Can you get a mortgage on a house with Japanese knotweed?

Yes, mortgages are possible on properties with Japanese knotweed. If it's over 7 metres from the property, most lenders proceed normally. Closer infestations require a professional treatment plan with an insurance-backed guarantee (usually 10 years). Some specialist lenders accept properties with knotweed under active treatment.

Can you get a mortgage on a house with Japanese knotweed?

Yes, but it depends on severity and treatment. If knotweed is over 7 metres away with no structural risk, most lenders proceed normally. Closer infestations need a professional treatment plan with insurance-backed guarantee. Some specialist lenders accept properties with active knotweed under treatment.

How do I identify Japanese knotweed?

Look for: shield-shaped leaves up to 20cm, hollow bamboo-like stems with purple speckles, zig-zag stem growth, heights up to 3m in summer, creamy white flowers in August-September. In winter, dead brown canes remain standing.

Is it illegal to have Japanese knotweed in your garden?

Having Japanese knotweed is not illegal. However, allowing it to spread to neighbouring properties can lead to legal action. It's an offence under the Wildlife and Countryside Act 1981 to plant or cause it to grow in the wild. You must dispose of it as controlled waste.

How much does Japanese knotweed treatment cost?

Herbicide treatment: £2,000-£5,000 over 3-5 years. Excavation: £10,000-£50,000+. Root barriers: £5,000-£15,000. Insurance-backed guarantees typically add £1,000-£2,000. Costs depend on infestation size and property access.

Do I have to declare Japanese knotweed when selling?

Yes. The TA6 property information form specifically asks about Japanese knotweed. Failing to disclose can lead to legal action from buyers for misrepresentation. You must declare if you know it's present or has been treated.

Can Japanese knotweed damage my house?

Japanese knotweed exploits existing weaknesses like cracks in walls, drains, and paving. It rarely penetrates sound structures but can widen cracks and block drains. The main concern for lenders is property devaluation and spread to neighbours.

Quick Answer

How Does Japanese Knotweed Affect Getting a Mortgage?

Last reviewed: December 2025

Reviewed by Jay Sabine – CeMAP Qualified – 29 years experience

Mortgages are available for properties with Japanese knotweed, but requirements depend on proximity. Over 7m away: standard lending. Within 7m: treatment plan needed. Affecting the property: specialist lender + insurance-backed guarantee required.

Japanese knotweed is the UK's most invasive plant and a major concern for mortgage lenders. Surveyors use RICS categories to assess risk. The key factors are: how close it is to the property, whether it's under treatment, and if there's an insurance-backed guarantee. With proper documentation, many properties are mortgageable.

Key Points

1Over 7m away = usually no issue
2Within 7m = treatment plan required
3Affecting property = specialist lender needed
4Insurance-backed guarantee essential
5Treatment takes 3-5 years typically
6Must declare when selling

Eligibility Criteria

Professional survey and categorisation
Treatment plan from PCA member
Insurance-backed guarantee (10+ years)
Evidence treatment is progressing

Typical Timeframe

Herbicide treatment typically takes 3-5 years for full eradication. Insurance-backed guarantees are usually 10 years. Excavation is faster but more expensive.

Next Steps

1Get a professional knotweed survey
2Obtain treatment quotes from PCA members
3Request insurance-backed guarantee
4Speak to a specialist mortgage broker
5Consider price negotiation

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For more detailed information about this topic, visit our comprehensive guide:

Mortgages

Jay Sabine

CeMAP Qualified

29 Years Experience

Content reviewed: 13 January 2026

How to Identify Japanese Knotweed

Heart or shield-shaped leaves up to 20cm

Hollow bamboo-like stems with purple speckles

Zig-zag growth pattern on stems

Creamy white flower clusters in late summer

Grows up to 3 metres tall in summer

Dead brown canes remain through winter

RICS Risk Categories & Mortgage Impact

Category	Mortgage Impact	Action Required
Category 4 (over 7m away)	Usually no issue for mortgage	Standard mortgage likely available
Category 3 (within 7m)	Some lenders may decline	Treatment plan usually required
Category 2 (within 3m)	Many lenders will decline	Professional treatment essential
Category 1 (affecting property)	Most lenders will decline	Full treatment + insurance-backed guarantee

Treatment Options & Costs

Herbicide treatment

Most common, requires patience

Duration:3-5 years

Cost:£2,000-£5,000

Excavation and removal

Fast but expensive, soil is controlled waste

Duration:Days to weeks

Cost:£10,000-£50,000+

Root barrier installation

Contains spread, often combined with herbicide

Duration:1-2 weeks

Cost:£5,000-£15,000

Burial on-site

Cheaper than removal, requires space