What you need to know about Japanese knotweed if you’re buying or selling property

The mere mention of “Japanese knotweed” has been known to send many a property seller into a cold sweat.

Regardless of how the market is performing, a nightmare such as knotweed is likely to cause some sleepless nights, as it has been known to have a negative impact on the value of your bricks and mortar.

According to property firm Moverly it’s one of the biggest homebuyer turn-offs, and could potentially result in your house price dropping by up to 15pc.

The dreaded weed has also gained a reputation for scuppering borrowers’ chances of getting a mortgage.

But even though there are lots of horror stories out there, experts say knotweed can, in most cases, be dealt with.

Nic Seal, of invasive plant specialist Environet, said: “Homebuyers are increasingly taking a pragmatic approach. As long as the infestation is professionally treated with an insurance-backed guarantee, affected properties can now be bought and sold.”

Here, Telegraph Money takes a closer look at why knotweed has been branded such an issue, and what buyers and sellers need to know if it springs up on a property.

Why is Japanese knotweed so bad?

According to Environet, Japanese knotweed currently affects around 1.4 million households in the UK. Unlike other plants, you can’t simply “rip it out” as its creeping roots mean it’s extremely hard to eradicate.

Mr Seal said: “It’s a bit like an iceberg. What you can see growing usually isn’t usually a true reflection of the size of the problem.

“If left to its own devices, it spreads quickly and will push up through paths, patios, driveways, drains, and even the cavity walls of homes, causing damage that is costly to repair.”

If you have spied the plant in your back garden, you do not legally have to remove it from your land unless it’s causing a nuisance. However, you can be prosecuted for knowingly letting it spread into the wild.

“It’s not illegal to have it growing on your land, but if you allow it to spread to an adjacent property, you could find yourself on the wrong side of a lengthy and expensive claim for encroachment,” Mr Seal added.

In fact, in a landmark ruling on Japanese knotweed, councils and Network Rail could be forced to pay millions of pounds in cases where the plant has been allowed to stray from their land onto homeowners’ plots, and subsequently decreasing the value of their property.

Knotweed has become less of an issue for lenders

In the past, the presence of knotweed has been the scourge of many property transactions.

David Hollingworth, of broker L&C Mortgages, said: “There was a time when any mention of knotweed in the vicinity of a property could result in an otherwise straightforward mortgage application being declined.”

But, he added, that while the concerns over the plant – and its potential impact on the structural integrity of a property – haven’t entirely gone away, lenders are taking a less black-and-white view.

He said: “Over time, lenders and surveyors have worked to establish a more nuanced approach, recognising that knotweed should not render a property unmortgageable when it’s likely to be a much more manageable and treatable situation. This means knotweed shouldn’t necessarily stop a buyer getting a mortgage, as once it might have done.”

At the start of last year, the Royal Institute of Chartered Surveyors (RICS) scrapped the blunt “7-metre rule” whereby lending restrictions were automatically put in place for any property with knotweed within 7 metres of the boundary.

This was in acknowledgement that the risks associated with the plant were not as dramatic as the industry once thought.

Mark Harris, of broker SPF Private Clients, said: “Knotweed is no longer the death knell it once was. Each lender will take its own approach, but many have adopted the RICS categorisations, which range from one to four.”

Category 1 (the lowest) means knotweed has not been seen on the property, but has been spotted on neighbouring land more than 7 metres away.

Category 4 (the most serious), means knotweed is within 7 metres of the main property. With the latter, details need to be documented in the property’s valuation report, and further investigation by a specialist firm will be required.

Mr Harris added: “All recommended remedial works must then be covered by an insurance-backed guarantee for a minimum of 10 years. This must be property-specific and transferable to subsequent owners. This plan must be confirmed prior to completion, but it is not necessary for the recommended remedial works to have been completed by then.”

While this may sound encouraging, much will still depend on the valuer’s comments.

Andrew Montlake, of Coreco, another broker, said: “Knotweed is not quite the deal-killer it once was, but if found near the property, it can still cause a headache.

“Different lenders will take different views, and there are still some which may decline the application altogether.”

Strict rules for sellers

It’s important to know that it is illegal to sell a property without disclosing the presence of knotweed.

As a seller, you must complete the Law Society’s TA6 form which asks a direct question about whether a property is affected by knotweed.

Mr Seal said: “Anyone buying a property has the right to know if it’s present, as that could impact their decision to buy, and the price they’re willing to pay.”

The key is to be transparent.

Mr Montlake said: “We have heard cases where sellers have tried to hide the plant. But there is always a risk this could come back and bite if it has been deliberately hidden and a buyer decides to take legal action.”

New findings from a YouGov survey commissioned by Environet show nearly two-thirds of people would consider taking legal action against the seller if knotweed was found on a property after they moved in, and it hadn’t been declared.

Mr Montlake added: “Experience over 20 years tells me those vendors who are honest upfront have the best chance of success. The best approach is to answer questions truthfully, and also to start a programme of works to mitigate the risk sooner rather than later.”

How to get rid of Japanese knotweed

If you are looking to get rid of the plant, you will need deep pockets.

As a guide, professional treatment with herbicide could set you back around £1,750, according to CheckaTrade – though in some cases, this figure could be a lot higher.

If full excavation and removal is needed, CheckaTrade puts the average cost at around £6,500, and bills as high as £20,000 are not unheard of.

While herbicide treatment is cheaper, the issue here, according to the experts, is that the plant is simply induced into dormancy, rather than killed off permanently.

Mr Seal said: “The best way to preserve a property’s value and remove the risk of future legal claims is to dig knotweed out of the ground once and for all.”

But this could mean a sizable area of land will need to be dug up, which can cause a lot of upheaval.

Should I be worried about Japanese knotweed as a buyer?

If you find out a property you’re interested in buying has knotweed, then it’s vital you take steps to protect yourself.

Samuel Ewen, of Rosehill Financial Services, said: “It’s best to take extra care when researching a property with knotweed, and be sure to have a private survey carried out.”

You need to be sure the seller has a plan in place to manage it, and it’s also vital to check the firm involved is a reputable one which will be recognised by a potential lender.

To find out if the property you’re hoping to buy is in a high-risk area, you can make use of Environet’s Japanese knotweed heatmap.

Before deciding to go ahead with the purchase, you also need to give some serious thought to whether the knotweed may affect your ability to sell the property further down the line.

So is Japanese knotweed worth worrying about?

While this plant remains one of the UK’s worst weeds, it seems as far as buying and selling homes is concerned, knotweed is no longer the deal-breaker it once was.

Mark Blooman, of B2 Chartered Surveyors, said: “Knotweed remains an issue for lenders, though not an insurmountable one – provided the right steps are taken, and the necessary measures put in place.”