CPR Part 35: what a construction expert's report must contain

The overriding duty comes first

Everything in Part 35 follows from one rule. It is the duty of an expert to help the court on matters within their expertise, and that duty overrides any obligation to the person who instructed or is paying them (CPR 35.3). A report that reads like an extension of one side's case, however well informed, will be given less weight, and can expose the expert to criticism in the judgment.

In construction and surveying disputes this matters because the expert is often asked about things that are partly technical and partly contractual: whether work was defective, what it would reasonably cost to put right, or what a contract administrator should have certified. The expert's job is to answer the technical and valuation questions clearly, identify where the answer depends on how a contract or the facts are interpreted, and leave the legal questions to the court.

What the report must include

Practice Direction 35 sets out the form and content of an expert's report. In practical terms, a compliant report on a building dispute will:

• Be addressed to the court, not to the party who instructed the expert.
• Give the expert's qualifications and relevant experience, proportionate to the issues. For a quantum report, that means experience of measuring and valuing the type of work in question, not a general CV.
• State the substance of all material instructions, written or oral (CPR 35.10(3)). Those instructions are not privileged once relied on, so they should be recorded with care.
• Set out the facts and assumptions relied on, and make clear which facts are within the expert's own knowledge, such as what was seen on site, and which come from documents or other people.
• Say who carried out any tests, measurements or investigations, and whether they were under the expert's supervision.
• Summarise the range of opinion where there is one, and explain why the expert's view sits where it does.
• Give a summary of conclusions.
• Say whether any opinion is qualified, for example because records are missing or opening-up has not been done, and what would be needed to give a final view.
• Include a statement that the expert understands and has complied with their duty to the court (CPR 35.10(2)) and is aware of the requirements of Part 35, the Practice Direction and the Civil Justice Council Guidance for the instruction of experts in civil claims.
• End with the statement of truth in the exact wording of PD35 paragraph 3.3, including the sentence on contempt of court added in 2020.

The statement of truth

The wording is fixed, and an out-of-date version still turns up surprisingly often. The current form is:

I confirm that I have made clear which facts and matters referred to in this report are within my own knowledge and which are not. Those that are within my own knowledge I confirm to be true. The opinions I have expressed represent my true and complete professional opinions on the matters to which they refer. I understand that proceedings for contempt of court may be brought against anyone who makes, or causes to be made, a false statement in a document verified by a statement of truth without an honest belief in its truth.

What RICS adds for surveyors

Chartered surveyors must also comply with the RICS professional standard Surveyors acting as expert witnesses. The 5th edition was published in July 2026 and takes effect on 30 November 2026. Among other things, it requires the surveyor to:

• disclose any conflict of interest in the report, including financial dependence on a repeat instructing party;
• give a set of RICS declarations at the end of the report, alongside the court's statement of truth;
• avoid pre-populated report templates, so each report is written for the case in hand;
• disclose the use of artificial intelligence or similar tools, and any work done by others;
• give a range of opinion where one exists;
• give separate opinions where the answer depends on which version of disputed facts is accepted.

Where the court's rules or directions in a case ask for something different, the expert follows those.

Common faults that reduce a report's weight

• Advocacy. Adjectives such as "clearly" and "obviously", and a report that deals only with the points that help one side.
• Straying into law. Deciding whether a notice was valid or whether a party was in breach, rather than giving the technical or valuation opinion and showing how it changes if the legal answer goes the other way.
• Unsupported figures. Remedial costs taken from one contractor's quotation without a measured scope, or rates with no source.
• Hidden assumptions. For example, assuming a particular specification applied without saying so.
• Facts and opinion mixed together. The reader should always be able to tell what the expert saw from what the expert concluded.
• No range. Quantum and remedial cost opinions nearly always have a range. A single figure with no discussion of alternatives invites cross-examination.

Questions, joint statements and single joint experts

After reports are exchanged, a party may put written questions to the other side's expert, normally once and within 28 days of service, to clarify the report (CPR 35.6). The court will often direct the experts to discuss the issues and produce a joint statement of what they agree and disagree on, with reasons (CPR 35.12). In lower-value claims the court may direct a single joint expert instructed by both parties (CPR 35.7 and 35.8). The same duties apply, and the expert must treat both parties equally.

How Baker Accordia prepares reports

Our expert witness reports are prepared to CPR Part 35, Practice Direction 35, the Civil Justice Council Guidance and the RICS standard. Each report sets out the instructions, the facts and their sources, the method, the range of opinion and the reasons, and uses measured quantities and sourced rates for any cost opinion. We are happy to review draft letters of instruction before a report is commissioned. Contact us to discuss a matter.

This article is general information, not legal advice. Instructing solicitors should check the current rules and any directions in the case.

This article is general information for professionals and the public, not legal or professional advice, and does not create a client relationship. The law and procedure described are those of England and Wales as understood at the date of publication. Take advice on your own facts before acting.