Japanese Knotweed Mortgages, RICS Categories and Lender Rules

What is a Japanese knotweed mortgage?

A Japanese knotweed mortgage is an ordinary residential or buy to let mortgage on a property where Japanese knotweed has been found on the land or within 3 metres of its boundary, with the lender's conditions for the knotweed written into the offer. Those conditions start from the RICS professional standard Japanese knotweed and residential property, which RICS valuers and surveyors have applied since 23 March 2022. The valuer or surveyor places the knotweed in a management category from A to D, and the category tells the lender what to ask for. At categories A and B the standard expects most lenders to require an inspection by a member of the Property Care Association (PCA) or the Invasive Non-Native Specialists Association (INNSA), and the works done under a management plan with an insurance-backed guarantee. At C and D it expects no works as a condition of the loan. Each lender still sets its own policy, so lenders can treat the same category differently, and some hold back part of the loan as a retention until the plan is evidenced.

The belief that knotweed within 7 metres of a house made it hard to mortgage comes from the RICS information paper of 2012. The 2022 standard replaced that test after research published in 2018 found no support for the idea that knotweed causes significant damage to built structures, and found that its rhizomes rarely extend more than 4 metres from the plants above ground (Fennell, Wade and Bacon, PeerJ, 2018). The standard now asks whether the knotweed is damaging a structure or affecting usable outdoor space, and whether it is on the property or next door.

Japanese knotweed (Reynoutria japonica, formerly Fallopia japonica) is a perennial introduced to the UK in the mid-19th century, when it was popular with landscapers. It grows tall, hollow, bamboo-like stems, often over 2 metres high in spring and summer, which die back to brown canes in winter. It spreads through underground stems called rhizomes, and gov.uk guidance says a new plant can grow from a piece of rhizome as small as 1cm. Soil or plant material contaminated with it may be classed as controlled waste. The RICS standard treats giant knotweed and the hybrid of the two in the same way.

Mortgage Lane arranges these mortgages for buyers whose survey or valuation has found knotweed, for owners remortgaging, for households with knotweed in a neighbour's garden, for landlords buying affected houses and HMOs and for auction and bridging purchases, and helps sellers whose buyer's lender has raised it. A mortgage to an individual on a home they or a close relative will live in is normally a regulated mortgage contract (Regulated Activities Order, article 61), arranged under the Financial Conduct Authority's MCOB rules. Most buy to let lending is assessed on the rent. In both cases the lender adds the knotweed evidence to its usual checks.

Japanese knotweed mortgage rates

The rate on a Japanese knotweed mortgage depends on the lender's product, the loan to value and the borrower, as on any other mortgage, and the knotweed is dealt with through the conditions in the offer. The knotweed's cost sits in the specialist survey, the management plan and guarantee, and any retention the lender holds back until the plan is evidenced. The valuation can matter as well. If the valuer reflects the knotweed in a lower figure, the loan to value rises and a different set of products may apply, as with any down valuation. Comparing lenders therefore means looking at how each one treats the management category, whether it makes retentions and when it wants the plan in place, alongside the rate, fees and term. A low rate is of little use if the lender's policy declines the category, or if the lender holds back more cash than the buyer has.

Survey or valuation found Japanese knotweed? Get in touch with the report, the management category and any plan or guarantee already in place. How each lender treats that category decides whether the offer carries a retention or waits for the plan.

Japanese knotweed mortgage criteria

Lenders start from the RICS management category, then read the specialist's report, the management plan and the guarantee. The table summarises what the RICS standard and the Law Society's notes on the TA6 form say, checked on 6 October 2026, and where lender policy can vary. The standard describes what most lenders are expected to do, and it accepts that each lender decides its own policy: some, for example, do not make retentions at all. None of the rows is a named lender's rule or a decision on an application.

Types of Japanese knotweed case, and how lenders treat each

The cases below differ in who found the knotweed and who pays for the plan, and some, such as auction purchases, also have to complete quickly.

Buying a house with Japanese knotweed

A buyer usually learns of knotweed from the seller's answers on the TA6 Property Information Form, from a home survey or from the lender's mortgage valuation. The steps from there are a specialist survey before exchange, which gives the management category, a quoted plan with an insurance-backed guarantee, and then agreement on who pays. At categories A and B the lender's offer is likely to be conditional on the plan, and the price negotiation depends on what the plan costs. Buying an affected home at a reduced price can work where the reduction covers the cost of management and the effect on resale, and the arithmetic below shows why a seller-funded plan can leave the buyer better off than a price cut of the same amount. Where the reduced price is below the lender's valuation, lenders that publish their approach lend on the lower of the price and the valuation, as our BMV mortgages page explains. First-time buyers follow the same sequence, and the schemes in the first-time buyer mortgage guide apply as usual.

Selling a house with Japanese knotweed

A seller who commissions the specialist survey and puts the management plan and guarantee in place before marketing has the documents the buyer's lender is likely to ask for ready at the offer stage, which can stop a sale stalling while a plan is arranged. The Law Society's notes on the TA6 (6th edition) say that a seller who is aware of a management plan should answer yes to question 8.6 and attach a copy, and should attach any survey report (Law Society: TA6 explanatory notes). Under the RICS standard a management plan should be transferable to later owners, so the plan, the treatment record and the guarantee should pass to the buyer on completion.

Remortgaging a property with Japanese knotweed

A remortgage valuation that records knotweed leads to the same questions as a purchase. An owner with a plan in progress, or with a completion certificate and a guarantee still in term, sends those to the lender. An owner without a plan can commission one, or look at a product transfer with the existing lender, which may not involve a new valuation, depending on the lender. That can suit an owner whose fixed rate ends before a plan can be arranged.

Japanese knotweed in a neighbour's garden

Knotweed seen on adjoining land within 3 metres of the boundary is management category D. The valuer reports it, and the RICS standard says lenders should not make treatment of a neighbour's land a condition of the mortgage, because the owner has no control over it. Only in exceptional circumstances does the standard expect a category D finding to become a mortgage condition. Knotweed seen more than 3 metres from the boundary is normally a note on the valuer's file, with no report to the lender. The owner's remedies against the neighbour are in the law section below.

Previously treated knotweed and existing guarantees

A property treated in the past is assessed on its paperwork. The RICS standard expects a management plan to include a treatment schedule and, at the end, a certificate confirming the plan is complete, including a 2-year period with no growth. It treats a properly evidenced plan or guarantee as satisfactory evidence, and where that evidence is missing it recommends a new inspection by a specialist. A lapsed guarantee, or one from a contractor that has stopped trading with no insurance behind it, may not count as satisfactory evidence. Treatment carried out by the owner may leave no record a lender can rely on. A seller in this position still answers the TA6 knotweed questions and attaches what they hold.

Flats and communal grounds

Knotweed in the communal grounds of a block is for whoever the lease makes responsible for the grounds, which the RICS standard notes may be the freeholder, a management company or an individual owner. The PCA's guidance for valuers says a management plan for shared ground names the ground owner or management company as the beneficiary, and flat owners can rely on it as if it were their own (PCA guidance for valuers and surveyors, December 2022). Where nobody responsible acts, every flat in the building can become harder to sell, as the RICS standard notes. Ask the managing agent for the block's plan before the offer. The rest of the case runs as on any mortgage for a leasehold flat.

Buy to let, HMO and portfolio purchases

Landlords buy affected property on the same knotweed evidence as owner-occupiers. For banks and building societies the Prudential Regulation Authority sets the buy to let underwriting standards (PRA SS13/16). That evidence is a condition of the offer, and the rental assessment follows the lender's usual buy to let rules on the expected rent, which those standards say should be verified by an independent valuer, an automated valuation model or evidence of an existing rental agreement. Houses in multiple occupation and multi-unit blocks follow the same route, and a portfolio landlord adding an affected property is assessed across the portfolio. The buy to let mortgage guide, the HMO mortgages guide and our portfolio mortgage page cover the rental tests.

Auction, bridging and development land

An auction purchase completes on a date fixed by the auction conditions, which may leave too little time to arrange a survey and plan before a term lender will release funds. A bridging loan can fill that gap where the bridging lender is prepared to lend while the plan is put in place, taking the knotweed and the plan's cost into its own assessment, with a term mortgage as the exit once the plan is running. According to the RICS standard, ground with knotweed cannot be developed without special precautions, typically removal and disposal of the contaminated soil by licensed operators, so a development lender looks at the excavation plan and its cost. Our bridging loans, bridging loans for auction and property development finance pages cover the structures.

Declined Japanese knotweed cases

A decline on an affected property can come from one of several causes: category A or B with no plan, a plan from a contractor outside the PCA or INNSA, treatment by the owner, a guarantee shorter than the lender's minimum or without insurance behind it, a lender whose policy declines the category, or a valuer's note with no specialist survey to follow it. Each points to its own fix, such as a compliant plan, a longer guarantee or a lender whose policy fits the category. A decline at the valuation stage is covered in mortgage declined after valuation, and the wider recovery steps on our declined mortgages page. Send us the decline reason with the survey, if there is one.

The RICS management categories

Since 23 March 2022, an RICS valuer or surveyor who finds Japanese knotweed at a residential property places it in one of four management categories, and lenders read the category in place of the old distance test. The standard's own imprint says it was first published in January 2022 as an RICS guidance note and reissued in October 2022 as a professional standard (RICS: Japanese knotweed and residential property). It replaced the 2012 RICS information paper, whose four risk categories used a distance of 7 metres from buildings and boundaries. The standard records that a 2019 report by the House of Commons Science and Technology Committee called the 7 metre rule a blunt instrument and asked for a more nuanced, evidence-based process, and that the 2018 research led to general agreement that 3 metres is a better measure of how far the rhizome typically spreads.

The valuer decides the category with a decision tree. Knotweed along a boundary or in a boundary hedge counts as on the property, and where knotweed is on both sides of the boundary, the highest on-site category applies. Damage means damage the knotweed has itself caused: the standard says knotweed growing through cracks that were already there has not necessarily caused them, and it cites the 2018 research as finding that knotweed cannot grow through intact concrete. Amenity space means open areas such as lawns, patios, paths, driveways and hardstandings. The standard covers residential property across the UK, including the single survey in a Scottish Home Report, and it presents the framework as guidance, so a valuer can use professional judgement where a case does not fit it.

The standard also changes the aim of treatment. It says eradication should not generally be the main objective, except before construction, and that effective control is usually more economical, with herbicide treatment suitable in many domestic gardens. Its recommendations for categories A and B are almost identical. RICS separates them to distinguish damage to a structure from loss of amenity, in the hope that lending policies will become more precise over time.

Japanese knotweed surveys and the mortgage report

Three kinds of inspection can find Japanese knotweed during a purchase, and the specialist's is the one that produces the report and plan a lender acts on. The lender's valuer records knotweed seen on or near the property and gives it a management category. An RICS home survey at level 1, 2 or 3 does the same for the buyer, in more detail at each level. Under the RICS standard, valuations and surveys are not substitutes for an inspection by a specialist remediation company, and where a client wants advice on whether knotweed is present or how to treat it, the surveyor should recommend a specialist from a recognised trade body. It names two, the PCA and INNSA, and both list their member firms. Those member lists are where to find a Japanese knotweed survey near you; the valuation and the home survey come with the purchase itself. The PCA also runs a qualification for specialist surveyors, the Certificated Surveyor in Japanese Knotweed (CSJK).

What a Japanese knotweed mortgage report contains

The RICS standard lists what a Japanese knotweed management plan should include: a description of the property with an accurate record of the infestation, a scaled plan with dimensions, full details of the contractor and the methods it will use, a treatment schedule updated as the work is done, and a certificate on completion. It adds that the plan should cover the whole property, including any parts the valuer or surveyor did not identify, should be transferable to later owners, and should carry a guarantee of at least 5 years after the remediation contract is complete, with insurance behind it in case the contractor becomes insolvent. The PCA's guidance for valuers says a qualified knotweed surveyor prepares the report and management plan with costs and, usually, the offer of a guarantee. That quotation is the figure the price negotiation works from.

When to survey, and what a knotweed survey costs

Knotweed is harder to see outside the growing season, after it has been cut down, or where earlier treatment has left dormant rhizome below ground, and the RICS standard accepts that a competent inspection can miss it in those cases. A survey commissioned by the seller before marketing has the report ready when a buyer's lender asks for it. A buyer who commissions one before exchange has the quotation in hand for the price negotiation. The fee is set by the contractor and depends on the property and the purpose of the report, so if a mortgage is involved, ask for a report written for a lender.

Management plans and insurance-backed guarantees

A Japanese knotweed management plan is the specialist's written programme for treating a mapped area of knotweed, and the insurance-backed guarantee keeps the promise to deal with regrowth valid if the contractor stops trading. The RICS standard expects the plan to reflect current law and the latest codes of practice, such as the PCA code of practice for the management of Japanese knotweed (November 2023) or the code of practice published by INNSA. At categories A and B it expects most lenders to want the works done under a plan, with the benefit of an insurance-backed guarantee. The government's guidance for England says not to treat knotweed yourself unless you have the skills and experience, and lists the PCA and INNSA as the trade bodies many specialist firms belong to (gov.uk: how to stop Japanese knotweed from spreading).

For residential property the RICS standard says there are usually two options, herbicide or excavation, and that plans may combine them. Herbicide suits many gardens because it is effective and economical, but it can leave dormant rhizome in the ground that regrows if the soil is disturbed later, for example by digging foundations, so the plan and its guarantee stay relevant for later owners. The PCA's code of practice says a plan that relies only on herbicide must include at least 2 years of monitoring after all evidence of growth has stopped, and that herbicide alone should not be recommended where the soil will be dug for development. It also says a vertical root barrier on its own is not a solution and has to be combined with herbicide treatment and monitoring.

The insurance-backed guarantee

The contractor's guarantee is a promise to come back and treat any regrowth in the treatment area during the guarantee period. The RICS standard expects at least 5 years from the end of the remediation contract, and the PCA's code of practice says guarantees most commonly cover 5 or 10 years. A separate insurance policy can sit behind the guarantee so that it stays valid if the original contractor ceases to trade, and the RICS standard calls the two together an insurance-backed guarantee. Under the PCA's code, the insurer issues that certificate only once the works are complete and the contractor has issued its completion certificate. The minimum term a lender accepts, and the evidence it wants while a plan is still running, are set by the lender.

Japanese knotweed insurance: guarantees, indemnity and buildings cover

The insurance-backed guarantee covers the treatment plan. A legal indemnity policy arranged through a conveyancer is a separate product, and whether it covers knotweed, and on what terms, depends on its wording. A lender whose offer asks for a management plan will look for the plan itself. Buildings insurance differs from policy to policy, and a policy may exclude both damage caused by knotweed and the cost of treating it, so check the wording before relying on it.

Japanese knotweed law, disclosure and claims

Having Japanese knotweed on your land is not an offence. The rules that do apply cover letting it spread and handling its waste, and a seller's answers about it carry legal weight on a sale.

The statutes

In England and Wales, section 14(2) of the Wildlife and Countryside Act 1981 makes it an offence to plant or otherwise cause to grow in the wild any plant listed in Part II of Schedule 9, and Japanese knotweed is on that list. In Scotland the same section, as amended, makes it an offence to plant or cause to grow any plant in the wild outside its native range. In Northern Ireland, article 15 of the Wildlife (Northern Ireland) Order 1985 creates the same offence for the plants in its own Schedule 9, which includes Japanese knotweed. In England, Wales and Scotland, soil or plant material contaminated with knotweed may be controlled waste under Part 2 of the Environmental Protection Act 1990, and section 34 puts a duty of care on those who deal with it. In England and Wales that means anyone who imports, produces, carries, keeps, treats or disposes of it, or controls it as a dealer or broker; the Scottish version of the section covers anyone who imports, produces, keeps or manages it, or controls it as a broker or dealer. In Northern Ireland the duty of care is in article 5 of the Waste and Contaminated Land (Northern Ireland) Order 1997. The gov.uk guidance for England says you do not legally have to remove knotweed from your land unless it is causing a nuisance, that you must stop it spreading off your property, and that you can be prosecuted for causing it to spread into the wild. Waste that leaves the site must go with a registered waste carrier to a landfill site or incinerator with the correct permit, and burying it on site needs at least a month's notice to the Environment Agency.

Community protection notices and fines

In England and Wales, a council or the police can serve a community protection notice under section 43 of the Anti-social Behaviour, Crime and Policing Act 2014 where someone's conduct is having a persistent or continuing detrimental effect on the quality of life of those in the locality and is unreasonable. A written warning must come first. Home Office guidance from 2014, cited in the RICS standard, described how the power could apply to a failure to control knotweed. Failing to comply without a reasonable excuse is an offence: the fine is up to level 4 on the standard scale (£2,500) for an individual, and unlimited for a body (section 48), and a fixed penalty of up to £100 can be offered instead (section 52). A homeowner cannot use this remedy directly, so someone with a problem next door would ask the council to act, as the RICS standard points out.

Disclosure when you sell

In England and Wales the seller completes the Law Society's TA6 Property Information Form. Its 6th edition replaced the 4th and 5th editions on 30 March 2026, and firms in the Law Society's Conveyancing Quality Scheme must use it on new transactions where they were instructed on or after that date (Law Society: TA6 6th edition). Question 8.6 asks about the presence of Japanese knotweed. The same question and question 8.7 then cover any survey and management plan, with copies to be attached. The Law Society's notes say a property is usually considered at risk if knotweed is growing on it or within 3 metres of its boundary, and that because rhizome can be in the soil with nothing visible above ground, many sellers answer not known. The RICS standard adds that knotweed has to be declared on the TA6 even after it has been treated, which is one reason the plan, the completion certificate and the guarantee are worth keeping. The seller's answers are statements the buyer relies on. Under section 2(1) of the Misrepresentation Act 1967, a buyer who entered the contract after a false statement and suffered a loss as a result can claim damages, unless the seller proves they had reasonable grounds to believe, and did believe up to the time of the contract, that it was true. In Scotland the seller provides a Home Report, and the RICS standard extends to the single survey within it.

Claims between neighbours

In Network Rail Infrastructure Ltd v Williams, decided on 3 July 2018, the Court of Appeal held that knotweed rhizomes encroaching from a neighbour's land are an actionable private nuisance, because they reduce the owner's ability to use and enjoy the land, even before any physical damage ([2018] EWCA Civ 1514). It rejected the trial judge's reasoning that a fall in value caused by knotweed nearby is by itself the kind of interference the tort covers, since nuisance protects the owner's use and enjoyment of land. It still upheld the damages awarded, which included a treatment package with an insurance-backed guarantee and the fall in value left after treatment. On 8 May 2024 the Supreme Court considered that loss again in Davies v Bridgend County Borough Council and allowed the council's appeal ([2024] UKSC 15). The knotweed had spread onto the claimant's land before the council's breach of duty began in 2013, and there was no evidence that the breach had added to the fall in value, so the remaining fall in value was not caused by the breach and no damages were awarded. Both cases apply the law of England and Wales, and Scotland and Northern Ireland have their own law of nuisance. Mortgage Lane arranges the finance and does not advise on claims, which are a matter for a solicitor.

How a Japanese knotweed mortgage is arranged

1. Identify and survey. Start from the valuer's note, the home survey or the TA6 answer, then a specialist survey by a PCA or INNSA member giving the management category, the plan and the guarantee quotation.
2. Plan, guarantee and who pays. Agree the management plan and the insurance-backed guarantee, and settle who pays: the seller before exchange, a price reduction, or the buyer, with or without a lender's retention. The arithmetic below compares the three routes.
3. Lender match, application and valuation. Place the case with a lender whose policy accepts the category on terms that suit the timetable, whether that means no retention, the plan in place before completion or a retention until the plan is evidenced. An agreement in principle can come first, though it is given before the lender has seen the property. The full application goes in with the survey and plan, and the lender's valuer reflects the category.
4. Offer conditions, completion and release. Where the category calls for it, the offer is conditional on the plan and guarantee. Completion follows once the condition is met, and any retention is released on the evidence the lender specified. Keep the plan, the guarantee and the completion certificate for your own sale.

The knotweed arithmetic: cost, retention and price

Three things decide the money on a knotweed purchase: what the plan costs, how the lender treats that cost and who pays it. In the illustration below, the choice of who pays changes the buyer's cash at completion by up to twice the plan's cost.

Step 1. What the plan costs, and why

The specialist's quotation fixes the cost, and the method and the extent of the knotweed drive it. Herbicide over several growing seasons is the economical route and the slow one: the gov.uk guidance says it usually takes at least 3 years to treat knotweed this way, and the RICS standard says a herbicide plan needs a minimum of 4 years of treatment and monitoring before a completion certificate can be issued. Excavation aims to remove the knotweed straight away, with monitoring afterwards, but the volume of soil makes it disruptive and costly. The RICS standard says the dig typically takes in 2 to 3 metres beyond the visible edge of the stand and goes 1 to 2 metres down. On that basis a 2 metre by 2 metre stand might need a 6 metre by 6 metre area dug out, as much as 72 cubic metres of soil, and the waste charges for excavation, transport and landfill tax come on top. The PCA's guidance for valuers names access, waste handling and disposal charges among the things that move an excavation price. It also gives indicative cost ranges for typical cases, which RICS describes as an aid to a valuer's first assessment before a specialist has quoted. The £5,000 plan cost used below is illustrative and is not a market rate.

Step 2. How the lender treats the cost

The figures take an illustrative £250,000 purchase at 85% loan to value, with a management plan and guarantee quoted at an illustrative £5,000, and assume the valuation equals the price.

Illustrative arithmetic on hypothetical figures. The plan cost and the retention stand in for the actual quote and the lender's own policy. Not an offer of finance.

Step 3. Who pays, and why the route matters

The table below shows the same £5,000 plan paid for in three ways. In route A the seller pays for the plan before exchange. In route B the price comes down by the plan's cost and the buyer pays for it. In route C the price stays the same, the buyer pays for the plan and the lender holds back a retention equal to its cost until the plan is evidenced. The valuation is assumed to equal the price paid in each route.

Routes A and B leave the seller with the same £245,000, but under route B the buyer needs £4,250 more cash. A £5,000 price reduction lowers the 15% deposit by only £750, because the other £4,250 of the reduction comes off the loan, and the buyer still pays the full £5,000 for the plan. A seller-funded plan keeps the full loan and gets treatment under way before exchange, which makes it worth asking the seller for first. Route C needs the most cash at completion, £47,500, because the buyer funds both the plan and the £5,000 the lender has retained until it is released. After the release the buyer's outlay comes down to £42,500. Route C suits a seller who will not engage and a buyer with the cash, provided the lender's retention and release terms are known before the offer. The calculator below runs the same arithmetic on your own figures.

Step 4. The effect on value

The RICS standard tells valuers not to reflect only the cost of remediation, and not to apply a standard percentage reduction without a justifiable evidence base. It points them to five factors, added to the cost of the works: the effect on the market before remediation, restrictions on using the property, the effect during remediation, knotweed on adjoining land, and the effect on future saleability once remediation is finished, when some stigma may remain but should lessen over time. Its notes on the categories expect value to be likely affected at A, possibly affected at B and usually only modestly affected at C, with a limited effect at D unless severe knotweed next door makes costly defensive measures desirable. A buyer with the quotation and the category in hand can negotiate from those figures.

What decides the case

The survey fixes the category. Buyer and seller decide who pays and in what order, and the choice of lender decides how the category, the retention and the timing are treated. In practice that puts the specialist survey before the price is agreed, the plan before the application, and the lender's retention terms before the offer.

The other property checks lenders make, such as the type of construction, are covered on our non-standard construction mortgages page, and a decline that follows a survey in mortgage declined after survey.