House Extension Insurance: What Cover You Need While You Build

House extensions · Insurance

What insurance you need while an extension is built: what to tell your home insurer and when, what your builder and architect should hold, and a checklist that follows the project from design to completion.

Last updated: 30 October 2026 · Reviewed by Graham Sproul RIBA, Design & Operations Director

AURA is an architecture practice, not an insurer or broker. This guide explains how insurance fits into a building project; for advice on a policy, speak to your insurer or a broker authorised by the Financial Conduct Authority.

What insurance do you need for an extension?

You need your own home insurance to keep working during the build, which may mean extra cover or a specialist renovation policy. Your builder needs its own insurance for the people and the work on site, and your architect and engineer carry professional indemnity insurance for their design. Your building contract decides who insures the existing house and the new work while it’s being built.

Cover	Who holds it	What it’s for	What to ask for
Home buildings and contents insurance	You	Your house and belongings, before, during and after the works	Written confirmation of cover during the build, and any conditions
Renovation or site insurance	You, if your insurer requires it	The house while works are under way or it’s empty	The policy wording on works, unoccupancy and materials on site
Public liability	Your builder	Injury to other people or damage to their property, such as a neighbour’s house	A current certificate, the level of cover, and the dates
Employers’ liability	Your builder, if it employs anyone	Injury to the builder’s own staff; at least £5 million by law	A current certificate
Contract works (all risks)	Your builder or you, as the contract says	The new work and materials until handover	Who insures the works and the existing house, in writing
Professional indemnity	Your architect and engineer	Mistakes in the design or advice	Confirmation that they hold it, and the level; AURA holds £2,000,000 for any one claim

Does your home insurance cover building work?

Often not fully. A standard home policy is written for a house in everyday use, and many limit cover while building work is going on, while contractors are on site, or while the house is empty for a stretch. It’s worth checking the wording before you sign a building contract.

Two gaps catch people out. The first is the house standing empty: if you move out during the works, many policies restrict cover after a set number of days, so check yours. The second is damage from the work itself: many policies exclude damage caused by faulty workmanship, which leaves the question of whether the builder’s insurance pays, and that depends on proof of fault.

Your insurer may offer extra cover for the works, or point you to a specialist renovation policy. If the builder will hold cover that protects the existing house under the contract, your insurer may want to know that too.

Do you need to tell your home insurance about an extension?

Usually, yes: check your policy wording before work starts. Most insurers ask you to tell them about building work and structural changes. The law also says that when you take out or change a policy, you must take reasonable care not to misrepresent your home, so the answers you give at renewal should reflect the extension. Then tell them again when it’s finished.

An extension makes the house bigger, so it usually costs more to rebuild, and new rooms often mean more contents. If the insurer doesn’t know, a claim could be reduced or refused, depending on the policy and what happened. The table sets out what to tell them, and when.

When	What to tell your insurer
Before you sign the building contract	What’s being built, the start and finish dates, who the builder is, and whether you’ll live in the house during the works
Before you move out, if you do	The dates the house will be empty, and check the policy’s unoccupancy terms
If the scope changes	For example a loft added, or a longer programme
At completion	The finished extension, the new rebuild value and any new contents; keep the completion certificate

What insurance should your builder have?

Your builder should hold public liability insurance, for injury to other people and damage to their property, and employers’ liability insurance if it employs anyone, which the law requires at no less than £5 million. Many builders also insure the works themselves until handover. AURA’s building contracts require the contractor to carry public liability insurance of at least £5 million. Ask for the certificates with their price, not on the first day on site.

Check	Why it matters
The certificate is in the company’s legal name	The name on the contract and the policy should match
The policy dates cover the whole build	Cover that lapses halfway leaves a gap
The level of public liability cover	Damage to a neighbour’s house can be expensive
Subcontractors are covered	Most extensions involve several trades
Who insures the works and materials on site	Theft or damage before handover needs an owner
Who insures the existing house during the works	The contract decides; your insurer may need to know

If you’re using more than one contractor, check each one’s cover, and tell your own insurer, because responsibility is split. Check a builder’s reviews and recommendations too, and ask to see proof of their insurance and what it covers.

What does extension insurance cover?

A renovation or extension policy is designed for the risks of the build itself. Policies differ, so read the wording and compare what each insurer covers. These are the risks a policy for extension and renovation work generally addresses, and what to check for each.

Risk	What to check
Damage to your existing property	Whether damage caused by the works is covered, and any faulty workmanship exclusion
Injuries or accidents on site	How it sits alongside the builder’s public and employers’ liability
Theft of contents or building materials	Whether materials stored at the house are covered, and any security conditions
Materials and equipment kept at your home	Who owns them until they’re built in, and whose policy covers them
The property being unoccupied	How many days it can be empty, and what conditions apply

Who insures the works under your building contract?

The building contract should say who insures the existing house, who insures the new work and materials, and what happens if something goes wrong before handover. Get it in writing before work starts. If the contract puts the existing house on you, your home insurer needs to agree to cover it during the works.

On AURA projects, the drawings go to three or four contractors to price, and the building contract is agreed before work starts. We usually use the JCT Minor Works Building Contract with contractor’s design, and on larger jobs the JCT Intermediate Building Contract with contractor’s design. Our contracts require the contractor to carry public liability insurance of at least £5 million.

Who insures the existing house and the works varies by contract. JCT contracts give two main options:

• A joint-names policy taken out by you: one policy, in your name and the contractor’s, covers the existing house and the new works.
• The contractor insures the new works only: the contractor’s policy covers the new work and materials, and the existing house is not part of it, so you need to know how your own policy covers it during the build.

Your architect will set out which option applies in the contract. Before you sign, check with your insurer that your own policy works alongside it.

Your duties under the Construction (Design and Management) Regulations 2015 usually pass to the contractor on a domestic project. Our guide to CDM regulations for homeowners explains how.

A worked example: a rear extension, from design to completion

Take a rear kitchen extension on a Victorian terrace. At design stage, the owners read their home policy and find it limits cover during building work and while the house is empty. At tender, each builder sends insurance certificates with its price. The contract states who insures the existing house and the new work, and the owners call their insurer with the dates and the builder’s name.

The kitchen will be out of use for part of the build, so the family plans to stay away for a few weeks; they check the unoccupancy terms before leaving. Halfway through, the programme slips by a month, so they check the builder’s cover still runs. At completion, they keep the building control completion certificate and tell the insurer about the extra room, so the rebuild value is right.

Where insurance sits among the other steps, such as planning, party wall notices and building regulations, is set out in our guide to the home renovation process.

What can go wrong, and how to avoid it

Most insurance problems on an extension come from gaps between policies: something nobody is covering, or a policy that lapsed or was never updated. A short check at each stage of the project closes most of them.

The builder’s cover lapses mid-job. Check the dates on the certificates against the programme, and ask for renewed certificates if the build runs on.

The house is empty longer than the policy allows. Tell your insurer before you move out and agree the cover for the whole period.

The rebuild value isn’t updated. A bigger house costs more to rebuild. Update it at completion, not at the next renewal.

No completion certificate. Insurers and buyers ask for it. Our guide to building control explains how it’s issued.

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