Buildings Insurance During a London Renovation or Extension: What You Need to Know in 2025

**The standard buildings insurance policy — written for an occupied, finished property**:

• A standard UK buildings insurance policy provides cover for the structure of the building against named perils — typically: fire; flood; storm; escape of water; subsidence; malicious damage; theft of fixtures; and accidental damage (where opted into). These perils and their definitions are written for a property that is:
• •In a finished condition (i.e., the building fabric is complete and weather-tight)
• •Occupied by the owner or tenant (the fact of occupation reduces many risks)
• •Not undergoing material alteration

When any of these conditions change — particularly the 'material alteration' condition — the insurer's risk assessment changes, and many standard policy terms come into play.

**Key exclusions that commonly apply during renovation or building works**:

*1. Notification clause (material change of risk)*:

• Virtually all UK buildings insurance policies contain a clause requiring the policyholder to notify the insurer before commencing any 'material change of risk'. A material change of risk includes:
• •Any structural works to the building (demolition; new foundations; steelwork; structural openings)
• •Any extension, addition, or material alteration to the building
• •Extended or partial unoccupancy during works

If the policyholder does not notify the insurer before commencing material building works and a claim arises (e.g., a fire during construction; flooding from the open roof structure of a loft conversion; theft from the building during works), the insurer may reject the claim on the grounds that the risk profile was materially changed without notification. The specific wording varies by insurer and policy — but the notification obligation is standard across most high-street and specialist insurers. **Always notify your insurer in writing before starting any extension, loft conversion, or significant structural work.**

*2. Unoccupied property clauses*:

• Most standard buildings insurance policies contain an 'unoccupied property' clause — cover for named perils is reduced or suspended after the property has been unoccupied for a specified period (typically 30 or 60 consecutive days). During major renovation works, particularly where the property is being completely renovated or where habitable rooms are being extensively altered, the property may become partially or wholly uninhabitable — triggering the unoccupied property clause. Typical exclusions under the unoccupied clause:
• •Escape of water (burst pipes; leaking roofs) — arguably the most common and costly renovation-period claim
• •Malicious damage (vandalism) and theft
• •Storm damage to weather-exposed elements (particularly relevant when the roof is stripped for a loft conversion)

Where the policyholder moves out during works, the insurer must be told — and the period of unoccupancy and the reason for it must be disclosed. Many insurers will continue cover during renovation unoccupancy if told in advance, but some require a policy endorsement (an addition to the policy terms) or a specific renovation policy.

*3. Exclusion of loss arising from the works themselves*:

• Standard buildings insurance policies typically exclude cover for loss or damage arising directly from the construction works themselves — for example:
• •Damage caused by the contractor's work to the existing structure (a contractor drilling through a wall and fracturing a water pipe — the resultant damage is caused by the works, not by a named peril)
• •Defective workmanship (a loft conversion that leaks because the contractor's waterproofing failed)
• •Loss or damage to materials and equipment on site (tools; materials stored on site; scaffolding)

These risks are covered by the **contractor's own insurance** — not by the homeowner's buildings insurance. This is why contractor insurance is a critical check before appointing any contractor for a London extension (see Section 2).

**What to do before starting works — the practical steps**:

*Step 1 — Review your policy*: Read the current buildings insurance policy carefully for: notification obligations; material change of risk wording; unoccupied property clause; and what is excluded during building works. If in doubt, call your insurer's policyholder helpline and ask them to confirm the position in writing.

*Step 2 — Notify your insurer in writing*: Before building works begin, write to (or email) your insurer with: the nature of the works (extension; loft conversion; refurbishment); approximate duration; approximate contract value; whether the property will be vacated during works; and name of the main contractor. Keep a copy of the notification and the insurer's written response — if a claim arises, this written trail demonstrates that you fulfilled your disclosure obligation.

*Step 3 — Ask the insurer to confirm continued cover or to issue an endorsement*: Some insurers will simply acknowledge the notification and confirm the existing policy continues (possibly with modified terms). Others will issue a renovation endorsement (an addition to the policy specifically covering the renovation period — sometimes at additional premium). A small number will decline to continue cover during significant structural works — in which case you will need a specific renovation or self-build policy.

*Step 4 — Consider a specialist renovation insurance policy*: For major works (full refurbishment; new extension over £80,000 contract value; loft conversion involving complete roof removal), a specialist renovation insurance policy (from insurers such as Self Build Zone; BuildStore; Protek; Adrian Flux; or via specialist brokers) may provide more comprehensive cover than an endorsed standard policy. These products are designed specifically for the renovation period and typically cover: the existing building fabric; the new works materials on site; contract works risk; and may include an element of employer's liability (where the homeowner is directly employing anyone on site — see Section 3 for contractor insurance).

**The contractor's insurance is separate from the homeowner's insurance — both are necessary**:

A common misunderstanding is that the homeowner's buildings insurance covers all risks on a building project. It does not — and the contractor's insurance does not cover the homeowner's property in the same comprehensive way the homeowner's own policy does. The two layers of insurance work together:

• •**Homeowner's buildings insurance**: covers the homeowner's existing building fabric against named perils (fire; storm; escape of water; etc.) — modified as described in Section 1 during works
• •**Contractor's insurance**: covers the contractor's liability for damage they cause; the contractor's equipment and materials; their employees' or sub-contractors' work injuries; and the contract works themselves during the construction phase

**The three core insurance policies a reputable London building contractor should hold**:

*1. Public Liability Insurance (PLI)*:

• Public Liability Insurance covers the contractor's legal liability for:
• •**Injury to a third party** (a member of the public, the homeowner, or someone visiting the site who is injured as a result of the contractor's negligence — a falling tool from scaffolding; an uncovered trench; a temporary support that collapses)
• •**Damage to third party property** (the contractor accidentally damages the homeowner's property; the neighbouring property; or any third party's property — e.g., a digger that ruptures a water main under the garden; a scaffold board that falls and breaks the neighbour's conservatory)

• Minimum PLI level for a London residential contractor undertaking extensions and refurbishments:
• •**£1,000,000 minimum**: the absolute minimum for any residential contractor
• •**£2,000,000**: the minimum standard for a reputable contractor working on London projects over £50,000 contract value — this is the level specified by most principal contractor accreditation bodies (FMB; TrustMark; Checkatrade)
• •**£5,000,000**: appropriate for larger residential projects; any project involving party wall work; or any project in a densely populated London area where third-party risk is elevated

**RCB Design & Build holds public liability insurance at the levels appropriate to the projects we undertake — a copy of our current insurance certificate is available on request before contract signing.**

*2. Employers' Liability Insurance (ELI)*:

Employers' Liability Insurance (ELI) is a **legal requirement** under the Employers' Liability (Compulsory Insurance) Act 1969 for any employer who employs workers in Great Britain. ELI covers the employer's legal liability for injury or illness suffered by their employees while working for them.

Minimum required by law: **£5,000,000** (though in practice, virtually all ELI policies are written for £10,000,000 or more).

For a London building project: the contractor must hold ELI if they employ any person (full-time; part-time; casual; or day-labourer). Sole traders with no employees are exempt but are only truly exempt if they genuinely have no employees — if they engage 'self-employed' sub-contractors who are actually employed under test, the exemption may not apply. A homeowner who pays workers directly (rather than through a contractor) may themselves become an employer for ELI purposes — always use a contractor rather than engaging workers directly.

*3. Contract Works Insurance (Contractors' All Risks — CAR)*:

• Contract Works Insurance (also called Contractors' All Risks or CAR) covers:
• •**The works themselves** — materials and constructed works on site against accidental damage, fire, flood, storm, and theft during the construction phase. For example: a new timber-frame extension structure is destroyed by fire before the roof is made weathertight — Contract Works insurance covers the cost of rebuilding the destroyed work
• •**Materials on site** — building materials stored on site pending installation (timber; tiles; insulation; kitchen units delivered and awaiting installation) against theft and accidental damage

• Contract Works insurance is not legally mandatory but is standard practice for reputable UK building contractors. The homeowner should ask:
• •Does the contractor hold CAR insurance?
• •What is the single-contract limit (the maximum value of any single contract the policy will cover)? The contract value of the London extension must be within the contractor's CAR limit
• •Does the CAR policy cover materials stored on site prior to installation? (Some policies only cover installed works — not materials in storage)

**How to verify contractor insurance before signing a building contract**:

*Request insurance certificates*:

• Before signing any building contract, ask the contractor to provide:
• •Current Public Liability insurance certificate (confirming level and policy period)
• •Current Employers' Liability insurance certificate (confirming legal compliance; level; policy period)
• •Contract Works insurance certificate where relevant (for contracts above approximately £50,000 value)

• *Check the certificate is current*:
• •Insurance certificates have an expiry date — check that the policy period covers the expected construction period (or that the contractor will maintain cover throughout). An extension project starting in October 2025 running to March 2026 needs cover through March 2026 at minimum
• •The policy holder name on the certificate should match the contractor name on the building contract

• *Third-party verification*:
• •For accreditation bodies like FMB (Federation of Master Builders); TrustMark; Checkatrade; and NICEIC, insurance maintenance is a condition of accreditation — their website allows you to verify current membership
• •Insurers can confirm a certificate as genuine if you suspect it may not be authentic — call the insurer listed on the certificate with the policy number to verify

**The specific risks that arise during London building works — what homeowners often don't anticipate**:

*1. Subsidence and third-party damage during excavation*:

For London extensions involving excavation (foundations; drainage; new basement — see `basement-conversion-costs-guide`), the risk of causing subsidence or settlement damage to neighbouring properties exists during and after construction. London clay is particularly susceptible to shrink-swell behaviour, and excavation close to party walls can cause soil movement that affects neighbouring foundations.

• Coverage implications:
• •The contractor's PLI covers damage caused to the neighbour's property by their negligence — if the excavation was not designed or executed properly and the neighbour's property settles as a result, the contractor is liable
• •If the settlement is caused by an inherent ground condition (not contractor negligence) and was not foreseeable, the position is more complex — this is where the Party Wall Act Surveyor's role and the geotechnical investigation (see `underpinning-costs-guide`) become important
• •The homeowner's buildings insurance does not cover damage caused to a neighbour's property — that is the contractor's PLI claim, not the homeowner's

*2. Theft of materials and tools on site in London*:

London building sites — particularly domestic rear extensions with easy garden access — are targets for theft of materials (copper pipe; aluminium; tools; timber). Standard buildings insurance typically excludes theft of building materials on site. The contractor's CAR insurance covers materials on site — but it is worth discussing with the contractor what their CAR policy's single-incident and annual aggregate limits are for on-site theft.

Practical mitigation: site security (locking gates; securing scaffolding access at close of day; not storing expensive materials on site in advance of installation — deliver just-in-time); CCTV on the existing house that overlooks the extension site.

*3. Damage from temporary weather exposure during works*:

• An extension project involves stages where the structure is temporarily weather-exposed — the rear wall is demolished before the new extension roof is made weathertight; a loft conversion involves stripping the existing roof before the new structure is in place; a flat roof replacement leaves the building temporarily unprotected. During these stages:
• •The contractor's CAR policy covers damage to the works themselves (the new extension or loft structure is damaged by a rainstorm while not yet weathertight)
• •The homeowner's buildings insurance — if properly notified — should still cover the existing house against storm damage during works; but the interface between 'existing building' and 'works' can be ambiguous when the two are physically connected
• •**The contractor must ensure temporary weather protection** at all exposed stages — temporary weatherproof membranes (Visqueen sheeting over cut rafters; temporary flat roof membrane before permanent waterproofing; boarding up of structural openings before windows are installed). This is a contractual and insurance obligation.

*4. Neighbour and third-party property during scaffolding*:

Scaffolding on London terraces almost always uses the public footpath and/or the adjacent property's airspace. Licences may be required (Local Highway Authority for footpath scaffold; Party Wall Agreement or licence to encroach for airspace over the neighbour's property). If a third party is injured by scaffolding (a member of the public walks into an improperly lit scaffold on the footpath; a scaffolding board falls and damages the adjacent property's roof), the scaffold contractor's PLI and the main contractor's PLI both respond. Ensure the scaffolding sub-contractor holds their own independent PLI.

**Structural warranties (latent defects insurance) — what they are and when they matter**:

• A structural warranty (also called a latent defects insurance policy or new build warranty) provides long-term protection against major structural defects that are not immediately apparent at completion — defects that emerge years after the work is done. The best-known products are:
• •**NHBC Buildmark** (typically for new build homes; not generally available for extensions to existing homes)
• •**Premier Guarantee** (available for extensions, conversions, and refurbishments as well as new build)
• •**Build-Zone** (residential extensions and conversions)
• •**LABC Warranty** (backed by Local Authority Building Control; available for extensions and conversions)

• For a London rear extension or loft conversion, a structural warranty is not legally required — but it provides important protection for the homeowner (and for future buyers of the property) against latent structural defects. The warranty is typically issued for 10 years and covers:
• •Foundation failure or inadequate design
• •Structural frame failure
• •Roof structure failure
• •Waterproofing failure (for basement conversions and flat roofs)

• *When a structural warranty is particularly important*:
• •Where the property is to be sold within 5–10 years of the extension works — mortgage lenders will sometimes require a structural warranty for newly built extensions as a condition of the mortgage on resale. Without a warranty, the buyer may be unable to get a mortgage on the property with the extension included in the valuation
• •Where the extension is a complex structural scheme (basement; structural alterations; large flat-roof extension) where latent defects in waterproofing or structure are more likely
• •Where the contractor does not provide a long-term guarantee on their workmanship (a structural warranty from an independent insurer provides a backstop that the contractor's personal guarantee does not)

Cost of structural warranty for a London residential extension: typically £600–£2,500 for a 10-year policy, depending on the contract value and the warranty provider. An inspection fee is usually included — a warranty inspector visits the site at key stages to confirm work quality before the warranty is issued.

**Summary of insurance actions for a London building project**:

1. Notify your buildings insurer in writing BEFORE works begin — describe the works; contract value; duration; occupancy status; and contractor name 2. Get the insurer's written acknowledgement and confirmation of continued cover (or endorsement terms) 3. Request contractor's PLI; ELI; and CAR certificates before signing the building contract 4. Check PLI level (minimum £2,000,000 for a reputable London contractor on a residential project; £5,000,000 for complex or high-value works) 5. Verify certificate currency (must cover the full construction period) 6. Consider a specialist renovation insurance policy for major works (full refurbishments; contracts over £80,000; complete roof removal) 7. Consider a structural warranty for 10-year latent defect protection, particularly if resale within 10 years is likely