Renovation Insurance and Structural Warranties: What Every London Property Owner Needs to Know

A major renovation involves significant financial exposure. Structural work, specialist installations, and prolonged construction activity create risks that standard home insurance does not cover. Getting the insurance and warranty picture right before work starts is not bureaucratic caution — it is basic risk management for a project that may represent a seven-figure investment.

This guide covers the main categories of insurance and warranty protection relevant to a prime London renovation: what they cover, what they do not, who should hold them, and what to check before appointing a contractor.

Site insurance during the works

Standard home insurance does not cover a property during a major renovation. The policy terms of most domestic insurers exclude cover where structural works are being carried out, where the property is unoccupied for an extended period, or where contractors are on site. This is a gap that must be filled before works begin.

Contract Works insurance

Contract Works insurance (also called All Risks insurance) covers the works themselves — materials, plant, and the building under construction — against loss or damage during the construction period. It covers fire, flood, theft, and accidental damage to the works, and is typically maintained until practical completion.

Contract Works insurance can be taken out by either the contractor or the client. The standard practice on larger projects is for the main contractor to hold it, with the client named as an additional insured. The policy limits must be adequate to cover the full rebuild cost of the project.

What to check: Before work starts, confirm in writing who holds the Contract Works policy, that it is active, and that the policy limits are appropriate for the project value. Ask for a copy of the certificate.

Public Liability insurance

Public Liability (PL) insurance covers the contractor's liability for injury to third parties or damage to third-party property caused by the construction activities. In a prime London renovation — where works are often in close proximity to neighbouring properties, public footways, and shared structures — this is essential.

Contractors working on high-value London projects should carry Public Liability cover of at least £5,000,000, and for projects of significant scale or complexity, £10,000,000 is appropriate. The policy must be current throughout the works.

What to check: Ask for the contractor's PL certificate before they start on site. Verify the cover level and the expiry date. A contractor who cannot produce this document should not be on site.

Employers' Liability insurance

If the contractor employs staff — and all legitimate contractors do — they are legally required to hold Employers' Liability insurance. This covers claims from employees who suffer injury or illness in connection with their work.

This is a legal requirement, not a negotiable. Any contractor who cannot produce an Employers' Liability certificate is either operating with employed workers without legal cover (a criminal offence) or using a labour model that creates liability for the client.

Existing structures cover

On renovation projects — as distinct from new builds — the existing structure of the building is a separate risk from the works themselves. Contract Works policies typically cover damage to the existing structure caused by the works, but only if existing structures cover is explicitly included.

This is important on projects involving basement excavation, structural alterations, or any work close to the party wall, where the risk of incidental damage to the existing building is real. Confirm with the contractor that their policy includes existing structures cover before any structural work begins.

Professional Indemnity insurance for design professionals

The architect, structural engineer, and any other design professional involved in the project should hold Professional Indemnity (PI) insurance. This covers claims arising from errors, omissions, or negligence in their professional work — a structural design that fails, a planning application submitted incorrectly, a specification that causes loss.

PI insurance is claims-made, meaning it covers claims made during the period of insurance regardless of when the underlying work was done. The implication is that a design professional who does not maintain their PI policy after completing your project is not covered for claims that arise later.

What to check: Ask for PI certificates from all design professionals before appointment. For a project of significant value, £2,000,000–£5,000,000 of cover is appropriate. Confirm the policy is active and will be maintained for a period after practical completion.

Structural warranties

A structural warranty (sometimes called a latent defects warranty or a building warranty) is a long-term insurance policy — typically 10 years — that covers the cost of repairing structural defects discovered after the construction is complete.

Structural warranties are distinct from the contractor's defects liability period (typically 12 months after practical completion, during which the contractor is obliged to return and remedy defects at their own cost). A warranty covers structural defects that emerge after the defects liability period has expired.

When structural warranties matter most

Structural warranties matter most in three contexts:

New build and conversion: For a project that creates a new dwelling — a basement conversion that adds a new habitable floor, a loft conversion that adds a bedroom — most mortgage lenders require a structural warranty as a condition of lending on the completed property. Without one, the property may be unmortgageable, which affects both the owner's financing options and the future saleability of the property.

Sale: Buyers' solicitors routinely ask for structural warranty documentation on properties that have been significantly extended or converted. Without one, a buyer's solicitor may require a retention from the sale proceeds, or the buyer may decline to proceed.

Peace of mind: For a high-value renovation, a 10-year structural warranty provides assurance that if a structural defect emerges — ground movement, foundation failure, structural cracking — the remediation costs are covered.

Major providers

The principal structural warranty providers in the UK are:

For prime London renovation and conversion projects, Build-Zone, Premier Guarantee, and Checkmate are the most commonly used providers. The warranty provider inspects the works at key stages during construction — foundations, structure, weatherproofing — as a condition of issuing the policy.

Cost: Structural warranty premiums are typically 0.5–1.5% of the build cost, depending on complexity and the provider. On a £1,000,000 renovation, this implies a premium of £5,000–£15,000.

Neighbour protection: the party wall context

For renovations involving party wall works — basement excavations, rear extensions, loft conversions — the Party Wall etc. Act 1996 requires the building owner to serve notice on adjoining owners and, where required, appoint a party wall surveyor.

This is not strictly an insurance matter, but it has insurance implications: the building owner is liable for damage caused to adjoining owners' properties by the works, and that liability must be covered under the contractor's Public Liability and existing structures insurance.

Adjoining owners are entitled to request a Schedule of Condition — a photographic and descriptive record of their property's condition before works begin — which provides the baseline against which any damage claim is assessed. ASAAN prepares and commissions Schedules of Condition as standard practice on all projects involving party wall works.

See our party wall guide for the full procedure.

What a responsible contractor's insurance pack looks like

When appointing a contractor for a significant London renovation, the following insurance documents should be provided before works commence:

1. 1.Contract Works (All Risks) insurance certificate — confirm limits cover full rebuild value
2. 2.Public Liability insurance certificate — minimum £5,000,000; £10,000,000 for complex projects
3. 3.Employers' Liability insurance certificate — legally required; confirm it is current
4. 4.Confirmation that existing structures cover is included in the Contract Works policy

Any contractor who cannot or will not provide these documents should not be appointed, regardless of the price they have quoted. The absence of adequate insurance on a major renovation project is not a minor administrative issue — it is a fundamental risk to the client's investment.

ASAAN carries all required insurance to the levels appropriate for high-value London renovation projects, and provides full insurance documentation as a matter of course at the outset of every project. If you would like to discuss insurance requirements for a proposed project, contact us or read our guide on how to choose a renovation contractor.