Should I be worried about Knotweed?

Your queries answered

The lime-green leaves of the knotweed plant: eradication of this invasive species can be challenging and expensive. Photograph: Thinkstock

The lime-green leaves of the knotweed plant: eradication of this invasive species can be challenging and expensive. Photograph: Thinkstock


Q I moved into my three-bed semi-detached house five years ago. My (unattached) neighbour just told me that they have Knotweed and my property could be affected too. I don’t have a clue what this means or if it’s serious. What should I do?

A Knotweed is an invasive plant species introduced to Europe in the late 19th century initially as a garden plant. Their spread has escalated because they have no natural predators outside their native habitats. In Ireland there are four regulated types of Knotweed.

It should be noted that it is an offence under the Wildlife Act 1976 for a person to plant, disperse, allow or cause to disperse, spread or cause to grow any prohibited species. The four regulated Knotweed species are included on this list.

You indicate that the plant has been brought to your attention by your neighbour who believes that it is located within their property. You should initially seek professional advice from a Chartered Building Surveyor or gardening expert to confirm identification of the plant and implement a management plan in conjunction with your neighbour.

Identification of the plant in early spring is noted due to the red and purple shoots that grow from the ground. By mid-summer it can be distinguished from other plants by its tall hollow bamboo-like canes that are covered with purple speckles.

The lime green leaves are arranged in a zig-zag pattern along the canes and the leaves are shield shaped with a flat base and pointed tip. In winter the leaves will die back leaving a visible and distinct cane that can be identified.

The Society of Chartered Surveyors Ireland has produced an information paper to advise how best to manage and assess the risk of Knotweed. The assessment of Knotweed has been split into four separate categories which will allow a suitable management plan to be put in place. It is important that any management plan should cover the entire site and not just the visibly affected parts.

Once Knotweed has established itself on a site, it can cause damage to property (drains, paths and buildings). Its eradication/control can be challenging and expensive. The following advice should also be adhered to; you should not strim the Knotweed as this will create tiny pieces of the plant which will then spread and grow into new plants. You should also not attempt to dig up the plant, cut it back or attempt to compost the cuttings.

In terms of effective treatment of the plant there are a number of options available. These include;

– Excavating infested soil and removing it to an appropriately licensed waste management facility. All disposal in this instance should be carried out in accordance with the Waste Management Act.

– Knotweed can be excavated and then buried on site but it must be covered with five meters or more of overburden soil and a specialist root barrier membrane installed to fully or partial encapsulate the Knotweed-bound soil.

– A root barrier membrane can also be used to encapsulate Knotweed where space does not allow burial.

– Chemical control with a special herbicide. Treatment with herbicides is the most commonly used and cost-effective method, although it can take two to four years to achieve acceptable control and/or eradication.

Due to the nature of Knotweed it can spread quite rapidly and therefore action on its removal and reduction in spread would need to be carried out by both parties. You should not ignore the situation as a small amount of Knotweed plant can quickly become a major infestation.

Andrew Ramsey is a Chartered Building Surveyor and Chartered Project Management Surveyor and is chairman of the Building surveying Professional Group Committee of the Society of Chartered Surveyors Ireland (SCSI)


Q I have recently completed renovation work in my bathroom. As part of the renovation, I asked an electrician to install an extractor fan in the bathroom. Upon an initial inspection, he stated that he would drill through the wall to the outside to install the fan. When work began to install the fan, the electrician changed his mind and said that he would drill a hole into the ceiling and up into the loft. Not knowing any better, I allowed him to continue and now I have bad condensation on the loft felt. I suspect that both are connected. If not what is the cause and what could I do to remedy it?

A The point of a bathroom extractor is to expel the moisture laden air from your bathroom. There is always moisture in the air in the form of water vapour, although usually it cannot be seen. However, there is a limit to how much vapour the air can hold at any particular temperature; the higher the temperature the more vapour the air can hold. Therefore when warm moist air comes into contact with a cold surface and is cooled it can no longer hold so much vapour and the excess condenses as liquid water on the cold surfaces.

This is what is happening in your roof void. As soon as the air passes through the insulated ceiling of your loft it hits colder air, when it hits the underside of the roof it condenses. If the builder did not wish to go through the wall it is a requirement for this moisture rich air to be ducted out through the pitched roof to the exterior. This could have been done through a purpose made insulation wrapped flexible duct connected to a roof vent tile.

In the past builders have used standard flexible ducts, like those used at the rear of tumble driers. As these are not insulated the moisture rich air condenses before it can get to the air and drops back down. It is an easier option to go through the wall than the roof void if both are done correctly.

Kevin Hollingsworth is a Chartered Building Surveyor and a member of the SCSI.


Q Earlier this year the fence separating my house from my neighbour’s was blown down during a particularly windy night. To be honest it was regularly falling down before that and we always made some attempt to get it upright between us. On the last occasion however, my neighbours dogs came into my garden, trampled all over my plants and generally ran amok. My neighbour and I have fallen out over this. My neighbour has since installed a brand new fence but not in the original place which was inside their boundary line. Now I’m positive it’s on my property and my garden, which was small to begin with, is even smaller now. What am I to do?


A It is unfortunate that you and your neighbour have fallen out over dogs. It appears that you were aware that the fence was not fit for purpose and that “getting it upright” was not a permanent solution. It also appears that you accepted joint responsibility and regarded it as a party fence, despite the fact that, as you suggest, it was on your neighbour’s side of the boundary. You do not say what materials the new fence is constructed with or what distance/area is involved. A boundary fence constructed on the legal boundary would be a party fence and any work carried out on it should be by agreement. Locating the new fence on your side is an encroachment.

You should first ascertain the location of the legal boundary from your deeds. You may need the assistance of a Chartered Geomatics Surveyor to do this. You should then compare the location of the new fence with the legal boundary location and the location of the original fence and assess the extent of the encroachment based on whichever of the latter two locations is closer to your side. This exercise will enable you to put the encroachment issue, if any, in context. If, for instance, the encroachment is minor and the new fence is of a substantial construction such as a concrete block wall, it may be advisable to just accept it, as demolition and reconstruction would be expensive and likely to seriously escalate difficulties with your neighbour. If the encroachment proves to be significant or the fence is of a lighter or transferable material, you should explain the situation in as friendly a manner as possible, and suggest that, if necessary, your surveyor will clarify the situation. Consider offering to do the work involved in cooperation with your neighbour. Whatever course of action you take it is of paramount importance that you try to repair your relationship with your neighbour. It may be the only means towards rectifying the fence location. The alternative may involve litigation which should be a last resort and only considered in serious circumstances.

Patrick Shine is a chartered geomatics surveyor, a chartered civil engineer and a member of the SCSI