When you think of ASBO’s, garden plants are probably not the first thing to come to mind, but failing to control Japanese Knotweed could land you with an ASBO and a hefty fine. Understand why the plant is such a problem and how to deal with it.

Japanese Knotweed was introduced into Britain by the Victorians as an ornamental plant. Since then the plant has become the country’s most invasive and destructive plant. The secret behind the plants success is its resilience, fast growth rate and extensive root system.

Plants can grow 75mm a day; reach 3m tall and have roots extending up to 7m deep. These extensive roots have been known to grow through cracks and gaps in and around concrete floors of a property, both internally and externally. It has even been found to grow within external wall cavities and within sub-floor voids. Chopping down the plant won’t even stop it – without the correct treatment it can lie dormant for 20 years!

So how do you deal with Japanese Knotweed?

Managing the weed is the responsibility of the owner/occupier of a site who has a legal obligation to prevent it from spreading and know exactly what to do with the weed. So when you encounter it on site here’s what you need to do to ensure minimal delays to your build:

  • Ensure the area is cordoned off where the Knotweed is situated in order to prevent machinery/foot traffic from accidentally spreading the material across the site.
  • Seek specialist guidance, referring to the Environment Agencies code of practice for dealing with Japanese Knotweed on development sites.
  • Follow a Japanese Knotweed Management plan.
  • If herbicide treatment is to be carried out it is essential the contractor is a competent and qualified person and must have appropriate National Proficiency Test Council (NPTC) certification.
  • Obtain a copy of any insurance backed treatment.

As Japanese Knotweed is not a notifiable contaminant there is no cover under the contamination section of the LABC Warranty policy.

For more information on Japanese Knotweed see the Government's guide on managing the plant here.

Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.


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