If you are looking to buy or sell development land you should be aware that Japanese knotweed may reduce its value.

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The reduction in value is normally calculated based upon the cost of remediation plus the risk factor for the inherent risks associated with developing knotweed affected land.

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Typical risks include;

• Difficulty in securing external funding on land affected by knotweed

• Delays caused by planning objections from aggrieved neighbours

• Civil nuisance claims by adjoining owners for knotweed encroachment

• Increased costs and delays to construction

• Saleability of the developed land

• Litigation risk post sale

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Note: All of the above depend on site conditions including size of Knotweed infestation and typically apply to large infestations, as small infestations can generally be eradicated with minimum impact.

 

However, a good knotweed specialist can provide the key to maximising the development value by finding the most suited and cost-effective remediation method, and by helping to manage the inherent risks.

 

Herbicide is the most cost-effective control method. However, it takes repeated applications needing at least 3 -5 years to be fully effective. It’s an accepted method if ground is not to be disturbed, and some regrowth can be tolerated.

 

Total excavation of the root and rhizome system is a more robust method for development land, because it’s quicker and more effective. However, it’ may become expensive, especially if there is a large infestation on-site.

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Delays in construction programmes cost money. Unfortunately, Japanese knotweed remediation is not a precise science and in-experienced companies new to the invasive plant business can soon realize that things can go wrong. 

Common examples include encountering groundwater, ground contamination, below ground obstructions such as live services, all of which increase costs and can result in time delays.

For residential developments nearing completion, savvy solicitors acting for buyers will ask whether the site is or was previously affected by knotweed.

The developer will need to disclose the facts or risk future litigation. The buyer, backed by his solicitor and lender, may demand a copy of the site Management Plan including all associated reports. If these can’t be provided or are not compliant to current Best Practice (PCA - KCoP, 2018), and related legislation (S.I. 477, 2011) it’s likely the sale will stall.

A developer who does not disclose to a buyer that the land was affected by Japanese knotweed puts himself at unnecessary litigation risk. If Japanese knotweed emerges, the buyer as the new owner will be annoyed, and ask the developer to put things right. The new owner may also decide to claim for diminution in value.

If however the developer discloses that knotweed was present and can show there is a current eradication/control program in place. The developer in this instance should be better protected from any litigation risk.

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See: S.I. 477, 2011 under Section 49 -The section also provides for a defence (if it can be proven) that the accused took “all reasonable steps and exercised all due diligence to avoid committing the offence”.

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There are other alternatives, notably Soil Screening 

whereby infested soils are processed on site to remove the viable rhizomes and other visible contaminants.

 

The soils are re-used on site, thereby avoiding the excessive costs of off-site disposal and import of clean fill material. This method typically costs half that of disposal to landfill.

 

You might think that having commissioned a specialist to get the site remediated is the end of your knotweed problems. Unfortunately that might not be the case, as risks remain that need to be managed.

 

It’s not uncommon to find neighbours trying to frustrate development by objecting to planning. Whilst this tactic is unlikely to succeed, it may result in the imposition of a planning condition that will need to be discharged prior to commencement on site. Knotweed Control Ireland will be able to assist.

 

Japanese knotweed does not respect property boundaries. Encroachment, the spread from one parcel of land to another, is common. Aggrieved neighbours are increasingly resorting to litigation to resolve such issues, so it is vital that action is taken early to prevent or at least mitigate the risk to provide a strong defence to counter any expensive claim.

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