04 Mar 2015

Untangling the problem of Japanese knotweed


Although a bright and attractive plant, Japanese knotweed is well known for wreaking havoc on building sites, often causing structural damage and costly eradication fees, as well as jeopardising your mortgage eligibility.


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Japanese knotweed is increasingly hitting the headlines, particularly around the new ASBO legislation and the difficulty of raising mortgage finance on property or land that has knotweed present on or near it.

Lenders will only be satisfied if it is professionally eradicated and if the work is covered with an appropriate insurance backed guarantee. Anyone that has come up against this plant will understand why this is required.

While Japanese knotweed poses no threat to human health, its impact on building and development can be considerable. In its insatiable quest for water and light, it will exploit weaknesses in structures including expansion joints in concrete, broken mortar between bricks or paving slabs and weaknesses in asphalt. It can force the layers of cavity walls apart as well as damage drains and sewers.

If you are embarking on a self-build, make sure you familiarise yourself fully on this invasive and pernicious plant.

Your obligations?

In Part C of the Building Regulations – Site Preparation – it states clearly that a site should be adequately prepared to minimise the hazard of damage to the building from existing vegetation, contaminated soil or pre-existing foundations. Under the 2010 updates to the Regulations, site investigation is now recommended in order to determine how much unsuitable material should be removed before building begins. Where Japanese knotweed is concerned, this means determining the extent of the problem and that’s a job for a specialist.

Legal implications

It is not illegal to have the plant growing on your land, but The Wildlife and Countryside Act 1981 and the Environmental Protection Act 1990 make it an offence to let knotweed spread off site. Any soils containing Japanese knotweed must be taken to a registered landfill site authorised to accept Japanese knotweed. Be aware that it is the responsibility of the person consigning the waste to accurately classify it. This means clearly stating it contains Japanese knotweed and ensuring it is taken by a waste carrier registered by the Environment Agency. Waste transfer notes should be obtained to provide an audit trail between consignor, waste carrier and landfill site.


If the plant is encroaching on to your land, you do have some redress in law under civil nuisance. To bring a successful claim you would need to demonstrate that the knotweed originated from the adjoining land and that it is causing you nuisance. It’s not always easy to prove the knotweed origin, but an expert will be able to help. If all else fails, the Home Office issued guidance last October in the Anti-Social Behaviour, Crime and Policing Act 2014 in relation to Japanese knotweed. Failure to comply with the Community Protection Notice could result in a criminal offence and large fines.

Japanese knotweed is not something to be ignored. Early detection, specialist advice and an insurance-backed guarantee on the treatment plan will enable your building project to go ahead.

Further information....

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