Japanese KnotWeed

Japanese knotweed (Fallopia japonica): An analysis of capacity to cause structural damage (compared to other plants) and typical rhizome extension” which has resulted in some reports suggesting that Japanese knotweed’s capacity to cause damage to buildings is a myth.

Experienced specialists in the field of Japanese knotweed have seen many a case of damage to buildings on various levels.

Japanese knotweed is unlikely to cause significant structural damage to buildings indirectly by subsidence, or by collapse, as in a tree-fall. Japanese knotweed does however cause damage, both by its above ground canopy exerting pressure on adjacent walls/fences, but also by its expanding network of underground rhizomes and roots, and, for mature stands, its crown. The underground structure of this plant can grow far and wide and can have a massive impact on underground structures such as foundations, but also waste and water pipes, electricity cables and other linked matters.

In our experience the distance that the rhizome may be found from the visible plant (above ground) is on average 2-3m but could be more or less depending on site conditions. Rhizome tends to reduce in diameter with distance from the crown. However, these rhizomes do have the ability to exploit weaknesses in built structures and will then expand exerting pressure on the element to cause damage. The damage will range from cosmetic to minor and if left unchecked, can lead to significant damage which could prove extremely costly to repair. We agree that damage that undermines the structural stability of a property is rare and would only occur where the problem has been ignored or not noticed and as a result been exacerbated.

We have seen many cases of rhizomes growing into underground drains. They not only block the drain but eventually expand and crack them, meaning that the drain run needs to be replaced.

We’ve seen Japanese Knotweed growing within cavity walls of buildings, with canes growing out through air bricks to find sunlight. The woody mass of rhizome in the cavity pushes the inner and outer skins of the wall apart resulting in an extremely costly repair.

The most extraordinary case we have heard of is knotweed growing out of a chimney pot on a 2 storey building. Japanese Knotweed was growing within the building’s façade, a solid old stone wall. It had then grown into the chimney flue. When inspected from above it could be seen that the entire flue was blocked with dense woody mature rhizome and crown material. The chimney and wall had to be taken down to remove the rhizome material and the wall had to be rebuilt. If that is not significant structural damage tell me what is!

The study states that knotweed does not grow through concrete, which we would partly agree with. However, Knotweed is very successful at finding weaknesses in concrete and exploiting any cracks. It can then cause damage. We’ve seen it growing through a concrete floor at the intersection of a service duct. We’ve also seen it growing up behind skirting boards where a new concrete floor for an extension abutted the original floor.

There are many cases of it growing up through and lifting asphalt. Whilst there are many plants that may be able to do same, it clearly can cause damage, an unwelcome sight on a newly laid driveway.

We have seen reports in newspapers claiming that a property needed to be demolished as knotweed was growing under it. This is quite a claim, but in our view to say that Japanese knotweed does not cause significant damage to buildings is also not true. As usual the truth lies between these two extremes of views. Each case is therefore assessed on its own individual circumstances and only with an expert on site can we truly know the route and location and subsequent damage effects of each growth.

Due to the fast growing invasive and damaging effects of Japanese knotweed we believe that mortgage lenders are right to restrict lending criteria on affected properties. Their policies have probably resulted in the largest deployment of resources to eradicate the plant, described by the Environment Agency as “indisputably the UK’s most aggressive and destructive weed” – that is surely a good thing, and is more than any government body has been able to achieve to protect consumers from the knotweed menace.

Property managers play a vital role in ensuring compliance with these requirements, safeguarding property values, and contributing to the ongoing battle against Japanese knotweed.

If you’re interested in pursuing a career as a property manager, you can explore job opportunities on Jooble at this link: https://uk.jooble.org/jobs-property-manager/France

Japanese Knotweed grows quickly and its strong roots can create a destructive underground network undermining buildings and foundations, and potentially causing thousands of pounds of damage.

How quickly does knotweed spread?

Japanese Knotweed can grow up to ten cm per day, with roots growing out in a seven-metre radius, meaning it can quickly spread from one garden to another, infesting whole areas.

The cost of letting Japanese Knotweed spread

Homeowners whose properties become infected with Japanese Knotweed due to negligence by neighbours who let the weed spread will now be able to claim damages. This follows the case of Williams and Waistell v Network Rail. The two neighbours in Maesteg, South Wales, were awarded damages after the rail company failed to prevent the spread of the Japanese Knotweed on to their land.

Stephen Williams and Robin Waistell owned adjoining bungalows backing on to Network Rail property. Japanese Knotweed had been present on the rail company’s land for over fifty years, and the two had first complained about it in 2013.

In 2017, the pair won their case and were each awarded £4,320 to treat the Japanese Knotweed, plus a further sum of £10,000 to compensate them for the fall in property value. Payment was withheld pending an appeal by Network Rail, which was resolved and saw the two men both receiving their money.

The Appeal Court said that the men were entitled to the full payment, although the judgment said that the £10,000 payments were to compensate them the inability to enjoy their property rather than the loss of potential value.

What happens if you let Japanese Knotweed spread?

If you have Japanese Knotweed on your property, you need to get rid of it and prevent it spreading. Allowing Japanese Knotweed to spread from your garden into the wild contravenes the Wildlife and Countryside Act 1981. If you allow the plant to spread to a neighbour’s garden or to private land in general, you may be liable for removal costs, damages, court costs and possible land yourself with an ASBO too.

How do you get rid of Japanese Knotweed?

Excavation is one means of eradicating Japanese Knotweed from your land. It is the fastest means to rid yourself of the weed and a legal requirement if the land is intended for development in the future. However, even the tiniest trace of rhizome left behind in the soil can regrow, for this reason the best solution is to use a professional Japanese Knotweed company, which will provide you with a certificate guaranteeing the weed has been eradicated.

Spray herbicides is the best solution for large infestations in areas that are not ecologically sensitive. The herbicide is applied to the leaves and absorbed down into the rhizome. This treatment normally takes 24 months.

Stem injection is used when you don’t want to affect other nearby plants whilst eliminating Japanese Knotweed. By injecting the herbicide directly into the stem it is absorbed throughout the rhizome deep into the plant’s root system.

How does Japanese Knotweed spread?

Pollination – Although Japanese Knotweed does flower and produce seeds, it is very rare for it to spread in this way.

Stems – New Japanese Knotweed plants can grow from stem fragments. This often happens when machines like strimmers are used in proximity to the weed.

Crown – Even after drying or composting, the crown is able to survive and will rapidly grow new canes when it comes into contact with soil or water again.

Rhizome – Pieces of the underground stem can regrow from as little as a 0.7 gram fragment. Breaking up the rhizome stimulates new growth at an accelerated rate.

Is Japanese knotweed a notifiable plant?

Japanese Knotweed is a garden pest and it is the responsibility of the landowner to manage it. While it is an invasive plant and it is advisable to take action quickly to prevent it spreading, there is no statutory requirement to control/eradicate or even report its presence.

It is, however, an offence, under the Wildlife and Countryside Act 1981, to plant or cause Japanese Knotweed to grow in the wild. This can be enforced by both the police and local authorities, and you may face a fine of £5,000 or even a prison sentence.

Identifying Japanese Knotweed

If you do suspect an infestation of Japanese Knotweed on your or your neighbour’s property, you can send us a photo for a free, no-obligation check. To talk to one of our Environment Officers about Japanese Knotweed or any of our services you can get in touch with Japanese Knotweed Agency on freephone 03335 777 888

Does Japanese knotweed cause property damage?

The consequences of letting Japanese Knotweed spread Why Japanese Knotweed is a problem?