Building Insurance and Warranties for London Extensions
Insurance during and after a building project is often an afterthought — until something goes wrong. Understanding what coverage you need at each stage protects your property, your investment, and your legal position.
Site Insurance During Construction
Standard home building insurance typically excludes or limits cover for building works in progress. Before any work starts:
Notify your home insurer: Tell your insurer you are undertaking building works. Failure to notify can invalidate your existing policy if a claim arises from the works.
Contract Works Insurance: Covers the building works themselves — materials on site, work in progress, contractor equipment. Usually the contractor provides this as part of their service. Confirm with your contractor before assuming it's in place.
Public Liability Insurance: Covers third-party injury or property damage arising from the building works. A reputable contractor carries at least £2m (ideally £5m or £10m) public liability insurance as a standard. Ask for a certificate before work starts.
Employer's Liability Insurance: If you hire any labour directly (rather than through a contractor), employer's liability insurance is a legal requirement.
What Your Contractor Should Hold
Before signing a contract or allowing work to start, obtain copies of:
- Public liability insurance certificate (minimum £2m, ideally £5m)
- Employer's liability insurance certificate
- Confirmation that contract works/all-risks insurance is in place
A contractor who cannot provide these should not be starting work.
After Completion: Home Insurance Update
After the works are complete, notify your home insurer of the increase in property value and floor area. Failure to update your policy after a significant extension means you may be underinsured if you suffer a loss.
Structural Warranties (Latent Defects Insurance)
A structural warranty (also known as latent defects insurance) provides coverage for inherent structural defects that emerge in the years after completion. Standard policies provide 10 years of cover.
Structural warranties are:
- Required by most mortgage lenders for new-build properties
- Increasingly common for self-build projects
- Less commonly taken out for extensions, but available
Providers include NHBC, Premier Guarantee, Build-Zone, and others.
Building Regulations Compliance and Insurance
A Completion Certificate from Building Control is evidence that the works comply with Building Regulations. Insurers and future buyers place value on this — works completed without Building Regulations compliance can be a significant issue when selling.
RCB Design & Build
RCB Design & Build carries full public liability and employer's liability insurance as principal contractor — and can advise on contract works insurance, completion certificates, and post-completion insurance notifications.