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Cannabis farms – the threat to property owners

Risk & Analytics|Corporate Risk Tools and Technology|Property|Risk Management Consulting
COVID 19 Coronavirus

By Syed Islam | August 5, 2020

This article talks about the potential risks of cannabis farms appearing at vacant properties during COVID-19.

Property owners will consider many different things and tick many boxes in order to protect their assets. However, the thought of their property being used by criminal gangs to cultivate cannabis is perhaps unlikely to cross their minds.

UK statistics show that numbers have however been rising on rental properties that have been targeted by gangs looking to house their criminal activities. According to the Home Office, more than a third of a million cannabis plants were seized in 20181. In the same year the Metropolitan Police revealed that one cannabis farm was found every couple of days in London. In a short period of four years, cannabis farms detected by the police have increased by more than 150%2. Figures released in 2019 by the London Fire Brigade show there were 12 cannabis factory fires in London in the first four months. In comparison, the total in 2018 was 15 throughout3. The majority of these fires were in residential properties posing a significant threat to neighbouring lives and properties.

The demand for cannabis whether it be for medicinal or recreational use is increasing. Gangs of cannabis cultivators are using more inventive ways to conceal cannabis grows – not just in residential homes, but surprisingly in large partially-occupied office buildings, back of commercial shops, commercial units and even a pub basement. Other than the social implications, cannabis farms present a serious problem to property owners. They are very dangerous places and pose a serious risk of fire. Often the electricity has been bypassed and seriously overloaded – circuits run close to water-filled pipes. Plants grown upstairs in a building can also cause floorboards to rot, presenting the danger of collapse.

What is the fire risk?

A large warehouse blaze in Tottenham in May 2019 was believed to have started in a cannabis factory spreading to adjoining units. The ferocious blaze caused thick plumes of smoke to bellow into the sky prompting the attending brigade to warn residents to keep windows and doors closed. London Fire Brigade Deputy Commissioner and Director of Operations Tom George said: “Cannabis factory fires are very dangerous due to criminals using unsafe wiring to illegally obtain electricity to grow the plants. They’re often in top floors or lofts which means when a fire takes hold it spreads, destroying roofs and damaging neighbouring buildings”.

“They pose a significant risk to our firefighters who tackle the fires and also to the people living within close proximity to them.

We are therefore asking for members of the public to take action by knowing what the signs are and to inform the police so they can act swiftly to prevent these dangerous fires.” London Fire Brigade is extremely concerned about the rise of these fires and are asking people to look out for the signs of cannabis factories and to report any concerns to the police.

What precautions should be taken?

Property owners, landlords and managing agents are encouraged to take precautions to protect their properties, including regular site inspections and keeping a log of inspections. Some of the tell-tale signs clients and managing agents should be looking out for are:

  • There's a strong, sickly smell - It might sound obvious, but most cannabis grows are discovered by passers-by or keen-nosed residents catching a whiff of the drug's distinctive smell. Police have even handed out scratch-and-sniff cards to help people recognise the scent
  • High levels of condensation – Landlords might notice damp on the walls or peeling wallpaper, while from the outside a neighbour might spot condensation on the windows, even when it's not the depths of winter. The condensation may well be due to inside having been turned into a makeshift greenhouse
  • Snow doesn't settle on the roof - Cannabis factories produce a lot of heat, which can cause tell-tales signs, especially in winter. When it snows, the roofs of cannabis farms can be obvious as the snow melts, meaning it is probably the only house on the street without a snow-covered roof. Birds also like roosting on a nice warm roof
  • Strong, constant lighting day and night - Cannabis needs light to grow, so watch out for properties with bright lighting at all times of the day and night. Lights will often be on a timer switch, coming on in the middle of the night
  • Lots of visitors and at unsociable hours - Frequent and varied visitors to a property, often at unusual times could mean you just have a popular neighbour with a big family. But if unfamiliar faces are turning up next-door day and night, it might be a sign that there’s something more sinister going on. One thing to watch for is lots of new faces coming knocking
  • Constant buzz of ventilation - If you can hear the constant noise of a fan, chances are it could be acting as ventilation for the cannabis grow.
  • Rocketing electricity bills - The lights, dehumidifiers, hydroponic systems and heaters take a lot of electricity. Many farms have been found where drugs gangs have hacked into the electricity wires before the meter to that individual house, and so bypassed having to pay for the electricity. If you are a landlord who gets a copy of the bill, has it dropped or gone up suddenly? If so, your neighbourhood growers could have tapped into your supply and are charging you to power their drug operation. You should contact your supplier and the police immediately
  • Excessive security - Growers live in constant fear that their home-grown farms will be discovered by police, landlords or rival drug dealers. If there are padlocks on the gates, massive grilles and double and triple locks on the doors, that should raise eyebrows – especially if the street is relatively safe. On bigger, high value farms, portcullises, bars on the windows and even CCTV cameras can be evident
  • Windows are constantly covered - Do your neighbours have the curtains drawn all day long? It might make it look like the house is unoccupied, but having windows blocked up with panelling or sheeting would suggest there’s something they don’t want you to see. This could be a sign that there are many budding plants inside soaking up bright artificial light.

For any further information or guidance on property precautions and security measures for vacant units please contact your Willis Towers Watson representative or Syed Islam.

Please visit the Willis Towers Watson COVID-19 hub for the latest information and guidance.


Each applicable policy of insurance must be reviewed to determine the extent, if any, of coverage for COVID-19. Coverage may vary depending on the jurisdiction and circumstances. For global client programs it is critical to consider all local operations and how policies may or may not include COVID-19 coverage.

The information contained herein is not intended to constitute legal or other professional advice and should not be relied upon in lieu of consultation with your own legal and/or other professional advisors. Some of the information in this publication may be compiled by third party sources we consider to be reliable, however we do not guarantee and are not responsible for the accuracy of such information. We assume no duty in contract, tort, or otherwise in connection with this publication and expressly disclaim, to the fullest extent permitted by law, any liability in connection with this publication. Willis Towers Watson offers insurance-related services through its appropriately licensed entities in each jurisdiction in which it operates.

COVID-19 is a rapidly evolving situation and changes are occurring frequently. The information given in this publication is believed to be accurate at the date of publication shown at the top of this document. This information may have subsequently changed or have been superseded, and should not be relied upon to be accurate or suitable after this date.




Cert CII, Risk Management Executive

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