What a structural warranty is
A structural warranty is an insurance-backed promise that the major structural elements of a building remain sound for a defined period — typically 10 years for new builds and large extensions, 12 years for some schemes. It's not a guarantee from the builder (who may not be trading in 10 years' time) — it's an insurance policy underwritten by a regulated insurer, attached to the property, transferable to subsequent owners. The most common warranty providers in London are NHBC (largest, default for new builds), LABC Warranty, Premier Guarantee, BLP, ICW and Buildzone. Each operates on similar terms with minor variations in coverage and claims process.
What's covered
Structural defects in: foundations (subsidence, settlement, heave); load-bearing walls and partitions; roof structure (trusses, rafters, purlins, ridges); chimney structure; floor structure (joists, beams); external claddings where structural; staircases as structural elements; flat roofs as weatherproofing elements; foundations beneath drainage; external rendering bonded to structural walls. The warranty pays for the cost of investigation, repair and reinstatement of the affected element where the defect is the result of the original construction not meeting the warranty body's technical standards.
What's excluded
Standard exclusions: damage caused by client alterations after handover (the warranty doesn't follow your subsequent modifications); damage caused by inadequate maintenance (gutters not cleared, leaks not addressed, decoration not maintained); fair wear and tear; damage from acts of God (lightning, flood, earthquake, war); damage from third-party intervention (vehicle impact, vandalism); cosmetic defects (cracks under 3mm, surface paintwork issues); fittings (kitchens, bathrooms, joinery, finishes — these are covered by separate manufacturer warranties); damage to the contents of the building. Importantly, the warranty does not cover defects in design — that risk is carried by the architect's and structural engineer's professional indemnity insurance.
How claims work
Stage 1 (years 1–2): the builder is liable. You raise the defect with us, we attend within agreed callback time, repair at our cost. Stage 2 (years 3–10): the warranty pays. You raise the defect with the warranty provider, who appoints a loss adjuster, who inspects and instructs repair. The builder is no longer involved (and may not exist). Claims process: notify the warranty body in writing within 30 days of discovering the defect, supply photos and circumstances, allow loss adjuster access for inspection, receive determination within 28 days, work commences typically within 6–8 weeks of determination. The warranty pays the repair cost up to the certificate limit (typically 1.5× original build cost) less the excess (typically £1,000–£2,500).
Transferability and the resale market
Structural warranties transfer automatically with the property — no action needed at sale, no fee, no underwriting. A buyer purchasing a 7-year-old extension or new build inherits the remaining 3 years of warranty. This is a meaningful resale value point: buyers' solicitors check warranty status, and the absence of one materially damages value or pricing. For a London new build, a NHBC certificate adds typically 1.5–3% to resale value versus a property without warranty. For an extension, the impact is smaller but still positive — solicitors view warrantied extensions more favourably than non-warrantied work.
What we do at Builderr
Every Builderr extension, loft conversion, new build and major renovation comes with a 10-year structural warranty as standard. We use NHBC for new builds and major renovations (most recognised brand, highest assignor confidence on resale) and Premier Guarantee for smaller extensions (better cost ratio at lower build values). Warranty registration is included in our quote — no additional fee, no decision required from you. Inspection during the build is by the warranty body's surveyor, in addition to building control. Final Certificate plus warranty certificate is supplied at handover.
