“Fully guaranteed for 10 years” is the most devalued phrase in British building. The guarantee is a promise from a company, and the median small building company doesn’t live 10 years. An insurance-backed guarantee is the version of the promise that survives the promiser.

The three layers of “guarantee”

  1. Your legal rights, exist regardless of any paperwork: reasonable care and skill under the Consumer Rights Act, and the limitation periods that give you six years (sometimes far more) to claim. Free, automatic, but only useful against a builder who still exists and has assets.
  2. The builder’s own guarantee/warranty, a written promise to fix defects for X years. Worth exactly as much as the company’s continued existence and goodwill.
  3. An insurance-backed guarantee (IBG), an insurance policy, in your name, that steps in to honour the builder’s guarantee if the builder ceases to trade. This is the only layer that survives insolvency, the exact scenario in which you’d most need the guarantee.

What an IBG covers (and doesn’t)

Covers: defects that the builder’s guarantee would have obliged them to fix, arising within the policy term, where the builder has ceased trading (some policies also respond if the builder simply refuses and is pursued unsuccessfully). Typical terms run 2–10 years; windows and doors commonly 10, damp-proofing and timber treatment 10–20, general building 2–6.

Doesn’t cover: wear and tear, maintenance, condensation, work outside the guaranteed scope, or, critically, defects while the builder still trades and will attend. It’s a backstop, not a service contract. Claims also require the original guarantee wording, so file both documents together.

Where you’ll meet them

  • Windows and doors, FENSA and Certass installers are required to offer an IBG on every installation; if you weren’t offered one, ask where it is.
  • Damp-proofing and timber, standard via the specialist trade bodies.
  • General building, available but underused: TrustMark-registered firms and members of some trade associations can provide IBGs through approved providers, typically at 1–2% of the contract value. On a £70,000 extension, £700–£1,400 for a decade of insolvency cover is decent value, and asking for one doubles as a solvency test: providers vet the builders they’ll back.

For context, the heavyweight cousin is a structural/latent defects policy (10-year new-build-style cover, underwritten with technical audits), meaningful on self-builds and big structural projects, priced accordingly (often £1,500+).

Checking a guarantee is real

The IBG world has its share of decoration. Verify:

  • An actual policy document in your name, insurer named, policy number, term, scope. A logo on the quote is not a policy.
  • The insurer or scheme exists and is FCA-authorised, search the FCA register; genuine schemes are underwritten by identifiable insurers.
  • What triggers cover, “ceased trading” definitions vary; phoenix companies (same directors, new company) are addressed by better policies.
  • Transferability, good IBGs transfer to the next owner of the house, which quietly adds sale-time value; keep the certificate with your building control paperwork.

Do you actually need one?

Prioritise an IBG where the failure mode is slow and expensive, waterproofing, structural work, basements, roofing, and where you’d struggle to fund the fix twice. Skip it where your retention, Section 75 cover and the modest scale of the job already cap the downside. And never let any guarantee substitute for the protections that prevent problems: vetting, a real contract, and payments that stay behind the work.

This guide is general information for homeowners in England and Wales, not legal advice.