Building Safety Act Claims: What Expert Evidence Is Needed

A Building Safety Act expert witness is a chartered surveyor, fire engineer or structural engineer who gives independent opinion evidence on whether a building contains a “relevant defect”, how it arose, who is responsible and what it will reasonably cost to put right. The Building Safety Act 2022 created new remedies for leaseholders, building owners and regulators, and almost every one of them turns on technical questions a court or tribunal cannot decide without an expert. This guide explains the main routes to a claim, what the expert must establish on each, which disciplines are needed and what the evidence costs.

Which claims does the Building Safety Act create?

Four routes account for most of the litigation in which surveyors give evidence.

• Remediation orders (section 123). The First-tier Tribunal (Property Chamber) can order a landlord to remedy relevant defects in a “relevant building” by a set date. A relevant building is, broadly, a self-contained building of at least 11 metres or five storeys containing at least two dwellings.
• Remediation contribution orders (section 124). The tribunal can order a landlord, the original developer, or a company associated with either, to pay towards the cost of remedying relevant defects where it is just and equitable to do so. This is how leaseholders and freeholders recover money from those responsible rather than simply forcing the works.
• Building liability orders (section 130). The High Court can extend a company’s liability for a building safety matter to its associated companies, so a claim is not defeated because the development vehicle has no assets.
• Extended limitation (section 135). Claims under section 1 of the Defective Premises Act 1972, for dwellings that were not fit for habitation when completed, can now be brought up to 30 years after completion for work finished before 28 June 2022, and 15 years for later work. A new section 2A of the 1972 Act covers refurbishment work on existing dwellings from the same date.

Cladding is the best-known subject, covered in the guide to expert evidence in cladding and EWS1 disputes, but the same provisions apply to missing cavity barriers, defective fire doors and compartmentation, inadequate structural fire protection and any other work that creates a building safety risk. For the regulatory side of the Act, including the higher-risk building regime and the gateways, see the September 2026 Building Safety Act update.

What is a relevant defect, and what must the expert prove?

Under section 120, a relevant defect is one arising from works done in the 30 years before 28 June 2022, or from later works, that causes a building safety risk: a risk to the safety of people in or about the building arising from the spread of fire or the collapse of the building or any part of it. Three consequences follow for the expert.

First, the defect must be identified physically, not inferred from paperwork: as-built drawings and building control records are the starting point, but intrusive opening-up at representative locations is normally needed to confirm what was installed. Second, the risk must be characterised. A non-compliant detail with no material effect on fire spread or structural stability may be a breach of the Building Regulations, but it is not a relevant defect, and the tribunal will expect the expert to say so. Third, the dating matters: the works must fall within the statutory window, and compliance is judged against the Approved Documents in force when the works were approved, not today’s requirements.

Expert evidence for remediation and contribution orders

For a remediation order the tribunal needs evidence that a relevant defect exists, that it creates a building safety risk, what works are required and how long they will reasonably take.

For a remediation contribution order the focus shifts to money: the costs already incurred and those still to come, whether each item was reasonable and properly attributable to the relevant defect, and how responsibility should be apportioned between the developer, the contractor and the current landlord.

The First-tier Tribunal is not bound by the Civil Procedure Rules, but its directions on expert evidence typically mirror CPR Part 35: an overriding duty to the tribunal, a statement of truth, disclosure of instructions and a joint statement where each side has its own expert. Each party normally bears its own costs in the tribunal save for unreasonable conduct, so the expert fee should be budgeted as a cost of the application.

Defective Premises Act claims: proving the dwelling was unfit

The extended limitation period has revived claims against developers, contractors and designers on blocks completed in the 1990s and 2000s. The test under section 1 of the 1972 Act is whether the dwelling was fit for habitation when completed, a higher bar than a breach of the Building Regulations. The expert has to show that the defect, alone or with others, made the dwelling unfit, for example because the external wall or compartmentation would allow fire to spread in a way that prevented safe occupation.

Because the relevant date is completion, often decades ago, the expert must reconstruct the building’s condition at that time from contemporaneous records, opening-up and reasoned inference, separating original defects from later alterations and deterioration. Loss is the reasonable cost of remedial work, less any betterment, or diminution in value where pleaded. These claims are heard in the Technology and Construction Court, where Part 35 applies in full; the wider framework is explained in the guides to expert evidence in building defects claims and suing a builder for poor workmanship.

Which expert discipline does a Building Safety Act claim need?

Most claims need more than one expert. A chartered building surveyor normally leads on what was built, whether it complied with the regulations in force, what defects exist and what remediation will cost. A chartered fire engineer is required where the fire-engineering analysis itself is in dispute. A chartered structural engineer deals with collapse risk and structural fire protection; the panel’s structural engineers are instructed alongside building surveyors on these points. A RICS Registered Valuer addresses diminution in value through valuation expert witness evidence.

How much does Building Safety Act expert evidence cost?

For the panel’s chartered surveyors, hourly rates are typically £150–£300. A report on a straightforward matter, such as a single-block remediation order application or a Defective Premises Act claim about one dwelling, generally falls within £5,000–£15,000. Multi-party TCC claims with extensive opening-up and several rounds of joint statements can reach £20,000–£50,000 or more, and attendance at a hearing or trial is usually charged at £1,000–£2,000 per day. Opening-up works, access equipment and laboratory testing are separate costs. In court the losing party usually pays a proportion of the winner’s reasonable expert fees, subject to the court’s power to limit them under CPR 35.4(4); the guide to who pays expert witness fees covers the recovery rules.

Building Safety Act expert witness services from Survey Merchant

Survey Merchant provides RICS chartered surveyors as construction expert witnesses in Building Safety Act claims, drawn from a national panel of 2,400+ surveyors working to CPR Part 35 and the RICS practice statement Surveyors acting as expert witnesses. The panel’s experts prepare reports for leaseholders, management companies, freeholders, developers, insurers and their solicitors in remediation and contribution order applications, Defective Premises Act claims and related negligence proceedings, and are paired with structural engineers and valuers where needed. Fixed fees are quoted wherever the scope is clear, and single joint expert appointments are accepted. Before a claim is issued, a specific defect report can establish whether a relevant defect is likely to exist, and leasehold advice is available to flat owners facing remediation charges. To discuss a Building Safety Act dispute, contact Survey Merchant or call 0204 579 8270, and the right expert will be matched to the issues in dispute.