Standard home insurance usually stops short of covering major building work, and starting an extension, loft conversion or garage conversion without telling your insurer can invalidate your entire policy. Before any structural work begins, contact your insurer and arrange the right specialist cover, whether that is homeowners’ building works (HBW), contract works, or renovation insurance. This guide breaks down which policy does what.
TL;DR:
- Most standard home policies exclude building work, making specialized cover like homeowners’ building works essential before starting any structural project.
- Contractor insurance protects their work and liabilities but does not cover your existing structure or contents, so homeowners must arrange separate policies.
- Insurers require upfront notification of building projects, preferably in writing, to prevent gaps in coverage and avoid claim rejections due to underdeclaration or unapproved work.
- Failure to declare work, relying solely on contractor insurance, or underinsuring rebuild costs are common pitfalls that void claims and leave homeowners financially exposed.
- Coordinating documentation, project details, and insurer communication before work begins ensures smoother claims processes and reduces disputes during renovations.
Table of Contents
- What types of building work insurance UK homeowners actually need
- Who arranges each policy and what falls to you
- When must you tell your insurer about building work?
- Common pitfalls that void building work insurance
- Step-by-step checklist to get insurance-ready before work starts
- How Complete-Property-Solutions helps with insurance-ready paperwork
- How building work insurance claims are handled
- How long should your building insurance cover last?
- Questions to ask your insurer or broker before work starts
- What happens if you skip building work insurance
- The real problem isn’t the policy, it’s the timing
- Need help preparing your insurance-ready paperwork?
- Sources
What types of building work insurance UK homeowners actually need
Your existing buildings and contents policy covers the house as it stands today. It was never designed for a builder ripping out a wall or a skip full of rubble sitting on your drive for six weeks. That gap is where most disputes and rejected claims start.
Contract works insurance (sometimes called contractors all risks) covers the building materials, half-finished structure, and site itself against fire, theft, and storm damage while the project is underway. It is usually taken out by the contractor, but it protects the works, not your existing house.
Homeowners’ building works (HBW) cover takes a different approach. It wraps your existing structure, the contract works, and often your contents into one seamless policy, which removes the grey area between “whose insurance covers what” that causes so many arguments after something goes wrong. HBW policies are built specifically to satisfy contract clauses on major projects, and Plum Underwriting notes that a single combined policy speeds up claims handling because there is only one insurer to deal with.
You should also understand the difference between:
- Public liability insurance, covering injury to a third party or damage to a neighbour’s property caused by the building work
- Employers’ liability insurance, a legal requirement for any contractor employing staff on site
- Alternative accommodation cover, which pays for temporary housing if the works make your home uninhabitable
- Accidental damage cover, often an optional extra rather than a standard inclusion
Crucially, Aviva is clear that a builder’s public liability certificate does not replace your own buildings cover. Your contractor’s insurance protects their work and their liability to third parties. It does nothing for your existing walls, roof, or contents if a pipe bursts during the build.
Who arranges each policy and what falls to you
Your contractor typically arranges contract works cover for the build itself, insuring materials and unfinished structure until handover. As the homeowner, you remain responsible for insuring the existing house and its contents throughout, unless your contract states otherwise.
Contracts built on JCT-style wording often specify that cover must be held in joint names, meaning both you and the contractor are named on the same policy. This avoids one party’s insurer refusing a claim on the grounds that “it wasn’t our risk.” Before signing anything, check:
- Whether your contract requires joint-names cover, and who is responsible for arranging it
- That your contractor’s public and employers’ liability certificates are current, not expired
- Your policy’s start and end dates against the project’s realistic timescale
- Whether your mortgage lender needs written confirmation that adequate cover is in place
When must you tell your insurer about building work?
Always notify your insurer before work starts on any extension, loft conversion, garage conversion, or structural knock-through, and immediately if the property will stand empty during the build.
Many insurers set a project value above which standard home cover simply will not stretch. Hiscox highlights that projects often exceeding a moderate value commonly need specialist renovation or HBW cover rather than a tweak to your existing policy, though limits vary considerably between providers, so check yours directly.
Pro Tip: Notify your insurer in writing, even if you also phone them, and keep the confirmation email. If a claim ever arises, a dated written record of what you declared and when is worth far more than a remembered phone call.
Treat notification as step one, not an afterthought. Which? advises doing this before the first spade goes in the ground, because notifying after work has started can leave you with an uninsurable gap for anything that happens in between.
Common pitfalls that void building work insurance
Rejected claims during renovations follow a handful of familiar patterns, and most are avoidable with a five-minute policy check before work starts.
- Unoccupancy limits. Most policies restrict how long a property can sit empty before cover lapses or reduces significantly. If you are moving out during a big renovation or garage conversion, check this figure specifically.
- Missing accidental damage cover. Which? research shows that only a minority of standard policies include accidental damage as standard, so scaffolding scrapes or a dropped tool through a ceiling may not be covered unless you have added this extra.
- Weather exclusions on unfinished work. An open roof during a loft conversion is far more exposed to storm damage, and some insurers exclude weather-related claims on unfinished structural work entirely.
- Relying solely on the builder’s insurance. Contractor liability cover protects them, not your existing structure or belongings.
- Underinsuring the rebuild cost. If your sum insured hasn’t been updated to reflect the finished project’s value, you could be significantly short in a total loss scenario.
- Failing to declare the works at all. This is the single most common reason insurers cite for rejecting a claim outright.
Step-by-step checklist to get insurance-ready before work starts
Getting the paperwork right before the first delivery van arrives saves weeks of back-and-forth later.
- Gather your contract details. Note the total contract value, start date, and realistic completion timescale.
- Request contractor certificates. Ask for current public liability and, if they employ staff, employers’ liability certificates, plus evidence of contract works cover.
- Contact your insurer or a specialist broker. Notify them of the works and request an HBW or renovation quote if your project exceeds their standard threshold.
- Confirm cover in writing before any structural work begins, and file the confirmation alongside your contract.
- Keep records throughout. Photos of progress, receipts for materials, correspondence with your insurer, and all contractor certificates should sit in one folder.
If your existing insurer declines to extend cover, a specialist broker can usually arrange HBW or renovation insurance quickly, but get this sorted before works begin, not once the skip has arrived. Our guide to house renovation stages covers the wider project timeline this paperwork needs to fit around.
How Complete-Property-Solutions helps with insurance-ready paperwork
Arranging cover is always the homeowner’s responsibility, but a well-organised builder makes that job far easier by having the right paperwork ready before you even ask.
Complete-Property-Solutions has worked across the North West for more than 35 years, and that experience shows in how projects are documented from day one. The company keeps current liability certificates and contract works evidence ready to hand to your insurer or broker without delay.
For homeowners in local areas, this means:
- Fixed-price quotations that give your insurer a clear contract value from the outset
- Contractor certificates supplied promptly, not chased for weeks
- Clear project timescales that match what you declare to your insurer
How building work insurance claims are handled
Most claims during renovation fall into a few recognisable categories: storm damage to an open roof, theft of materials from an unsecured site, accidental damage from tools or scaffolding, or a burst pipe disturbed during structural work. How smoothly these are resolved depends almost entirely on what was arranged before work started.
Under a combined HBW policy, a single insurer assesses the whole claim, existing structure and contract works together, which usually means fewer arguments about whose policy is responsible for what. Where cover is split between the homeowner’s buildings policy and the contractor’s contract works insurance, claims can stall while two insurers debate liability, particularly if damage affects both the new build and the existing structure at the same point, such as where an extension joins the original house.
To avoid disputes, document everything as you go. Photograph the site weekly, keep dated correspondence with your insurer about what you declared, and retain your contractor’s certificates on file, not just a verbal assurance they exist. If damage occurs, report it to your insurer immediately rather than waiting until the contractor has “sorted it,” since unreported damage can complicate a later claim considerably. Where a dispute does arise over which policy should pay, having a written record of when you notified your insurer and what they confirmed in response is usually the deciding factor.
How long should your building insurance cover last?
Cover needs to run for the full length of your project, plus a sensible buffer. A straightforward kitchen extension might complete in eight to twelve weeks, while a wraparound extension or loft conversion with planning permission attached can run four to six months once design, Building Regulations approval, and construction are all accounted for.
Match your policy period to a realistic timescale, not the contractor’s most optimistic estimate. Weather delays, material shortages, and Building Control sign-off can all push a project past its original completion date, and if your specialist cover expires while scaffolding is still up, you are exposed for the remainder of the build. Ask your insurer or broker for a policy period with a built-in extension option, or confirm in writing what happens if the project overruns.
For most homeowners, the safest approach is to insure for the contract timescale plus an extra four to six weeks. It costs little extra and avoids the awkward scramble of renewing cover mid-project because the roofers ran two weeks behind schedule.
Questions to ask your insurer or broker before work starts
Getting straight answers to a short list of questions before signing anything prevents most of the disputes that surface later.
- What is your project value threshold before I need specialist cover rather than my standard policy?
- Does this policy cover the existing structure and the contract works together, or only one?
- What is the unoccupancy limit if I need to move out during the build?
- Is accidental damage included, or do I need to add it separately?
- Does cover extend to alternative accommodation if the property becomes uninhabitable?
- What happens if the project overruns the policy period?
- Do you require joint-names cover under my building contract, and who arranges that?
Write the answers down. A broker’s verbal reassurance is far less useful than a policy schedule confirming exactly what is and isn’t included.
What happens if you skip building work insurance
Going without appropriate cover during a renovation is one of the costliest mistakes a homeowner can make, and the risk rarely shows itself until something has already gone wrong.
If your insurer later discovers undeclared structural work, they can void your entire policy, not just the claim connected to the building project. That means a completely unrelated event, a burst pipe in the bathroom or a break-in at the front door, could go uncovered simply because the renovation wasn’t declared. Underinsuring the rebuild cost carries a similar sting: after a serious fire or storm, you could find yourself thousands of pounds short of what it actually costs to reinstate the property, particularly once you factor in the increased value a finished extension adds to the rebuild figure.
There is also the financial exposure from third-party claims. Without adequate public liability cover in place, a neighbour’s damaged fence or a passer-by injured by falling debris becomes a personal liability, potentially running into tens of thousands of pounds in a serious case. For a project costing £30,000 to £80,000, the cost of appropriate insurance is a small fraction of the risk it removes.
The real problem isn’t the policy, it’s the timing
Homeowners rarely lose out because they picked the “wrong” insurance product. They lose out because they arranged it too late, after the contract was signed, sometimes after the skip arrived. The conventional advice tells people to “get adequate cover,” which is true but useless without a trigger point telling them when.
My honest read on this: the threshold that insurers like Hiscox reference isn’t a hard rule, it’s a prompt. Treat any structural project, regardless of cost, as a notify-now situation. A £15,000 garage conversion that goes wrong because nobody told the insurer causes exactly the same heartache as a £60,000 extension that does.
What gets overlooked is the value of a single combined HBW policy over separately arranged cover. It costs a little more upfront, but it removes the argument about whose insurer pays when damage straddles the old house and the new build, which is precisely where most disputes happen. Prioritise that single point of contact before you prioritise price.
— Gareth
Need help preparing your insurance-ready paperwork?
Sorting out contract values, certificates, and timescales for your insurer shouldn’t be a second job on top of planning your extension. Complete-Property-Solutions provides fixed-price quotations with a clear contract value from day one, along with prompt contractor liability certificates and realistic project timescales, everything your insurer or broker will ask to see before agreeing specialist cover.
Whether you’re planning a wraparound extension, a garage conversion, or a full structural alteration across Warrington, St Helens, Wigan, Great Sankey, Penketh, Culcheth, Lowton, Rainhill, or Haydock, getting the paperwork right from the outset makes the insurance conversation far more straightforward. Get in touch to discuss your house extension project and we’ll make sure you have everything ready to hand your insurer before work begins.
This article is general information, not a substitute for advice from a qualified financial advisor. Consult a qualified financial professional about your own circumstances before acting on anything here.
Sources
- Home improvements you must tell your insurer | Aviva
- Renovation and extension insurance | Hiscox
- Will your insurance cover home improvements? | Which?
