) can penetrate weak points and start to grow through it. Not only will you face the costs of repairing the damage, but also the substantial costs of removing the knotweed itself.

What impact on my property value can Japanese knotweed have?

If left unchecked then the impact on your property value of a knotweed invasion can be substantial.

In one case in 2011 it was reported that a Hertfordshire home, originally valued at £305,000, was later valued at £50,000, and considered impossible to sell unless the invasive Japanese knotweed was dealt with.

Additionally, you need to be aware that it is your responsibility to not allow a known knotweed invasion on your property to spread onto a neighbours land. If knotweed spreads to the neighbours land from your property then you are liable and could face a claim from the neighbour.

If selling a residential property then you are asked to complete a Seller’s Property Information Form which asks you to confirm whether knotweed is present on the property. You could face legal action if you knowingly deny the presence of Japanese knotweed on the property.

What impact does it have on mortgages?

Finding a mortgage for a property affected by knotweed can be difficult, though not impossible. Most lenders will require a professional survey in order to evaluate the damage or potential risk.

If knotweed is present on your land, then the distance of it from your dwelling is a factor. If the knotweed is on the land but more than 7 metres away from the house then a survey would help determine the associated risks of the infestation and assist with a mortgage approval.

However, if the knotweed is within 7 metres of the living space, then it is likely that the risks would be considered greater or it might be considered that the property may have sustained damaged due to the weed. Remedial work may need to be carried out before any mortgage approval would be granted.

The knotweed does not even have to be on the property you are seeking a mortgage for, as in many cases, if the knotweed is within 7 metres of the property boundary, this could be considered a risk by some lenders and impact on your chances of securing the mortgage.

What are the known costs of knotweed to the UK?

Knotweed can be costly to control and remove. It can have an impact on both domestic and business properties, some of the costs of which are highlighted below.

  • Experts estimate the cost of keeping Japanese knotweed under control could be adding 10% or more to construction and development projects in the UK.
  • A DEFRA analysis estimated a country-wide cost of £1.5 billion for knotweed control.

If you suspect that you have knotweed on your property then there is no substitute for seeking the advice of a professional who can firstly identify the presence of Japanese knotweed and then advise you on the best next steps to take. Ignoring the issue will only cause greater damage to your property and your pocket.

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