Knotweed on a new-build plot: NHBC warranty, developer liability and the buyer's options
What to do if knotweed appears in your new-build garden during the NHBC warranty period.
Knotweed appearing in a new-build garden in years 1–3 of ownership is almost always pre-existing — the rhizome was in the soil at handover and merely shooted later. NHBC and most warranty providers will engage with this, provided you have evidence.
What the NHBC Buildmark actually says
Buildmark covers the cost of removing infestations of knotweed where the infestation existed at the time of completion. The burden is on the homeowner to demonstrate that — hence the importance of a dated handover photograph and an early independent survey.
What to do, in order
- Commission a PCA-member surveyor immediately upon discovery.
- Notify the developer in writing the same week.
- Notify NHBC (or your warranty provider) within 30 days.
- Do not attempt DIY treatment — it weakens your claim.
Reviewed by
The survey team
PCA-certificated surveyors, Japanese Knotweed Elimination
PA1 / PA6A certificated surveyors who carry out the site visits, write the management plans and sign off the reports issued to lenders and solicitors.
Reviews the technical, legal and lender statements in this article.
What this page can't tell you
- Guidance is general. Identification, treatment choice and timescales can only be confirmed by a site visit — photographs alone are indicative.
- Lender and insurer requirements vary by institution and change over time. We state what is typically accepted, not what any named lender will accept on your case.
- Guarantee (IBG) eligibility depends on the plan chosen, the survey findings and the underwriter's acceptance. It is not automatic.
- Legal points summarise published law and guidance current at the review date. They are not legal advice.
Last reviewed · Questions on anything stated here: 07582 869979
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