Mortgages And Dangerous Japanese Knotweed

Mortgages Japanese Knotweed

Mortgages can be tricky, so can identifying Japanese Knotweed (JKW) if you’d like some help you can check out our post on identifying it here or if you’re still not sure you contact us and we’d be happy to assist.

Why do Mortgages Lenders have a Problem Japanese Knotweed?

Japanese knotweed is renowned for being able to find its way through cracks even in materials most plants could never grow through, they can break open existing cracks in foundations, brick walls, and damage sewage and drainage works. Which can all be very costly to fix or repair, this is why JKW on your property can be detrimental to the value of your property, on average knocking 15% off the value but in some cases this is a lot more and is dependant on the severity of the infestation.

As it is a plant it is constantly searching for a water source and sunlight, so naturally its vast root system will be attracted to places where there is water and moisture, so if it is on your property it can grow towards drains and crack through them if there is already an existing crack or gap to get to the water source. Same applies when it comes to sunlight it can find cracks in paving, concrete and tarmac and its shoot will push up through these cracks and as the shoot grows it will expand the already existing crack making it larger.

Unfortunately, in the winter even when JKW appears to be dead, it lies dormant underground waiting for the spring to return. Injecting or spraying with herbicides doesn’t always kill it, often it puts it into a state of dormancy so has the possibility to grow back very quickly after a few years, this is why insurance backed guarantees are need from a professional contractor.

The rhizome (root system) hardly decomposes if it is disturbed when dormant it could wake the plant and trigger its growth again, this is why excavation is the best method for removal although the material needs to be either disposed of safely as it is classified as controlled waste or buried deep underground and wrapped in a root membrane so it can not grow again. – These are both very costly procedures.

Mortgage lenders see this as a big problem, for example if you wanted to build an extension, conservatory or lay a patio, and you were to dig through the original rhizome system or disturb the soil around it, it can reawaken the plant. So many mortgage lenders believe it affects not just the existing structure but puts any future structures at risk also such as extensions. This is why they can be reluctant to lend on a property with it. This is why insurance backed treatment plans are needed to move forward when the property you’re selling has an infestation.

Japanese knotweed how it effects Mortgages

RICS Guidance

RICS (Royal Institute of Chartered Surveyors) published guidance on the severity of Japanese Knotweed infestations on or near to properties. Most lenders use this as the backbone for their research on a property regarding Japanese Knotweed and the level of risk present, so this is a good guide to use as a basis.

Category Description
4Japanese Knotweed is within 7 metres of a habitable space, conservatory and/or garage, either within the boundaries of this property or in a neighbouring property or space;


Japanese Knotweed is causing serious damage to outbuildings, associated structures, drains, paths, boundary walls and fences and so on. Further investigations by an appropriately qualified and/or experienced person are required.
3Although Japanese Knotweed is present within the boundaries of the property, it is more than 7 metres from a habitable space, conservatory, and/or garage. If there is damage to outbuildings, associated structures,
paths and boundary walls and fences, it is minor.

Further investigations by an appropriately qualified and/or experienced person are required.
2Japanese Knotweed was not seen within the boundaries of this property, but it was seen on a neighbouring
property or land. Here, it was within 7 metres of the boundary, but more than 7 metres away from habitable spaces, conservatory and/or garage of the subject property.
1Japanese Knotweed was not seen on this property, but it can be seen on a neighbouring property or land
where it was more than 7 metres away from the boundary.
Taken from the RICS document on Japanese Knotweed and residential properties.

Groundsure Japanese Knotweed Home Holiday Home Let Property 1030x772 2
Japanese Knotweed pushing it’s way through concrete paving.


Due to JKW being such a pain to get rid, how quickly it spreads and how it can cause damages to structures when left untreated, causing deduction in property value. So, you can probably understand why mortgage lenders can be uneasy when handing out mortgages, familiarising yourself with what Japanese Knotweed looks like is a helpful skill especially if you’re wanting to buy or sell. If you’re selling you need to make sure you answer the TA6 property form question on JKW correctly or you could end up having a claim against you.

If you aren’t sure how to identify Japanese Knotweed then you can get in touch with us and we will be happy to help assist you.

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