| TL;DR: Most standard home insurance policies exclude or restrict cover during significant building work, and failing to tell your insurer about a planned extension can invalidate a claim entirely. Depending on the scale of the work, your existing insurer may add cover for a fee, or you may need a specialist renovation policy. Last reviewed July 2026 |
| INSURANCE : HOME INSURANCE DURING BUILDING WORK |
Standard home insurance policies commonly exclude or significantly restrict cover once a property undergoes significant building work, since this changes the risk profile of the property in ways the original policy did not account for. Insurers generally need to be told about a planned extension, and depending on the scale of the project, either your existing insurer can add cover through an endorsement, or a separate specialist renovation policy may be required.
KEY FACTS
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Why standard home insurance often does not cover building work
A standard home insurance policy is priced and underwritten based on the property as it exists at the time the policy is taken out or renewed, assuming normal, settled residential use. Significant building work introduces risks the original policy was never designed to cover, including an open structure more vulnerable to weather damage, materials and tools stored on site that could be stolen, and increased risk of accidental damage during construction activity itself.
Because of this changed risk profile, many standard policies specifically exclude cover for damage arising during, or connected to, significant building work, and some go further, restricting or voiding cover for the whole property during the works period if the insurer was not told about the project in advance.
Why you must tell your insurer, and what happens if you do not
Insurers generally treat significant planned building work as a material change of circumstances that must be disclosed, since it directly affects the risk they are insuring. This is not a minor administrative formality: failing to disclose planned building work can allow an insurer to reject a claim entirely, even one seemingly unrelated to the building work itself, on the basis that the policy was taken out or renewed based on inaccurate information about the property's circumstances.
This means the financial consequence of not telling your insurer is not simply a reduced payout if something goes wrong; in the more serious cases, it can mean no payout at all, leaving you to cover the full cost of a loss that would otherwise have been insured, which is a considerably higher stake than many homeowners realise when they view notifying the insurer as an optional or minor step.
Endorsement versus a separate specialist policy
For a relatively modest, lower-risk extension, such as a single-storey rear extension using conventional building methods, many existing insurers are willing to simply extend the current policy to cover the building work, often through what is called an endorsement, for an additional premium reflecting the temporary increase in risk. This keeps your cover under a single policy and provider throughout the project.
| Type of project | Likely insurance route | Why |
| Small single-storey extension, standard build method | Existing insurer endorsement, for a fee | Lower risk change to existing policy is often manageable |
| Loft conversion with standard structural work | Existing insurer endorsement or specialist policy, depending on scope | Depends on structural complexity and insurer's specific criteria |
| Basement dig or work affecting load-bearing walls | Specialist renovation or structural alterations policy | Higher risk, often outside standard insurer appetite |
| Full property renovation alongside an extension | Specialist renovation policy | Scale and combined risk generally exceeds standard policy scope |
Why the contractor's insurance is not a substitute for your own
A reputable building contractor should hold their own public liability insurance, covering their responsibility for injury or damage to third parties arising from their work, and often their own tools and equipment. This is a separate and additional layer of protection to your own home insurance, not a replacement for it, since your contractor's policy is designed to protect against claims arising from their negligence or activity, not to insure your property, its existing structure, or your contents against the wider range of risks a building project can introduce.
Confirming your contractor holds appropriate liability insurance, and ideally seeing evidence of this before work begins, remains a sensible precaution alongside, not instead of, ensuring your own home insurance properly covers the project.
What a specialist renovation policy typically adds
A specialist renovation or structural alterations policy is generally designed to cover the specific risks a significant building project introduces, including damage to the existing structure during works, theft of materials or fixtures from an active site, and sometimes public liability cover for the homeowner themselves in connection with the works, alongside continuing to cover the underlying building and contents in a way tailored to a property undergoing active construction.
Because these policies are specifically underwritten for higher-risk projects, they generally cost more than a standard home insurance policy or a simple endorsement, but this additional cost reflects genuinely different risk exposure during a larger or more structurally significant project, rather than being an unnecessary upsell for a modest extension that an existing insurer would have been willing to cover through a simple endorsement instead.
What to do once the building work is finished
Once building work completes, it is important to notify your insurer again, both to remove any temporary building-work-specific terms or premium loading that applied during the project, and to ensure your ongoing cover reflects the property's new rebuild cost, which will typically have increased given the additional square footage and improvements the extension has added.
Failing to update your insurer after the work completes can leave a property genuinely under-insured relative to its actual rebuild cost, which in the event of a significant future claim, such as a fire affecting the whole property, could mean a payout that falls well short of what would actually be needed to rebuild the extended property, even though premiums have continued to be paid throughout.
Why timing your notification matters
Notifying your insurer as soon as building work is genuinely being planned, rather than waiting until work has already started, gives the insurer time to properly assess the project and confirm cover terms before any risk period begins, avoiding a situation where work starts before cover arrangements have actually been finalised and confirmed in writing.
Why neighbouring properties can also be affected
Significant building work, particularly excavation or work close to a shared boundary, can occasionally cause damage to a neighbouring property, which is a separate liability risk from damage to your own home and is generally addressed through your own or your contractor's public liability cover rather than standard buildings insurance. Confirming this specific liability is adequately covered before work begins, particularly for a project close to a boundary, avoids a dispute with a neighbour becoming a coverage gap as well as a relationship problem.
| Note: Insurer policies on building work, endorsement availability and specialist renovation cover vary between providers and depend on the specific scope of your project. Always confirm your position directly with your insurer or broker before work begins. |
| RELATED GUIDES |
| Disclaimer: Kael Tripton Ltd is an independent editorial publisher, ICO-registered (ZC135439). This guide is general information, not financial, tax, legal or insurance advice, and carries no commission or referral arrangement. Your circumstances may differ; consider speaking to a regulated adviser before acting. Figures and thresholds change; verify current numbers with the primary sources listed below. |
Frequently asked questions
Do I have to tell my insurer about a planned extension?
Yes. Significant building work is generally treated as a material change of circumstances that must be disclosed, and failing to do so can invalidate a claim entirely.
Can my existing insurer just cover my extension?
Often yes for smaller, lower-risk projects, through an endorsement for an additional fee. Larger or structurally complex projects may need a separate specialist renovation policy.
Does my builder's insurance cover my property during the work?
No. Your contractor's public liability insurance covers their own responsibility for injury or damage they cause, not your property or contents, which remain your responsibility to insure.
Do I need to update my insurance after the extension is finished?
Yes. Notify your insurer once work completes so your ongoing cover reflects the property's increased rebuild cost, avoiding being under-insured going forward.
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