Expert Witness Evidence in Building Defects Claims

In a building defects claim, the court rarely decides who is right by looking at photographs and listening to the parties argue. It decides on the strength of independent technical evidence. An expert witness in a building defects case is the chartered surveyor or engineer who examines the work, measures it against the standard that applied at the time, explains what went wrong and why, and puts a defensible figure on the cost of putting it right. This guide explains what that evidence must establish, when it is needed, how it is prepared under CPR Part 35, and what it typically costs in England and Wales.

What does an expert witness prove in a building defects claim?

Whether the claim is brought in contract, in negligence or under the Defective Premises Act 1972, the claimant has to prove the same three things, and each one is a technical question before it is a legal one:

• Breach of the standard. The work fell below what was required. That standard may be the contract specification and drawings, the Building Regulations 2010 and Approved Documents, a British Standard, a manufacturer's installation instructions, a warranty provider's technical requirements, or simply the reasonable care and skill implied by section 49 of the Consumer Rights Act 2015.
• Causation. The breach caused the damage complained of, rather than poor maintenance, a later alteration, an inherent feature of the building or a separate contractor's work. Causation is where defects claims are most often won and lost.
• Quantum. The reasonable cost of remedial works, plus any consequential loss such as alternative accommodation or loss of rent, supported by a costed schedule rather than a builder's estimate.

An expert witness report on building defects is structured around those three questions. Anything that does not help the court answer them is noise, and a good expert leaves it out.

When is expert evidence needed?

Not every defect dispute needs a full court-compliant report. On the small claims track (claims under £10,000) the court will often manage with a concise specific defect report and photographs. Once a claim is allocated to the fast track, intermediate track or multi-track, or goes before the Technology and Construction Court, expert evidence will almost always be directed, and the court will decide whether each side may call its own expert or whether a single joint expert should be appointed.

Expert input is also valuable long before proceedings are issued. The Pre-Action Protocol for Construction and Engineering Disputes expects the letter of claim to set out the defects alleged, the basis of the claim and the sums sought. A letter of claim backed by an independent technical opinion is far harder to brush aside than one built on the homeowner's own description, and many disputes settle at this stage. Homeowners weighing up their options can read whether you can sue a builder for poor workmanship and when to hire an expert witness for construction defects for the timing decision in more detail.

Typical defects that reach litigation

The panel's construction expert witness surveyors and engineers are instructed across the full range of residential and commercial building failures. The defects that most commonly end up in a formal claim include:

• Water ingress through roofs, flat roof coverings, balconies, parapets and render, and the associated damp and timber decay.
• Structural movement caused by inadequate foundations, unsupported openings or removed load-bearing walls, which may call for a structural engineer's report alongside the building surveyor's evidence.
• Extensions, loft conversions and basements built without Building Regulations approval or in breach of the approved drawings.
• New-build defects: poor workmanship discovered after completion, incomplete snagging, and disputes with warranty providers.
• Defective external wall systems, cladding and fire-stopping in flats, and failed tanking or basement waterproofing installations.

How the expert inspects and reports

The starting point is a site inspection, usually with the defects still in place. Once remedial work has been carried out, the expert can only work from photographs and third-party accounts, and the evidence weakens considerably. Where safety allows, the defect should therefore be inspected before it is repaired. The inspection is typically non-destructive, but opening-up works, moisture readings, level surveys, drainage CCTV and laboratory testing may be recommended where the cause cannot otherwise be established. Where both parties have experts, joint inspections are common and save cost.

The report itself must comply with CPR Part 35 and Practice Direction 35. The expert's overriding duty is to the court, not to the party paying the fee, and the report must set out the expert's qualifications, the documents and facts relied on, the range of opinion where one exists, the reasons for the conclusions reached, and the statement of truth. What a compliant report looks like is covered in more depth in what a CPR Part 35 expert witness report contains. Chartered surveyors on the panel also work to the RICS practice statement Surveyors acting as expert witnesses, which is mandatory for RICS members.

After exchange of reports, the court will usually order the experts to meet and produce a joint statement identifying what they agree and disagree on, and each side may put written questions to the other's expert under CPR 35.6. Only the issues that remain in dispute go to trial, where the expert may be cross-examined.

Time limits that shape a defects claim

Limitation is a technical point that catches many claimants out, and the expert's chronology of when the defect arose and when it was discoverable is often central to it. Under the Limitation Act 1980 a claim for breach of a simple contract must be brought within six years of the breach, or twelve years where the contract was executed as a deed. Claims in negligence run six years from the damage, subject to a three-year extension from the date of knowledge under section 14A. For dwellings, the Building Safety Act 2022 extended the limitation period for claims under section 1 of the Defective Premises Act 1972 to 15 years for work completed after 28 June 2022, and to 30 years retrospectively for work completed before that date. Which of these applies is a matter for your solicitor, but it will determine how far back the expert's investigation needs to look.

What does a building defects expert witness cost?

Fees are driven by the size of the property, the number and complexity of the defects, the volume of documents and whether court attendance is likely. As a guide, and consistent with the figures in the panel's expert witness cost guide, a CPR Part 35 report on a straightforward residential defects matter typically falls between £5,000 and £15,000. Complex multi-defect disputes, large commercial buildings or cases involving several disciplines can run to £20,000 to £50,000 or more. Hourly rates for chartered surveyors and engineers acting as experts are generally £150 to £300, with court attendance charged at around £1,000 to £2,000 per day. Where a single joint expert is appointed, the fee is normally shared equally between the parties. Most experts will provide a fixed fee for the initial inspection and report so that the cost is known before the instruction is confirmed.

Instruct a building defects expert witness through Survey Merchant

Survey Merchant provides RICS chartered surveyors and structural engineers from a national panel of 2,400+ professionals to act as expert witnesses in building defects claims across England, Wales, Scotland and Northern Ireland. The discipline is matched to the dispute, whether that is building pathology, structural engineering, housing disrepair, dilapidations or surveyor negligence, and fixed fees are quoted before any instruction is confirmed. Solicitors, homeowners, landlords and management companies can review the construction expert witness service, send the details of the dispute through the contact page, or call 0204 579 8270 to discuss an appointment and receive an expert CV and fee quote.