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Japanese knotweed is one of the most invasive plants in the UK and commonly causes financial difficulties for homeowners and building developers, particularly when plans have been made to build on the infected land. Although Japanese knotweed is now well-documented, homeowners and builders still find themselves in situations requiring legal guidance and often professional help. Despite further developments in knotweed law and the efforts of environmental agencies, landowners are often left unsure where they stand when building on land infested with Japanese knotweed.
Though Japanese Knotweed is unlikely to cause damage to buildings directly through subsidence or collapse, it does cause extensive damage through its huge underground rhizome (root system). The enormous pressures exerted from them mean they have the ability to push through boundary walls, underground drain systems and even asphalt walkways & drives.
As a result of this, land with Japanese Knotweed often causes significant delays and costs to building developments. The key to navigating these murky waters is understanding how to efficiently identify and remove Japanese Knotweed from your land.
So, Can you build on land that's contaminated with Japanese Knotweed?
For new buildings to be legally constructed on land with Japanese knotweed, the presence of the plant must be announced as part of the building planning process. In some recent cases, building developers have ignored or hidden the presence of Japanese knotweed on their land, in order to avoid slowing construction time and speed up the sale of the finished property.
Currently, development companies are not required to fill out the TA6 property form as part of the process in selling their property, allowing them to lie freely about any potential Japanese knotweed infestation. This legal loophole has allowed developers to complete projects and then sell these on to unsuspecting homeowners, completely unaware that they are buying a property infected by the invasive plant.
Homebuyers can protect themselves by asking their conveyancing solicitor to request a TA6 property form, which requires the developer to confirm if there is any history of Japanese knotweed on the site.
Is a Japanese Knotweed survey required before building work can begin?
You are not required by law to perform a Japanese knotweed survey on land affected by Japanese Knotweed before proceeding with development. However, if there’s a suspicion land is infected by the invasive perennial, it’s within the property developer/home owner’s best interest to have a survey. To prevent any future financial impacts or time wasted on repairs, early identification and treatment of Japanese Knotweed infestations are the most efficient ways of dealing with it.
Ecological experts or chartered surveyors can confirm or deny the presence of Japanese knotweed on a property by completing a site wide ‘Japanese Knotweed Survey’. In addition to identifying Japanese knotweed, a survey can help you analyse the extent that JK affects land and surrounding property. That information could then impact any plans you have for building or renovating.
If a Japanese Knotweed survey shows that Japanese knotweed has been discovered in a small, isolated patch, it may be possible for this area of land to be sectioned off during construction so that building can continue around it. Should the infestation be found to be widespread, controlled excavations might be needed to remove any Japanese Knotweed before construction can begin.
Is planning permission required to develop on Japanese Knotweed infested land?
You need planning permission before you start development of any land—including land with Japanese knotweed on. Most borough councils will have policies regarding the control of Japanese knotweed, and will likely be aware of local hotspot areas. Ignoring the presence of land with Japanese Knotweed and choosing to move soil contaminated is a criminal offence under the Wildlife and Countryside Act 1981, which can lead to a hefty fine and even a prison sentence.
If you own land that is infected by Japanese knotweed, it is recommended that you outline specific actions in your planning application to show how you plan to deal with the infestation. Your plans should highlight how the infestation of knotweed will be managed throughout the development. These plans should include: (1) an assessment of control options, (2) criteria for the completion of control measures and (3) details on how those working on the site will prevent the spread of the invasive plant species.
Should treatment take place before the development of land affected by Japanese Knotweed?
It is necessary to remove Japanese knotweed from any land affected by Japanese Knotweed that is going to be used for building. In severe cases, it might be necessary to remove the weed before construction can begin. The rhizomes of Japanese Knotweed can extend up to 7 meters from where the plant visibly emerges above ground, meaning large infestations may have spread underground much further than first appearances would suggest. Because of their tenacious growth patterns and seasonal growth spurts, entire plants may need to be removed to prevent interfering with your foundations or causing any structural weaknesses.
There a number of laws that control the removal of Japanese knotweed contaminated waste, additionally, building contractors are subject to more regulations that private landowners. In order to avoid being handed fines, developers should ensure that a registered waste disposal company is assigned the task of removing of any contaminated soil. Never attempt to remove any contaminated soil or waste by yourself. Doing so could spread the infestation and be a breach of UK law.
Can development take place on land that’s undergoing treatment for Japanese Knotweed?
Depending on the size of your infestation, the treatment type, and the planned development you wish to pursue, it may be possible to build on land with Japanese knotweed while it is being treated. Sadly, if an infestation is restricted to a small area of land or spread across larger pieces of land, it might be that all development is put on hold until successful Japanese Knotweed treatment has been completed. Your Japanese Knotweed survey will inform you of the exact details of your infestation, including the steps required for safe removal. The survey should be provided as part of the planning permission, allowing for guidance or requirements for waiting on completion of treatment to be made clear.
How do I identify and remove Japanese Knotweed?
If you suspect you have an infestation of Japanese Knotweed on your land, it’s best to call in a professional surveyor to accurately identify the plant. Preventing you from wasting time, money and effort. Early removal of Japanese knotweed depends on qualified experts and the plant being caught before its rhizomes spread.
To remove the Japanese Knotweed infestation itself, you should call in professionals. There are few legal methods of destroying the plant, so it is almost impossible to completely and safely remove the infestation without causing further spread.
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