What to check before buying a home with Japanese knotweed

Updated: March 27, 2018

Failing to spot Japanese Knotweed in the garden of a home you plan to buy could result in you wasting time and money only for your lender to decline your mortgage. Worse still, you may end up buying a property that you cannot re-sell.

Thoroughly check the garden

There are good reasons for taking a closer interest in what's growing in the garden. In recent years many homes have been affected by certain invasive plants, particularly Japanese Knotweed (or Fallopia japonica to botanists.)

See also: Japanese Knotweed? What to do before selling your home.

What is Japanese Knotweed?

Japanese Knotweed is a highly invasive plant that has received a considerable amount of negative press over the past decade.

The plant's roots can cause considerable damage to property. As a result its existence is of concern to homebuyers and mortgage lenders.

These are some of the problems that have arisen:

• Damage and blockage to drains and other buried services
• Collapse of boundary or garden walls
• Buckling and other damage to drives, patio and similar paved areas
• Damage to the foundations of conservatories, outbuildings and even house foundations (especially older properties which often have much shallower foundations than modern homes.)

Bamboo like plant

Japanese Knotweed is a bamboo-like plant that was introduced into the UK in the 19th century as an ornamental plant. It became popular with landscape gardeners not just because of its appearance but because it grows rapidly and could therefore cover large areas quickly.

Because of the way it spreads by its root system it can quickly travel from one garden to several others, causing damage to several properties. It is no longer confined to the large country gardens where it was originally grown but can now be found in ordinary suburban gardens in many parts of the country.

Mortgage lenders may refuse to lend

There are also other consequences for property buyers if Japanese Knotweed is growing on the property. Mortgage lenders may refuse to lend if the plant is known to be growing on the property or may retain part of the advance until it has been properly eradicated.

Find out your lenders position as early as possible. You do not need to alert the lender - you can check online. Lenders publish their lending requirements in the Council of Mortgage Lenders (CML) handbook.

Japanese Knotweed is addressed in the Part 2 section. An example of the lending requirements for the HSBC can be found here.

It is also likely that any damage to buildings and drains will not be covered by buildings insurance.

There are also some potential legal consequences as it a criminal offence under the Wildlife and Countryside Act 1981 to knowingly allow Knotweed to spread from your property.

Furthermore the 'Anti-Social Behaviour, Crime and Policing Act 2014' provides that community protection notices can be used to force landowners to control non-native invasive plants (which includes Knotweed) on their property. Fines can be imposed for non-compliance with such notices.

Difficult to eradicate

One of the reasons that Japanese Knotweed is such a problem for property owners is that it is extremely difficult to eradicate. Giving the plant a quick spray with the usual garden weedkillers won't be enough to kill it.

It is also very difficult to dig up – leave even a small piece in the ground and it will rapidly spread again.

The Royal Institution of Chartered Surveyors (RICS) states that it would be necessary to excavate the ground completely up to 3m vertically and up to 7m horizontally from the above-ground growth, resulting in large volumes of waste soil.

The plants together with the excavated soil must be disposed of as 'controlled waste' in accordance with relevant regulations.

Apart from the expense excavating such a large amount of soil is clearly impossible in the usual residential garden, especially when the plant has spread to several properties.

The alternative method of eradication is chemical treatment, using a specialist herbicide that has to be applied by approved contractors. However such treatment can take three years or more to be totally effective.

Identifying Japanese Knotweed at a property before you buy it

We do not seriously suggest that you spend too much time trying to identify all the plants growing in the garden of any property you are looking in. One of the problems in identifying Japanese Knotweed is that its appearance changes over the seasons.

Cases have also come to light where sellers, knowing they have a problem, have just cut down the plant at ground level and then laid turf to cover any signs of the plant. It will quickly re-grow but by then the seller hopes to have sold the property to an unsuspecting buyer.

Ask the seller

It is therefore recommended that you specifically ask sellers whether they are aware of the plant growing on their property or on neighbouring property. Sellers will in any event be required to give information about this when completing the usual Property Information Form.

Giving incorrect or misleading information can amount to misrepresentation.

Building surveyors have also been advised by the RICS to be alert to the presence of Knotweed on any property they are inspecting.

Get a survey, but...

In this context it is always recommended that buyers commission a full building survey rather than just relying on the mortgage valuation. In some cases a further inspection by a suitable expert may be required.

Be warned...

Some surveyors have been slow on the uptake where Knotweed is concerned. Some RICS surveyors are seemingly oblivious to the risk and still do not inspect the gardens thoroughly. It is strongly advised that you commission a full Building Survey rather than a less comprehensive 'Homebuyer Report'.

Before you instruct the surveyor, confirm that he will inspect the gardens and is familiar Knotweed.

Should you pull out?

The existence of Knotweed does not necessarily mean that you shouldn't buy it. If it is already subject to an eradication management programme then there should not be any problem in getting a mortgage.

As soon as you discover that there is Knotweed at the property, you should call your lender and ask what their position is. You can also look at the CML handbook.

This is far preferable to waiting for the seller's solicitor to supply the information which could take weeks or even months.

If Knotweed is present, you can insist that your buyer initiates and pays for the treatment program before exchange. Note that most lenders will require that any treatment program (that typically takes 3 years to complete) is paid for up front in its entirety.

Alternatively (and assuming the lender agrees), it may be a question of agreeing some reduction in the asking price to cover the cost of future treatment, if the property is otherwise satisfactory.

Speak to your solicitor

Get advice from your solicitor at the earliest possible stage.  Solicitors deal with knotweed situations all the time and their advice tends to be pragmatic.  Early advice can save you a significant amount of time money in the long run.

If you are buying a house or flat, read our invaluable guide on 'How to compare conveyancing quotes in 2018'.