The short answer
A treatment guarantee is the contractor’s own promise to re-treat if knotweed regrows; an insurance-backed guarantee (IBG) adds an insurer that honours that promise even if the contractor stops trading. Lenders almost always want an IBG, typically for around ten years. The IBG is the difference between a guarantee a mortgage lender will accept and one they will not.
“Guaranteed” can mean very different things. A contractor’s own guarantee is only as good as the contractor; an insurance-backed guarantee survives the contractor going out of business. Because a mortgage may last decades, lenders care which one you have. This page explains both, the typical term, and what to check before relying on a guarantee.
Guarantees at a glance
- Treatment guarantee Contractor’s own re-treat promise
- Insurance-backed (IBG) Honoured even if the firm folds
- Typical IBG term Often around 10 years
- Lenders want An IBG, not just a company guarantee
- Provided by PCA-accredited firms
Treatment guarantee vs insurance-backed guarantee
A treatment guarantee is the contractor’s own commitment: if the knotweed regrows within the guarantee period, they will return and re-treat at no extra cost. It is a useful promise — but only while the company exists.
An insurance-backed guarantee (IBG) sits on top of that. A separate insurer underwrites the guarantee so that, if the original contractor ceases trading, an alternative will complete the work or the cost is covered. Because a mortgage can run for 25 years or more, lenders want the protection that survives the contractor — the IBG.
| Treatment guarantee | Insurance-backed guarantee | |
|---|---|---|
| Backed by | The contractor only | An insurer + the contractor |
| If firm folds | Worthless | Still honoured |
| Lender view | Often insufficient | Usually accepted |
| Typical term | Varies | Often around 10 years |
How long does cover last?
An insurance-backed guarantee commonly runs for around ten years, though the exact term varies by provider and policy. The guarantee should be transferable to a future buyer — an important point when selling, because the buyer’s lender will want the remaining cover in their name.
- Check the IBG is in place from the outset, not promised later.
- Confirm the term and that it is transferable on sale.
- Keep the certificate with the property paperwork.
- Make sure the firm is PCA-accredited — that is what makes an IBG available.
Why lenders insist on it
An IBG is the linchpin of a mortgage offer on a knotweed-affected property. Combined with a survey and a management plan, it gives the lender confidence the risk is controlled for the life of the loan. Without it, the lender may decline or impose a retention.
Get a guaranteed treatment plan
Instruct a PCA-accredited specialist and secure an insurance-backed guarantee your lender will accept — transferable when you come to sell.
Frequently asked questions
What is an insurance-backed guarantee?
It is a guarantee underwritten by an insurer, so the cover holds even if the treating company stops trading — which is why lenders want it.
How long does a knotweed guarantee last?
An insurance-backed guarantee commonly runs for around ten years, though the exact term depends on the provider.
Is the guarantee transferable when I sell?
A proper IBG should be transferable to the buyer; confirm this, as the buyer’s lender will want the remaining cover.
Will a contractor’s own guarantee satisfy my lender?
Usually not on its own — lenders typically require an insurance-backed guarantee from an accredited firm.
Sources & further reading
- Property Care Association (PCA) — insurance-backed guarantees for invasive weed treatment
- RICS — Japanese Knotweed and Residential Property guidance note (2022)
- GOV.UK — Prevent Japanese knotweed from spreading
This guide is general information, not a site-specific survey or legal advice. Japanese knotweed treatment and removal should be assessed by a PCA-accredited specialist before you act.