Extension & Renovation Insurance (UK): A Practical Guide for Homeowners and Contractors

Introduction

Planning a home extension or major renovation is exciting, but it also changes your risk overnight. Once you start knocking through walls, removing roofs, or bringing trades on site, your “standard” home insurance may no longer protect you in the way you expect. Many insurers treat building works as a material change in risk, which can lead to exclusions, higher excesses, or even a declined claim if you haven’t told them.

Extension & renovation insurance (often arranged as a specialist construction insurance policy) is designed to protect the property, the works, and your liability while the project is underway. Whether you’re a homeowner managing a builder, a contractor taking on domestic projects, or a property developer refurbishing to sell, the right cover can be the difference between a manageable setback and a financial disaster.

This guide explains what extension and renovation insurance is, what it typically covers, who needs it, and how to avoid the most common pitfalls.

What is extension and renovation insurance?

Extension and renovation insurance is a specialist policy (or a package of covers) designed for building works on an existing property. It can include protection for:

• The existing structure (the “original” building)

• The new works and materials (the “contract works”)

• Your legal liability to third parties (public liability)

• Employer’s liability (if you employ labour)

• Optional covers like tools, plant, legal expenses, and alternative accommodation

You’ll also hear it described as:

• Renovation insurance

• Home extension insurance

• Builders’ insurance for domestic works

• Contract works insurance

• Contractors all risks (CAR) for smaller projects

The key point: it’s built for the unique risks that happen during construction—fire, theft, storm damage to an open roof, accidental damage, and injuries to third parties.

Why standard home insurance often isn’t enough

Many homeowners assume their buildings insurance continues as normal during a renovation. Sometimes it does for minor works (like redecorating), but major works often trigger restrictions.

Common issues with standard home insurance during works:

• Non-disclosure risk: If you don’t tell your insurer about structural works, claims can be reduced or rejected.

• Exclusions for building works: Policies may exclude damage “arising from alterations” or “contractors’ activities.”

• Unoccupied property rules: Renovations can mean the home is empty for weeks. Unoccupied properties often have strict conditions.

• Increased theft risk: Scaffolding, skips, and open access can increase burglary risk.

• Higher fire risk: Hot works, temporary electrics, and stored materials increase fire exposure.

If you’re doing anything structural—extensions, loft conversions, removing load-bearing walls, or major refurbishments—assume you need specialist advice.

Who needs extension and renovation insurance?

The answer depends on who is responsible for the works and what the builder’s policy does (and doesn’t) cover.

Homeowners

You may need a specialist policy if:

• The works are structural (extension, loft conversion, major reconfiguration)

• The project value is significant

• The property will be unoccupied

• You’re using multiple trades or managing the project yourself

• Your home insurer won’t cover you during the works

Even if your builder has insurance, it may only cover their liability—not your building.

Contractors and builders

If you’re the contractor, you typically need:

• Public liability insurance

• Employer’s liability insurance (if you employ anyone, including labour-only subcontractors in many cases)

• Contract works cover (to protect the works and materials)

• Tools and plant cover (optional)

Domestic projects can be high-risk because homeowners often assume “someone else” is insured. Clear contracts and correct cover protect both sides.

Property developers and landlords

If you’re renovating to sell or let, you may need:

• Renovation-specific buildings insurance

• Unoccupied property cover

• Contract works

• Public liability

If the property is empty, standard landlord insurance may not respond.

What does extension and renovation insurance typically cover?

Policies vary, but these are the core sections to look for.

1) Contract works (the works in progress)

This covers the new building works, materials on site, and sometimes materials in transit.

Typical insured events include:

• Fire

• Flood

• Storm

• Theft (often with conditions)

• Vandalism

• Accidental damage

Key questions:

• Is accidental damage included or optional?

• Are materials stored in the open covered?

• Are high-theft items (copper, lead, tools) restricted?

2) Existing structure (the original building)

This is crucial for extensions and renovations. If a fire starts during the works, you don’t just lose the new extension—you could lose the whole house.

Some policies cover:

• The existing building for specified perils

• The existing building including accidental damage

Make sure the sum insured reflects the full rebuild cost of the property, not the market value.

3) Public liability

Public liability covers your legal liability if a third party is injured or their property is damaged because of the works.

Examples:

• A neighbour trips over building materials on the pavement

• Scaffolding collapses and damages a parked car

• Dust or debris causes damage to a neighbouring property

Limits commonly range from £1m to £5m+ depending on the project.

4) Employer’s liability

If you employ anyone, employer’s liability is a legal requirement in most cases in the UK.

This can apply to:

• Direct employees

• Labour-only subcontractors

Employer’s liability typically provides cover for injury or illness arising from work.

5) Optional covers

Depending on the project, you may want:

• Tools insurance (hand tools, power tools)

• Plant and hired-in plant (mini diggers, breakers, scaffolding)

• Legal expenses (contract disputes, employment disputes)

• Personal accident (income protection for sole traders)

• Alternative accommodation (if the property becomes uninhabitable)

Common exclusions and “gotchas” to watch

This is where most problems happen—when the policy looks fine until you read the conditions.

Hot works restrictions

If the project involves:

• Welding

• Cutting

• Blow torches

• Roofing torches

You may need a hot works permit system and specific fire precautions. Some policies exclude hot works unless strict conditions are met.

Theft conditions

Theft cover may require:

• Secure storage (locked building, locked container)

• Alarmed premises

• Security lighting

• No cover for theft from open sites

If your project is in a high-theft area, ask about higher security requirements.

Unoccupied property conditions

If the property is empty, insurers often require:

• Regular inspections (e.g., every 7 or 14 days)

• Water systems drained down

• Letterbox sealed

• Security upgrades

Failing to follow these conditions can invalidate claims.

Defective workmanship and poor design

Most policies won’t cover:

• The cost of redoing faulty work

• Defective design

However, they may cover resulting damage (e.g., a poorly installed pipe bursts and floods the property). Always confirm the wording.

Subsidence and groundworks

Extensions often involve excavations near existing foundations. Subsidence, heave, and landslip can be excluded or tightly controlled.

If your project includes:

• Basement works

• Underpinning

• Piling

• Deep excavations

Expect additional underwriting questions and possibly specialist cover.

How to choose the right policy (step-by-step)

Here’s a practical checklist to avoid gaps.

Step 1: Define the scope of works

Insurers will ask:

• What work is being done (extension, loft conversion, full refurb)?

• Is it structural?

• Start and end dates

• Total contract value

• Who is the main contractor?

The clearer you are, the easier it is to place cover.

Step 2: Confirm who is responsible for insurance in the contract

Your building contract should state:

• Who insures the existing structure

• Who insures the contract works

• Who covers public liability

If it’s unclear, you risk both parties assuming the other is covering it.

Step 3: Set the correct sums insured

Common sums insured include:

• Existing structure rebuild cost

• Contract works value (materials + labour)

• Contents (if relevant)

Underinsurance can reduce claims payouts.

Step 4: Choose appropriate liability limits

For domestic projects, £2m–£5m public liability is common, but it depends on:

• Proximity to neighbours

• Use of scaffolding

• High footfall areas

Step 5: Disclose key risk factors

Be upfront about:

• Unoccupied periods

• Flat roofs and open roof works

• Listed buildings

• Thatched roofs

• Prior claims

• Previous subsidence

Non-disclosure is one of the fastest ways to create claim disputes.

Typical scenarios (and how insurance responds)

Scenario 1: Fire during a kitchen extension

A temporary electrical fault causes a fire overnight. The new extension and part of the existing property are damaged.

• Contract works cover may pay for the extension rebuild

• Existing structure cover may pay for damage to the original building

• Alternative accommodation may help if you can’t live there

Scenario 2: Theft of materials from site

Copper piping and tools are stolen from an unsecured area.

• Contract works may cover materials if security conditions were met

• Tools cover may respond for stolen tools (often with limits)

Scenario 3: Neighbour’s property damaged

Excavation work causes cracking to the neighbour’s wall.

• Public liability may respond if you’re legally liable

• Subsidence-related claims can be complex—specialist advice matters

Risk management tips that can reduce premiums (and problems)

Insurers like well-managed sites. Practical steps include:

• Use a written contract with clear insurance responsibilities

• Keep the site tidy and secure materials

• Install temporary alarms or CCTV for higher-value projects

• Use lockable containers for tools and copper

• Implement hot works permits and fire watches

• Maintain regular inspections, especially if unoccupied

• Photograph the property before works start (condition evidence)

What information insurers typically need

To quote accurately, expect questions like:

• Property type, age, construction, and location

• Whether it’s occupied during works

• Total rebuild cost and contract value

• Type of works (structural/non-structural)

• Contractor details and experience

• Any previous claims, subsidence history, or flooding

• Security measures on site

• Use of scaffolding and height of works

Having this ready speeds up the process.

How long should the policy last?

Most renovation policies are arranged for a fixed period (e.g., 3, 6, 9, or 12 months) aligned to the build schedule.

If the project overruns (common), you may need:

• An extension of cover

• Updated sums insured

• Updated risk details (e.g., property becomes unoccupied)

Don’t let the policy lapse mid-project.

FAQs

Do I need renovation insurance if my builder is insured?

Often, yes. A builder’s policy may cover their liability, but it may not cover your existing structure or the full value of the works.

Is renovation insurance the same as contract works insurance?

Contract works is usually a key part of renovation insurance, but renovation insurance may also include cover for the existing structure and additional options like alternative accommodation.

What if I’m doing the work myself?

DIY projects can be harder to insure, especially for structural works. You may still be able to arrange cover, but you must disclose that you’re not using a main contractor.

Will my home insurance be invalid during building works?

Not automatically, but it can be restricted. Always tell your insurer before works start and get confirmation in writing.

Does renovation insurance cover poor workmanship?

Usually it won’t cover the cost of redoing defective work, but it may cover resulting damage depending on the policy wording.

Conclusion

Extensions and renovations are one of the biggest investments most people make in their property—and they bring a unique set of risks that standard home insurance may not cover.

The right extension and renovation insurance should protect the existing structure, the works in progress, and your liability while the project is underway. The key is getting the details right: clear responsibility in the contract, accurate sums insured, and honest disclosure about the scope of works and occupancy.

If you want, tell me the type of project (extension, loft conversion, full refurb), approximate budget, and whether the property will be occupied—and I’ll tailor the blog to your exact audience and add a stronger call-to-action for Insure24.