Japanese knotweed survey: cost, when you need one and what it involves
A Japanese knotweed survey confirms if the plant is present, how far it has spread and what risks it poses to your property. If knotweed is suspected during the house-buying process, a Japanese knotweed survey and management plan may be needed to satisfy lenders.
A Japanese knotweed survey is a specialist inspection that confirms whether knotweed is present, assesses how far it has spread and outlines the risks and treatment options.
KEY INFORMATION
Japanese knotweed surveys – at a glance
When you need one: If Japanese knotweed is flagged in a survey, mortgage valuation or is suspected on/near your property.
What it includes: Site inspection, risk assessment, mapping, a detailed report and recommended management plan (if needed).
Who carries it out: PCA-accredited Japanese knotweed specialists.
Impact on mortgages: A Japanese knotweed survey and management plan may be required by mortgage lenders, depending on RICS risk category.
Typical cost: From around £250 + VAT (varies by property and location).
What is a Japanese knotweed survey?
A Japanese knotweed survey is a detailed on-site inspection carried out by qualified specialists to determine whether Japanese knotweed (Fallopia japonica) is present on or near your property.
The survey will include:
An initial site assessment including a thorough visual inspection, mapping of the infestation areas, photography of identified specimens and inspection of neighbouring land.
Risk assessment including RICS risk category determination (see below), structural impact evaluation, spread potential calculation and mortgage and insurance implications and analysis.
Document preparation including a detailed report with photographic evidence, site map with infestation boundaries, treatment recommendation with a timeline and costs.
There are a number of reasons why you may need a Japanese knotweed survey. Here are the most common reasons.
1. Japanese knotweed is flagged in a mortgage valuation
When you’re getting a mortgage, the lender will require a mortgage valuation. If the surveyor flags Japanese knotweed, you may need a Japanese knotweed survey carried out before the lender agrees to lend.
In previous years, if Japanese knotweed was flagged, that would be enough for some lenders to decline a mortgage application. However, this position has evolved and lenders are now generally more open to lending in many cases.
2. Buying a house with suspected Japanese knotweed
If you’re buying a house, the presence of Japanese knotweed may be flagged on the house survey you commission and you may want a Japanese knotweed survey to get more information.
Whether it’s the buyer or the seller who pays for this will be up for negotiation. Find more information in our guide to Buying a house with Japanese Knotweed.
3. When selling a house with suspected Japanese knotweed
When you sell a house, you’ll be asked whether your property has Japanese knotweed in the TA6 property information form you complete about your property as part of the conveyancing process.
You’ll need to answer yes, no, or don’t know. If yes, you will also be asked to give details of any management and treatment plan in place and supply copies of any insurance policy you have.
If you know your property has Japanese knotweed, you must declare it. If you knowingly misrepresent any answers on the TA6 form or in replies to further enquiries and the buyer relies on that information when buying the property, the buyer can sue.
Getting a Japanese knotweed survey will clarify whether or not it’s present.
4. Japanese knotweed is in a neighbour’s garden
If you spot or suspect Japanese knotweed in a neighbour’s garden, you may consider getting a Japanese knotweed survey to determine whether the rhizomes have already crossed your boundary.
Getting a survey can also provide evidence for future legal action if you’re planning to pursue a private nuisance claim.
RICS has a sliding scale from category A to D when it comes to the severity of Japanese knotweed and this broadly fits how mortgage lenders view a Japanese knotweed problem. These categories are:
Management category A:Action. This is described as ‘significant impact, action required. Seek advice from remediation specialist on appropriate action. Recommend mortgage retention pending specialist report’.
Management category B: Action. This is classified as ‘potentially significant impact, action required. Seek advice from remediation specialist on appropriate action. Recommend mortgage retention pending specialist report’
Management category C: Manage. Described as ‘low impact, no action and no mortgage retention required for lending purposes.’
Management category D: Report. If Japanese knotweed is visible on adjoining land within 3m of the boundary. Described as limited impact. ‘No action and no mortgage retention required for lending purposes except in exceptional circumstances’. However, if there are concerns about the scale of an off-site infestation that may possibly affect the future value and saleability, this will be reported as a category D, even if it’s not within 3m of the boundary.
Some lenders are happy to lend on category C and D properties, but if it’s a category A or B property they may require a specialist report and the provision of an insurance-backed treatment plan. But there is no industry-wide standard when it comes to Japanese knotweed and each lender has its own lending criteria.
What happens if you don’t get a Japanese knotweed survey?
If Japanese knotweed is suspected but you don’t get a specialist survey, the consequences may be:
Mortgage delays or refusal: If Japanese knotweed is flagged in a mortgage valuation, lenders may delay or refuse your mortgage application until the risk is properly assessed.
Higher costs later on: Without a survey, the extent of the infestation may be unclear and treatment may become more complex and expensive over time.
What does a Japanese knotweed survey report include?
Your Japanese knotweed survey report should include:
Confirmation of whether Japanese knotweed is present.
Mapping of the infestation. The PCA recommends such plans show not just the Japanese knotweed visible, but indicate the likely and ‘worst-case’ spread of the rhizome network in the soil too.
Evaluation of risks to property, boundaries, and drainage systems.
Recommended treatment plan suitable for your infestation.
If your mortgage lender requires a risk assessment, this should be provided.
Who carries out a Japanese knotweed survey?
Japanese knotweed surveys are carried out by specialist surveyors. Make sure you use a Property Care Association-registered specialist because it provides the industry-standard accreditation, technical guidance, and professional, guaranteed treatment plans required to satisfy mortgage lenders.
Getting a Japanese knotweed survey – Step-by-step process
Find a PCA-accredited Japanese knotweed surveyor near you by using our handy tool.
Initial consultation. Discuss your concerns with the surveyor including any visible signs before arranging a visit.
On-site survey. A qualified specialist will carry out a full site assessment.
Risk evaluation. Your Japanese knotweed surveyor will assess the proximity to structures and potential damage risks, in line with RICS 2022 knotweed risk categories.
Report & recommendations. You’ll get a comprehensive Japanese knotweed survey report covering the surveyor’s findings and recommended management plan, such as herbicide treatment, excavation, or containment.
If Japanese knotweed is found in your survey, your options to manage or remove it will be outlined to you. These may include:
Management by herbicide spray
A control program and subsequent management plan using herbicide spray is often the most common and cost-effective approach which causes the least disruption.
Japanese knotweed rhizomes in the soil may not be eradicated and there remains a residual risk of re-growth. However, this risk can be off-set by an insurance-backed guarantee, says the Property Care Association.
Management through excavation and burial
This approach to Japanese knotweed management is to remove the plant and its extensive rhizome network from the soil completely, although this can be more costly and disruptive.
In some cases, a combination of both these approaches will be recommended.
Costs can vary depending on the property type and location.
How long does a Japanese knotweed survey take?
Japanese knotweed surveys can take around an hour, but the exact time will depend on factors including the size of the area surveyed.
You’ll be provided with a report following the inspection, it’s advisable to ask how long it is likely to take to get this before you commission your surveyor.
A Japanese knotweed survey is usually quick and straightforward and may take around an hour, depending on the size of the property and how accessible the affected area is. You’ll typically receive the written report within a few days.
Is a Japanese knotweed survey legally required?
A Japanese knotweed survey isn’t a legal requirement in itself. However, sellers must declare known knotweed on the TA6 property information form they fill in during the conveyancing process.
Will a Japanese knotweed survey affect my property value?
The survey itself doesn’t reduce your property’s value, but its findings can. If Japanese knotweed is confirmed, it may affect how much buyers are willing to pay. That said, having a professional report and a management plan in place may reassure buyers and lenders.
Do I need a survey if Japanese knotweed is in a neighbour’s garden?
You might. If Japanese knotweed is close to your boundary, especially within a few metres, it may raise concerns for buyers and mortgage lenders. A survey can assess the risk of it spreading onto your property and help determine whether any action is needed.
Do mortgage lenders always require a Japanese knotweed survey?
Not necessarily, however they may do if Japanese knotweed is flagged in a mortgage valuation, depending on the severity of the infestation.
What’s the difference between a knotweed survey and a management plan?
A survey identifies whether Japanese knotweed is present and assesses the level of risk. A management plan sets out how it will be controlled or treated over time. If Japanese knotweed is found, mortgage lenders may require both a survey report and a treatment plan with an insurance-backed guarantee.
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