Identifying and eradicating Japanese knotweed in the UK built environment

In the UK, Japanese knotweed is an invasive, non‐native plant that has the potential to cause significant damage to buildings, foundations and development sites if left to establish. The plant's bamboo‐like stems can push their way through tarmac and expose weaknesses or cracks in concrete. The purpose of this paper is to investigate the current problems caused by Japanese knotweed within the UK and to ascertain the extent to which the knotweed legislation provides clear enough guidelines and measures, and, if not, how this could be addressed.

A literature review and interviews have investigated the current and future eradication and control techniques available for Japanese knotweed. The primary and secondary research conducted has incorporated the views and opinions of experienced Japanese knotweed experts. Case studies of sites infested with knotweed have also been carried out.

The study has identified and recommended that both public and professional awareness of Japanese knotweed still needs to be increased, throughout the UK. A detailed identification card has therefore been produced as part of this study, in order to show the different growth stages of the invasive plant, throughout the year. The study has demonstrated that an eradication technique must be carefully chosen and tailored to suit each infested site after a full site survey. The semi‐structured interviews have established that the current legislation, guidance notes and also the “Knotweed Code of Practice” produced by the Environmental Agency, provide adequate guidance on controlling Japanese knotweed. The research highlighted that knotweed spreading from neighbouring properties was a potential problem, but in practice, neighbours usually reach mutual agreement to avoid high legal costs.

Japanese knotweed is an increasing problem in the UK and this research will increase the awareness of those instructed to inspect property or development sites where infestation may have occurred. Professionals within the construction industry including surveyors, estate agents, developers and project managers will all find this paper of benefit.