Structural Warranties for New Builds and Extensions: What They Cover and Do You Need One?

**What structural warranties cover**:

A structural warranty (commonly 10 years in duration) provides insurance-backed protection against latent structural defects — that is, defects in the structure of a newly built or converted property that were not apparent at the time of handover but manifest within the warranty period. Covered defects typically include:

• •Structural defects in the foundations, substructure, external walls, roof structure, and floor structure
• •Waterproofing defects in below-ground structures (basements)
• •Defects in the structural systems that result in physical damage to the building

• *What structural warranties do NOT cover*:
• •Fair wear and tear
• •Defects that result from damage by the occupant or maintenance failures
• •Non-structural elements (joinery, mechanical and electrical installations, decoration)
• •Defects that were apparent at handover (a warranty is for latent defects, not known defects)
• •In most policies: consequential losses beyond the physical repair cost of the defective element

**The main structural warranty providers in the UK**:

| Provider | Products | |---|---| | NHBC (National House Building Council) | Buildmark (the most widely recognised; required by most high-street lenders for new-build homes; only available through NHBC-registered builders) | | Premier Guarantee | 10-year structural warranty for new builds and conversions | | Protek | 10-year structural warranty for new builds, conversions, and self-builds | | Build-Zone | Insurance-backed warranties for new builds, major conversions, and basement works | | LABC Warranty | Local Authority Building Control warranty — provides 10-year warranty through the local authority Building Control inspection process | | ICW (International Construction Warranties) | 10-year warranty, particularly for self-build and custom build | | Global Home Warranties | New build and conversion warranties | | Checkmate | Structural warranties for new build and major refurbishments |

**When a structural warranty is required by lenders**:

Mortgage lenders in the UK place specific requirements on properties that are:

*New-build properties (under 10 years old)*: Most UK mortgage lenders (following Council of Mortgage Lenders / UK Finance guidance) require a 10-year structural warranty on new-build properties — either an NHBC Buildmark, or an alternative acceptable warranty from the above list. Without a structural warranty, the lender typically will not lend on a new-build property. The warranty is required at the time of purchase and must be transferable to subsequent buyers within the 10-year period.

*Self-build properties*: A self-build home (including a home built by a main contractor for a self-building client) requires either a structural warranty or a Professional Consultant's Certificate (PCC) from a chartered structural engineer or architect who has inspected the works at key stages. Many lenders prefer a structural warranty over a PCC for self-builds.

*Conversion properties (change of use, barn conversion, basement conversion)*: Some lenders require a structural warranty for conversions of non-residential buildings to residential use. This is particularly common for: barn conversions; commercial-to-residential conversions; basement conversions where significant structural works were undertaken.

• *When lenders do NOT typically require a structural warranty*:
• •Extensions to an existing residential property (where the existing property was built under a structural warranty or is more than 10 years old)
• •Internal refurbishments of an existing property
• •Like-for-like replacements of structural elements in an existing building (re-roofing, underpinning of an existing structure)

**Professional Consultant's Certificate (PCC) as an alternative**:

A PCC is a signed certificate from a qualified professional (a chartered structural engineer or chartered architect with appropriate PI insurance) who has inspected the building at key stages of construction and certifies that the works have been carried out in accordance with the drawings and specification. Many lenders accept a PCC for extension and conversion projects where a full structural warranty is not available or is disproportionate to the project scale. The PCC must be on the professional's letterhead, signed in their personal capacity, with evidence of current PI insurance.

For extensions in London: a PCC from the structural engineer (who has inspected at foundation, structural frame, and pre-closing stages) is the standard approach — the structural engineer signs the PCC as part of their inspection service.

**The inspection regime during construction**:

A structural warranty is not simply a policy purchased at the end of construction. The warranty provider conducts (or requires evidence of) independent inspections during construction at key stages. These inspections are the basis on which the warranty provider accepts the risk of insuring the completed building. Typical inspection stages:

| Stage | What is inspected | |---|---| | Commencement / ground preparation | Subsoil conditions, DPC/DPM, drainage routes | | Foundations | Foundation depth, type, and construction per design | | Substructure / basement | Waterproofing installation, structural concrete, below-ground elements | | Superstructure / structural frame | Structural walls, columns, beams, floor and roof structure | | Pre-closing (before rendering or plasterboarding) | Insulation, cavity closers, lintels, tie positions | | Weathertight / roof | Roof structure, covering, drainage, flashings | | Pre-handover | Completion of critical elements before Certificate issued |

The warranty provider inspects independently (or through an approved inspector) — the inspections are distinct from Building Control inspections (which are statutory). Many projects use a combined LABC Warranty service where the local authority Building Control and the warranty provider's inspections are co-ordinated.

**The two periods in a structural warranty**:

*The Defects Insurance Period (typically years 1 and 2)*:

During the first 2 years, the warranty covers defects that result from the builder not meeting the warranty provider's technical standards — this is a broader cover than structural defects alone. During this period, the builder is primarily responsible for rectifying defects; if the builder fails or is unavailable, the warranty insurer steps in. This period is similar in concept to the contractor's rectification/defects liability period in a building contract.

*The Structural Insurance Period (typically years 3–10)*:

From year 3 to year 10, the warranty covers only latent structural defects — defects in the structure that result in or have the potential to result in physical damage to the building. The insurer (not the builder) is directly responsible for the claim during this period.

**Making a claim under a structural warranty**:

1. *Notify the warranty provider* in writing when a structural defect is discovered, within the 10-year period 2. *The warranty provider investigates* — appointing a surveyor to assess whether the defect is covered (i.e., a latent structural defect within the scope of the policy) 3. *If covered*, the warranty provider arranges or funds the repair 4. *If disputed*, the policy will include a dispute resolution procedure (typically ADR — alternative dispute resolution — before litigation)

*Common reasons for claims being declined*: the defect is cosmetic rather than structural; the defect results from maintenance failure (gutters not cleaned, allowing water ingress); the defect was apparent at handover and not recorded in a snagging list; the defect results from the occupant's alterations after the warranty period began.

**Structural warranty costs (London 2025)**:

Structural warranty premiums are set by the warranty provider based on the construction value of the project, the type of structure, and the level of risk. For residential projects:

| Project type and approximate build cost | Typical warranty premium | |---|---| | New-build house, £300,000 build cost | £3,000–£6,000 | | New-build house, £600,000 build cost | £5,500–£10,000 | | Major conversion (barn, commercial-to-resi), £250,000 build cost | £3,000–£7,000 | | Basement conversion with structural works, £150,000 build cost | £2,000–£5,000 | | Extension (where warranty required), £80,000 build cost | £800–£2,000 |

Note: NHBC Buildmark premiums are set by NHBC and are not published on a standard scale — contact NHBC or a registered NHBC builder for a specific quote.

*Typical inspection costs*: In addition to the policy premium, the warranty provider charges for site inspections — typically £500–£1,500 total for a residential self-build or major conversion, depending on the number of inspections required. Some providers bundle inspection costs into the premium; others charge separately.

**The self-build scenario**:

For a London client self-building (commissioning a main contractor to build a new home on their own land), the warranty process works as follows:

1. The warranty provider is engaged at the start of the project — before construction commences 2. The warranty provider reviews the design (drawings and structural specification) 3. Inspections take place at the stages above during construction 4. At practical completion, the warranty provider issues the Certificate of Structural Adequacy (or equivalent) — this is the document the mortgage lender requires 5. The 10-year warranty runs from the date on the certificate

*Key issue for self-builds*: The warranty must be arranged BEFORE construction starts — a warranty provider will not inspect a completed building and issue a warranty retrospectively (they cannot assess what happened in the hidden structural layers that are now concealed behind plasterboard and finishes). A self-build without a warranty — or where the warranty inspection process was not followed — may struggle to obtain a mortgage when the property is completed.

**What to do if you are buying a property without a structural warranty**:

Older new-build properties (built more than 10 years ago) and many conversion properties do not have a current structural warranty (either it was never obtained, or the 10-year period has expired). For buyers of these properties:

• •*Structural survey*: Commission a full structural survey (RICS Level 3 Building Survey) from a chartered structural surveyor before exchange of contracts; the surveyor will identify visible structural defects and flag any concerns about the structural integrity
• •*Professional Consultant's Certificate*: If the property was built less than 10 years ago without a warranty, some lenders may accept a retrospective PCC from a chartered surveyor who inspects the property (a less thorough process than a construction-stage inspection but accepted by some lenders)
• •*Indemnity insurance*: A structural defect indemnity insurance policy can sometimes be obtained for a property built without a warranty — the cost is higher than a standard warranty but may be acceptable to lenders for older new-builds
• •*Ask the solicitor*: The property solicitor will flag if the lender requires a warranty or PCC; if the lender will not lend on a property without a warranty, this is a title/mortgage issue to resolve before exchange