Hello. I am on the verge of purchasing a property that has Japanese Knotweed (JKW) in the rear garden. The owner's solicitor shared the JKW survey report from mid-2018 that shows 2 affected areas in this pretty long garden (as showed in the picture below).
Last summer, a company that are JKW experts in the UK, excavated and treated these areas and have given a 10 year insurance to the property owner. The first 3 years will involve monitoring and further treatment if required (only in the affected areas though). My motivation to purchase this property is to be able to extend it to add more rooms and habitable space. However, one of the affected areas is about 5.4 m from the rear of the house. This was first found in 2013 but the company that tried to treat it then obviously was not successful. The JKW was about 0.5-1 m deep before treatment last year. I did a third party survey last month that found no traces of JKW. So it seems like the treatment has worked so far. However, if I need to build over or near the affected area (JKW01), I don't know the dangers I could face in the long term. Therefore, please make me aware of the liabilities that one could face if they had to build over or very near to the JKW affected areas even though the company has provided 10 yrs insurance. Note: The JKW treating company has some clause about building over or near the affected areas and I am trying to speak to them about it. Appreciate your advice in this regard.