Japanese Knotweed is considered to be one of the most invasive plants in Britain but would you recognise it if you came across it on a site?

Image courtesy of nonnativespecies.org

Can you recognise it just from its roots or in winter? 

The photos here highlight what to look out for:

If Japanese Knotweed is left untreated or is incorrectly treated then the potential for regrowth can be extremely high. Japanese Knotweed can grow through and cause damage to paved and tarmac surfaces and also to drainage. Whilst it's not known for growing through concrete it can grow both internally and externally in a property through cracks and gaps in and around the concrete finishes/ floors. In addition it's been found to grow within external wall cavities and within sub-floor voids.

You don’t have to remove Japanese knotweed from your land, but you could be prosecuted or given a community protection notice for causing a nuisance if you allow it to spread onto anyone else’s property. You could also be fined up to £5,000 or be sent to prison for up to 2 years if you allow contaminated soil or plant material from any waste you transfer to spread into the wild.

Here is a quick guide to the dos and don'ts

If Japanese Knotweed is found on the site you must:

  • Cordon off the area where the Knotweed is situated so that machinery/foot traffic doesn’t accidentally spread the material across the site.
  • Obtain specialist guidance, referring to the Environment Agencies code of practice below.
  • Obtain and follow a copy of the Japanese Knotweed Management plan. 
  • If a herbicide treatment is to be carried out it's essential that the contractor used is competent and has appropriate National Proficiency Test Council (NPTC) certification.
  • Get a copy of any insurance backed treatment.

Find out more

Although withdrawn as an Agency document in July 2016 the Environment Agency’s guide to Managing Japanese Knotweed on Development Sites (Amended July 2013) is still a good source of information. - Managing Japanese knotweed on development sites

Sources: http://www.nonnativespecies.org/index.cfm?sectionid=47



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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