What is Japanese knotweed?

Japanese knotweed, which was introduced to the UK in the 19th century as an ornamental plant, has now spread to become the most invasive plant in the UK and a real threat to the structure of UK buildings.  The plant spreads rapidly (up to 10cm per day some months!) by its roots and stems, and is extremely difficult to eradicate from land.  Due to its vigorous roots and top growth which penetrate foundations, concrete and walls the plant is now causing considerable damage to properties across the UK.  Added to this, the costs of knotweed removal and treatment are substantial and must be performed correctly, as if even a small piece of root or stem is left in the ground the plant can re-establish itself.  To add some perspective to the potential for costly removal works, the eradication of Japanese knotweed from the Olympic Park in Stratford, London is thought to have cost approximately £70 million.

How Japanese knotweed may affect a property transaction

First and foremost many buyers and lenders are wary of proceeding with purchases of affected properties due to the threat of physical damage to the structure and the subsequent effects on value, and the costs of removing the plant and of obtaining bespoke insurance to cover such risks.  Any presence will need to be reported to a lender, which may decline to lend on the property depending on the extent and location of the infestation and the value of the property.

Also, whilst it is not an offence to have Japanese knotweed on your property, it is an offence to plant it or cause it to grow in the wild.  This latter offence includes a failure to take reasonable measures to control the knotweed resulting in it spreading to the wild, which could leave the offender facing a fine of up to £5,000 or even imprisonment.  Whilst it is unclear as to whether the knotweed is treated as a contaminative material, a local authority can also require an occupier of the land to remedy the land if it considers the knotweed is likely to affect adjoining land.

These risks are all concerns for a buyer.  Whilst the starting point of ‘Buyer Beware’ means that the seller is not under a duty to disclose the presence of knotweed, standard enquiries used in property transactions, and to which a buyer can both expect and rely upon an answer, do enquire further – commercial property enquiries request details of any environmental problems or infestations, though a commercial buyer should consider asking specifically whether there is any knotweed, as is done in residential enquiry forms.  A seller, especially of commercial property, may simply respond to enquiries by asking the buyer to rely on its searches and its own survey.  The problem with relying on searches is that Japanese knotweed is not usually covered in environmental reports.  As is always the case, buyers should view the land and perform a survey (though note that the knotweed does die back in winter).  If there looks to be a presence, a specialist report may be obtained which may provide an estimate of removal costs.

If a property is infested with Japanese knotweed, a buyer may seek a price reduction to cover the cost of removing and disposing of it, and an indemnity to protect it from any claims from neighbours (though an indemnity cannot remove any criminal liability).  If previous works have cleared knotweed, a buyer should request a guarantee of these works given the propensity for the plant to return if clearance is not performed correctly.

Any other risks?

In addition to the costs of clean up, impact on marketability and the criminal offences of planting or causing to grow Japanese knotweed, the presence of it on your land has the potential to land you in even more hot water.  As the knotweed will be treated as controlled waste, this will need to be removed in a controlled manner with registered carriers to avoid further fines and the threat of imprisonment.  An owner affected by knotweed may also face a private nuisance claim from neighbours concerned that the plant has encroached onto their land and caused damage or otherwise interfered with their enjoyment of the land.

Common sense steps

Given the risks associated with Japanese knotweed, buyers should always perform a survey which may reveal the presence of the knotweed and both parties should keep an eye on what is growing on their properties and surrounding properties.  The knotweed, however, should not be ignored.