We are worried about our neighbour’s Japanese Knotweed plant spreading

Invasive species will spread through walls, drains and foundations and can very quickly become a major infestation

 Japanese knotweed: a  most invasive plant. Photograph: PA

Japanese knotweed: a most invasive plant. Photograph: PA


We live in a city centre terraced house with a small back yard and on one of our boundaries our neighbour’s Japanese Knotweed plant is stretching the entire width of our garden. The plant is adjacent to our boundary wall and the plant’s foliage is hanging into our yard. We worry about the effects of this on the structure of our house as we have read that the roots can travel rapidly sideways and underground, with the ability to break through concrete as it grows. Our house is only about 10 feet from this plant and we are considering doing some house renovations and building a small extension. We have not talked to the owner of the neighbouring house yet as their house is rented out at the moment. We only recently became aware that this plant is definitely Japanese Knotweed. What can we do if the owner is not willing to eradicate the plant? Is this very dangerous to our house structure? Thoughts or advice please?

Having correctly identified that you have Japanese Knotweed nearby, then you are right to be concerned, as it is an invasive species that will spread through walls, drains and foundations. It’s vigorous root structure can spread into the ground by up to four metres from visible stems. It can very quickly become a major infestation, spreading even further and causing extensive and increasingly expensive damage.

Eradication of the species can therefore be very costly, particularly if its rapid spread remains unchecked. The most common treatment is the use of the relevant herbicide by a specialist company working to an agreed management plan over a set period of time. Don’t be tempted to cut or trim the Japanese Knotweed yourself as small fragments contaminate and spread easily and these will grow into full plants even months afterwards. Also soil removed within four metres of stems must be taken to an approved facility for treatment as it is considered hazardous waste.

Legal regulations

As quickly as possible, notify your neighbour to seek expert help to deal with this plant. Inform the owner of the situation, noting that if they are unwilling to co-operate there are legal avenues available that you might take to deal with this problem, eg: Regulations 49 and 50 of the European Communities (Birds and Natural Habitats); and Regulation 2011 which make it an offence to allow the dispersal of Japanese Knotweed. Crossing a boundary – which it will – certainly classifies as “dispersal” or escape and they will be liable for costs.

The Dublin Corporation Act 1890 in Dublin or the Land and Conveyancing Law Reform Act 2009 outside Dublin also apply. These Acts don’t make provisions for serving notice but the procedure under the 1890 Act is very succinctly described and allows you to “perform any other necessary works incident to the connexion of a party structure with the premises adjoining thereto”.

The eradication of the plant is necessary for the prevention of structural damage and should be done quickly, but, if a legal route is needed then you must serve the neighbour with three months’ notice in writing, stating the nature of the proposed work and the time at which it is proposed to carry out the work and informing the neighbour that they must respond within 14 days.

In this case, the neighbour is the owner, not the tenant. Legally, there are specific procedures to be applied and your solicitor is best placed to advise on the steps to be taken. If needed, then ultimately you can seek a court order to summons the owner.

Logging the presence of this invasive species on the database of the National Biodiversity Data Centre: biodiversityireland.ie will assist your case.

The Society of Chartered Surveyors Ireland has a guidance document for their members and your local Chartered Building Surveyor can assist.

Fergus Merriman is a Chartered Building Surveyor and member of the Society of Chartered Surveyors Ireland scsi.ie