Japanese knotweed can affect homeownership and the value of a property. The seller or estate agent may have informed you, or the seller may have disclosed it as part of the standard law society conveyancing forms. Your surveyor may have identified the plant. A property with knotweed shouldn’t necessarily be avoided altogether but it will mean you will take on the responsibility of controlling it and ensuring it does not spread outside the boundaries of the property you are purchasing. If you are buying with a mortgage, you will need to check what your lender’s position is.
The plant originates from Japan, China and Korea and is a very fast-growing perennial, with tall, dense annual stems. Stem growth is renewed each year from the deeply-penetrating rhizomes (creeping underground stems). The leaves are heart or shield-shaped with an alternate leafing pattern along the stems. In winter, the plant dies back to ground level but by early summer the bamboo-like stems emerge from the rhizomes to shoot to over 7 foot, suppressing all other plant growth. There are a few lookalike (but harmless) plants – so it is always advisable to get an expert to confirm whether it is present.
Why is the plant such a cause for concern? If left unchecked, it can cause structural damage to properties, weaken foundations and grow through walls and drains. It can take several years to control through a ‘management and treatment plan’. Excavation of the rhizome (root) from a property can be an effective method of remediating the problem. However, removal of the rhizome from the soil can be difficult to achieve as a thumb sized piece of rhizome can lead to new growth and the spread of the plant. Japanese knotweed should always be dealt with by a professional and requires treatment with either herbicide over 2 to 3 years or by excavation. Homeowners must not dig it up and dispose of it themselves otherwise they could commit an offence under the Environmental Protection Act 1990, for failure to safely dispose of controlled waste.
If you are buying the property with a mortgage, some lenders will proceed if it can be shown that it is being controlled or it has been excavated. Other lenders may refuse to deal with properties which have an ongoing Japanese knotweed infestation. In many cases, lenders will expect a knotweed ‘management and treatment plan’ to be in place by an approved contractor, accompanied by a 10-year insurance-backed guarantee on completion of the treatment. The aim of such a plan is to safeguard the home against knotweed for a set number of years. You will be advised on this documentation as part of the conveyancing process. Insurance-backed treatment certificates give you the confidence knowing that if the plant returns, then a company will be bound to finish the eradication.
What happens if there is knotweed on neighbouring land? Neighbours are under no obligation to eradicate it on their own land although they will be breaking the law if they allow it to spread onto other land. If the neighbouring property is infested the plant could spread onto the property you are purchasing. You could claim the costs of removal from your neighbour however this process can take time and the property you are purchasing would then be classed as being affected by Japanese knotweed. It is important you inform your conveyancer and surveyor if you aware of neighbouring land being affected by the plant.
You should carefully consider the severity of the infestation and the impact on the value of the property, with the assistance of a surveyor. If the property is by/near a railway extra care should be taken to check the weed is not growing alongside the train tracks and creeping onto the Property. Each case should be looked at on an individual basis and you should find out as must about the Japanese knotweed before making any decisions. In some circumstances, it will be advisable to have a Japanese knotweed survey undertaken to obtain an estimate for the cost of removal. In other situations, it may be appropriate to seek to negotiate a lower price for the property to reflect the cost of treatment and the “knotweed stigma”.
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