Do I need Site Insurance AND a Structural Warranty when converting or extending?

Some Q&As on why it is necessary to choose both Site Insurance & Structural Warranties

Whether you’re planning a major extension or converting a barn, garage or loft into a liveable space, you might be wondering if both Site Insurance and a Structural Warranty are necessary. While many people arrange Extension Insurance or Conversion Insurance for the build phase, a Structural Warranty provides vital long-term protection and is often required by lenders and future buyers.

What is Extension Insurance, Conversion Insurance and Site Insurance?

Site insurance protects your project during construction, from the start of works until completion. It covers risks such as fire, storm damage, theft, malicious damage, public liability and injury claims, as well as loss or damage to plant, tools and materials on site.

At Self-Build Zone, policies can be tailored specifically as:

• Extension Insurance – for homeowners extending an existing property, whether single or multi-storey
• Conversion Insurance – for projects that change the use or structure of an existing building, such as converting a barn or commercial space.

These types of Site Insurance are essential because standard home insurance is unlikely to cover major works or associated liabilities.

Do you also need a Structural Warranty?

A Structural Warranty (sometimes called a 10-12 year warranty or latent defects insurance) provides cover after the project is completed. It protects against defects in design, workmanship or materials that affect the structural integrity or waterproof envelope of the building.

Here’s why it matters:

• Mortgage lender requirement – Most lenders insist on a structural warranty before they’ll release funds for conversion or extension works
• Peace of mind – Covers hidden defects that might only appear years after completion
• Ease of resale – Buyers and solicitors expect to see a warranty certificate when purchasing a home with recent building work
• Avoids legal disputes – Unlike relying on architect certificates, a warranty allows for claims without needing to prove negligence

Site Insurance vs Structural Warranty

Site insurance covers damage during construction, including tools, materials and liability, and should be in place from the day work begins. Extension or Conversion Insurance is a specialist form of Site Insurance designed for alterations to existing buildings and needs to be arranged before any structural work starts. A Structural Warranty, on the other hand, protects against defects in the structure or waterproofing after the project is complete, and provides cover for ten years from the date of completion.

Together, they provide full lifecycle protection, from groundworks to long after you move in.

When should you arrange cover?

• Extension or Conversion Insurance should be in place before any works begin, ideally, once you’ve confirmed your builder and project start date
• A Structural Warranty should be arranged at the start of the project, before key stages like foundation pouring or roofing begin. This ensures site inspections can be carried out and the warranty remains valid.

If you leave it too late, you may need a retrospective warranty, which is often more expensive and may require intrusive inspections or building reports.

How much does it cost?

• Site insurance (including extension or conversion insurance) is typically priced based on build duration and project cost. You can expect to pay a few hundred pounds for small extensions, with prices rising for larger or complex projects
• Structural warranties usually cost around 1% of the total project value. This is a one-time payment and lasts for ten years

Self-Build Zone offers transparent pricing and policies underwritten by ‘A’ Rated insurers, ensuring both peace of mind and lender acceptance.

Final thoughts: Do you really need both?

Yes. Site insurance covers you during the build, protecting your materials, your contractors and any third-party liability. But once the work is complete, only a structural warranty will protect you (and future owners) against serious latent defects.

If you’re investing in your home, make sure that investment is appropriately safeguarded, for now and the future.

Key takeaways

• Arrange Extension or Conversion Insurance before building starts
• Secure a Structural Warranty at the start of the project to ensure full eligibility
• Check that your policy is accepted by UK mortgage lenders and backed by financially strong insurers
• Keep all certificates and documents safe for resale and peace of mind.

Self-Build Zone offers specialist insurance and warranty products for self-builders, renovators and extenders. Get in touch today to protect your home improvement from start to finish.

For tailored advice and quotes from Self-Build Zone, explore the rest of our website or contact our team.

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