Please Note: This Article is 5 years old. This increases the likelihood that some or all of it's content is now outdated.

As a landlord it can be easy to miss impacts on your property investment due to your not being there all the time. As inspections are carried out periodically, and aren’t always extensive, you are often reliant on your tenants reporting defects as they notice them, which is far from ideal.

Most of us are familiar with structural issues and these can often be picked up during inspections, but how many landlords, or building surveyors for that matter, are confident that they could identify risks caused by invasive weeds?

The Wildlife and Countryside Act 1981 (as amended) lists over 40 non-native invasive weeds that could get you prosecuted if you allow them to spread. However, of these, Japanese knotweed is by far the most significant in terms of causing property impacts.

Where did it come from?

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Japanese knotweed was introduced to the UK in the early half of the 19th Century by Victorian botanists who valued its attractive, bamboo-like stems and clusters of late blooming flowers. However, by the end of the 19th Century it was apparent that the plant was aggressively invasive and had escaped to many locations where it was not wanted, becoming established on areas of waste ground and along railways, canals, rivers and roadsides.

The reason it was so invasive is that it was brought to the UK without any of the controlling organisms that keep it in check in Japan; things like diseases, insects and animals that eat it, and other plants that compete with it. As such, knotweed’s naturally invasive characteristics were able to flourish uncontrollably, resulting in it becoming so widespread today.

Thankfully, the Victorians only brought a female plant across, which means that there is no pollen for viable seeds to be produced. However, this serves to illustrate how effectively it has spread from small root fragments in contaminated soil.

Its ease of spread from such root cuttings is enhanced by the fact that its root system spreads several metres from the aboveground stems and can penetrate a few metres deep into the underlying soil. This makes it easy for an unwitting gardener to fragment and spread root pieces when soil is excavated many metres from where the stems sprout from the ground.

How does it affect property?

Knotweed has become a people and property issue, rather than the ecological problem that the Wildlife and Countryside Act sought to solve. Its vigorous rate of growth and ease of spreading in nutrient poor soils and in and amongst hard standing surfaces can cause significant damage to paths, walls, fences and buildings. However, these effects are usually minor, save for some extreme examples.

The main impact on property owners is the blighting effect that knotweed can cause, resulting in potentially huge reductions in property values.

This stems from lender’s reluctance to offer mortgages on knotweed affected property and is exacerbated by the plants spreading underground several metres from where the stems are visible. Guidance from the Royal Institution of Chartered Surveyors (RICS) states that any growth within 7m of a property boundary should be considered a risk. At such a distance, a small clump of knotweed in the corner of a back garden could be affecting four of more adjacent properties.

Such a small clump of stems could easily be missed by a landlord who doesn’t inspect their or their neighbours’ gardens on a regular basis. In the past, surveyors valuing properties for lenders probably missed small knotweed infestations in a similar way. However, with the production of the RICS guidance and following the huge media interest, it is more likely now that someone will notice knotweed at a time when it will cause most impact in terms of diminution in value of property. Recent litigation cases have been based on property value reductions of between 5% and 20%, which can amount to hundreds of thousands of pounds

What is the legal situation?

As it has evolved into a people and property issue, Japanese knotweed rarely invokes action via the Wildlife and Countryside Act. Currently, the main threat from the police to landlords and other property owners who allow knotweed to grow on their land is receipt of a Community Protection Notice (i.e. an ‘ASBO’) through newly reformed anti-social behaviour legislation aimed at knotweed in particular.

In terms of civil law, the potential costs are much more significant. The knotweed litigation market is burgeoning. This is because so many people are poetically affected by a relatively small patch of knotweed on their property. If you have knotweed in your garden and it is within 7m of several other properties then you could be putting all those properties’ mortgages at risk. In turn, the damages that those property owners could claim from you could run into hundreds of thousands of pounds. It is therefore vital that landlords identify knotweed risks on their properties as soon as possible and seek to get the problem resolved before their neighbours start suing them.

What is the solution?

Thankfully, the solution for the vast majority of knotweed infestations is simple. Herbicides applied to stems and leaves over several years will solve most problems. However, any such work needs to be completed by an appropriately qualified contractor who is a member of the Property Care Association Invasive Weed Control Group (PCA IWCG). This body sets the professional benchmark for knotweed control firms and was formed at the request of the Council of Mortgage Lenders (CML) and the Building Societies Association (BSA), who are the lenders’ trade bodies. The CML and BSA also required surveyors to be trained on how to identify and gauge knotweed risk to property. This was realised by the publication of the RICS guidance.

Where knotweed more seriously affects property or where construction works in affected grounds are to be carried out, a more immediate solution is required. This can require the full excavation and disposal of the affected soil, which can be very expensive due to the high costs of knotweed haulage and the large volumes of waste generated by the often deep and extensive roots. As such, even a small clump of knotweed can cost £10,000 or more to remove. However, compared to the often much greater reduction in value of property caused by knotweed, this can be a cost-effective approach.

There are also cheaper methods of control that have more immediate impact than herbicides, such as reduced excavations and the use of root barrier membranes or the selective screening of roots from contaminated soils in order to reduce waste volumes. I found a really useful resource with regards to various Japanese knotweed removal options, which is excellent.

Summary advice for landlords

Japanese knotweed rarely causes structural damage. However, the blighting effect on property value and the legal implications can be very expensive indeed. The risk of this happening is elevated if landlords are reactive and not proactive in managing the risks that affect their property investments.

Below is a summary of the important points that landlords should be aware of with regard to Japanese knotweed:

  • Check your properties for knotweed (this includes all land within 7m of boundaries!)
  • Use knotweed identification guidance
  • Appoint an expert knotweed surveyor if you are at all
  • If you find knotweed, deal with it now, as waiting can increase costs and risk!
  • If you are affected by knotweed on adjacent land you could have a legal case to claim damages and get it sorted
Please Note: This Article is 5 years old. This increases the likelihood that some or all of it's content is now outdated.


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