Japanese knotweed is responsible for shaving £11.8billion off the value of Britain’s property market, new research by a removal specialist claims.

As high as 4 Percent of British households are affected by this invasive plant, either directly on their property or on another property.

This invasive plant can make it more difficult to sell homes, as buyers will struggle to obtain a mortgage for a home where it’s found.

But, the largest mortgage lenders in Britain told us it is possible to obtain a mortgage on a property affected by knotweed. However, conditions might be required.

Japanese knotweed is an invasive plant that makes a property significantly more difficult to sell as buyers

Japanese knotweed, an invasive species that can make it more difficult for buyers to buy a property, is causing the sale of properties to be significantly harder.

The average value of a home that has Japanese knotweed in it is reduced by 5%, according to Environet.

It used that to estimate that with 890,000 households across the county are being hit by a typical reduction of value of £13,200 due to knotweed, this equated to £11.8billion in total.

The plant can be stopped from spreading – although this process can be costly, at around £2,500 for a 10sq m area for a herbicide treatment or £5,000 for a 10 sq m for an excavation.

Environet asserts that the best way to eradicate Japanese knotweed is from the soil. This will result in minimal regrowth.

According to the report, even though herbicide treatments are more affordable than other methods of controlling pests, they still have to be used. 

It’s because although above-ground vegetation can vanish, the root system below the ground can often be inducted into dormancy. In this way it’s more likely to re-grow in the future. 

Environet says removing the root system from the ground is the only way to deal with Japanese knotweed decisively with minimal change of regrowth

Environet suggests that Japanese knotweed can be dealt with by removing its root system. This will ensure that there is minimal regrowth.

Nic Seal of Environet said that while property sellers and buyers are required to disclose whether the property has been damaged by Japanese knotweed. However, if an infestation is professionally removed with an insurance-backed guarantee for mortgage lenders to cover the cost, the property can be restored to its original value.

He stated that herbicide treatment of knotweed was always very popular because it is cheaper, however the message is getting across that this method can only be used as a control and not a solution.

Buyers are more cautious buying property with knotweed under the ground because it’s impossible to determine if it’s dead. The environmental impact of using chemicals is also growing in concern.

Environet stated that excavation can be done during winter, which allows for the full enjoyment of summer gardens.

Mortgage lenders talk about knotweed 

SPF Private Clients, a mortgage broker, stated that Japanese knotweed might not present a problem for those who are looking to buy a home. This is in contrast to the past when it may have been a concern.

Mark Harris of SPF Private Clients said that if Japanese knotweed is identified, there will be four classifications to determine its severity. 1 would indicate the best case scenario, while 4 indicates the worst. 

According to the location of the property, the lender may accept the application.

Lenders may adjust the amount that they will lend depending on how severe the problem is. 

Although it can be difficult to secure a mortgage for a knotweed property, lenders have confirmed they will provide financing if there is a plan in place. 

Nationwide Building Society spokesperson said that Japanese Knotweed policy is determined by how close the plant is to the property. Before deciding whether to lend, we will request a specialist report on how the plant can be eradicated if it’s less than 7 metres from our property. 

‘If the tree is closer than seven metres, the lender will require written verification from the borrower that they are willing to submit a mortgage application. 

All cases are different and the requirements will be assessed individually. A specialist report may be required if Japanese Knotweed is identified by the valuer. This report will also include recommendations on how to repair the property. A report to eradicate the plant must include an insurance-backed warranty of five years against any re-infestation. 

A spokesperson from Halifax said: “The Japanese Knotweed isn’t a hindrance to our ability to lend.” 

“We will use the report of the surveyor and any other expert on the location, scale and consequences of any presence at or near the property to guide us.”  

What was the calculation of these figures? 

The ONS has officially estimated that there are approximately 27.8million British households.

Environet deemed flats 20% less susceptible to knotweed. 

This gives rise to 22,420,000 British homes. 

Environet and YouGov conducted a survey in 2021 that revealed that knotweed affects around 4 percent of all homes. This is because it can grow on the home or indirecty where another property is. 

According to Environet, this means that 889,600 houses are directly affected.

The average value of a property in Britain is £264,244, according to Land Registry’s figures for August. 

Environet stated that Japanese knotweed can reduce a property’s value by 5% on average. Based on anecdotal evidence, Environet estimates that Japanese knotweed reduces a property’s value by 5% after a management plan has been put in place. The 5% represents the potential buyer trying to lower an asking price due to the risk and stigma of knotweed coming back. 

The 5 per cent reduction translates into £13,212 being knocked off the average home.

As such, the total amount knocked off property values in Britain as a result of Japanese knotweed is therefore 889,600 households multiplied by £13,212, which is £11,753,395,200.

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