Japanese knotweed: the plant that could cost you your home

Japanese knotweed: the plant that could cost you your home

Japanese knotweed may look harmless enough, but it could cost you your home

Christina Jordan

Mortgages and Home

Christina Jordan
Updated on 24 June 2013

If, like me, you are not particularly green-fingered, you might think that one plant looks pretty much like another. In which case you are in danger of missing a silent assassin gaining strength within your garden.

Japanese knotweed looks like lots of other weeds to the untrained eye, but it has the power to ruin your home and cost you thousands of pounds.

Pity the couple in Hertfordshire that were told a couple of years ago that their £300,000 four-bed Hertfordshire home needed to be demolished in order to treat the scourge of Japanese knotweed that had penetrated their walls.

The plant had spread from waste ground near the newly-built property and quickly advanced the length of the garden to enter their home through walls and skirting boards. Surveyors told them that the value of the property had dropped to just £50,000, and that the only way to effectively remove the scourge was to knock the house down, treat the plant and then rebuild.

And imagine the disappointment of the home seller who saw his deal fall through within weeks of exchange because a tiny 3cm piece of Japanese knotweed had been found in his garden. His buyer’s lender panicked and refused to lend the mortgage.

These are clearly extreme examples but Japanese knotweed is almost always a problem for homeowners (and potentially their neighbours).

What exactly is it?

Japanese knotweed has been in the UK since the 1800s, having been introduced as an ornamental plant by the Victorians.

It looks pretty innocuous, like many plants or weeds, and is described by the Environment Agency as lush green in colour with shovel shaped leaves and a stem that looks like bamboo. It also produces white flowers in autumn and grows rapidly, up to 10cm a day.

It spreads like wildfire through its stems underground, growing a metre in a month and potentially causing heave below buildings.

Once the concrete or tarmac cracks from the heave, the plant has a way into your home, working its way through the tiny gaps and potentially causing structural damage or blocking drains. It’s the most invasive plant in the UK and very persistent indeed.

What to do about it?

Whatever you do, don’t ignore it. Japanese knotweed grows rapidly and if it infects your neighbours’ gardens and properties you could be liable for damages. So if you see it in your garden, deal it with properly and quickly.

You need to focus on stopping the plant spreading and getting rid of it. Believe it or not the Environment Agency takes this problem so seriously it has produced a knotweed code of practice to guide those involved in the disposal of the plant through the specific measures that should be undertaken.

It’s targeted towards firms that are involved in the disposal of the plant, but if you have Japanese knotweed on your land it is still essential reading, as it will give you an idea of what you should expect any professionals you employ to be doing.

Key things to be aware of are:

  • If you are having the weed fully excavated and disposed of, any contractor you employ needs to be registered with the Environment Agency as a waste carrier. The agency’s website also allows you to search for contractors in your area on its Waste Directory.
  • You can also treat the knotweed more slowly with a combination of herbicide treatment and careful excavation if you have no urgent need to get rid of it. But this will take at least three years and you will still have to dispose of the soil in line with the code of practice mentioned above. Plus you should still get a qualified person to carry out the treatment and if you live near a river or stream, you need permission from the Environment Agency before using any chemicals.
  • You can burn the waste from Japanese knotweed but you should inform your Local Authority and pay heed to best practice guidelines.
  • Soil containing burnt remains of Japanese knotweed may also be buried on the site where it was produced, but very specific guidelines need to be adhered to. Plus you need to inform the Environment Agency a week in advance if burying the waste from your knotweed.

As you can see, there are a lot of hoops to jump through to get rid of this plant properly and it’s little wonder many people pay a contractor to ensure the job is done properly.

[SPOTLIGHT]But what should you do if you notice this plant and you are about to sell your home? Do you need to go through all of these measures first, or can you sell up with the knotweed in your garden?

Alternatively, can you take a risk and just cut it down the day before the viewings and the survey and hope for the best?

Be upfront

To be blunt, if you are trying to sell your home and you discover Japanese knotweed in your garden, it is likely to cause you problems. Some buyers won’t touch a house if they know this plant is in the garden, or even neighbouring gardens. And even those that are willing to deal with it may find their mortgage lender will not offer them a loan once they learn of it, because of its potential to cause damage.

But it’s not all bad news. According to the Council of Mortgage Lenders many lenders will now consider lending on a property with Japanese knotweed (and they expect their surveyor to spot it during the valuation). They usually consider applications on a case-by-case basis and look for evidence of an initial treatment, with a commitment to an ongoing treatment programme.

Another reason not to contemplate hiding the presence of Japanese knotweed in your garden is that the Property Information Form used during the property sale transaction has recently been updated to specifically ask a question about it.

As I explained in What to declare when selling your home if you lie on this form you are leaving yourself open to a misrepresentation claim from your buyer, since the documents form part of the pre-contract enquiries and are legally binding.

Japanese knotweed can be a major problem for homeowners but it can also be dealt with if caught early and treated effectively by an experienced contractor. If you have the weed in your garden, tackle it head on because, one thing is certain, it won’t go away without a fight!

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