An expert witness report is not a technical memorandum with a signature block attached. It is a formal instrument, addressed to a tribunal, that must be capable of standing on its own — surviving written questions, expert conferencing, and cross-examination without the expert needing to fill gaps orally that should have been closed on the page. This piece sets out the structural and content requirements a defensible construction or engineering expert report should meet, and how the IBA Rules on the Taking of Evidence in International Arbitration shape those expectations.
Who the report is actually for
A recurring and avoidable error is drafting a report that reads as though it is addressed to the instructing party's legal team, rather than to the tribunal. The report should generally be addressed to the tribunal itself, written on the assumption that the reader has no prior familiarity with the case narrative and needs to be taken through the technical reasoning from first principles. This has a practical consequence for tone: reports that read as persuasive advocacy, rather than as a considered technical opinion, tend to lose credibility with exactly the audience they need to convince.
The core structural elements
A well-constructed report addresses, at minimum:
- Qualifications and relevant experience, set out with the case-specific expertise in the body of the report and a fuller curriculum vitae attached as an appendix — proportionate to the complexity of the dispute rather than a boilerplate biography
- The substance of instructions received, whether written or oral, so the tribunal can see the brief the expert was working to
- The scope of the opinion, including an honest statement of any questions that fall outside the expert's expertise
- Methodology, stated explicitly wherever tests, calculations, or analytical techniques of a technical nature have been used — including who carried them out and under what supervision
- Material facts and assumptions, with a clear distinction between facts within the expert's own knowledge, facts the expert has been instructed to assume, and facts the expert believes to be true based on the documentary record
- Reasoning, connecting the facts and assumptions to the conclusion in a way a non-specialist reader can follow
- A summary of conclusions, positioned at the end of the report so the tribunal's key takeaways are unambiguous
The IBA Rules' influence on international arbitration practice
Where the IBA Rules on the Taking of Evidence apply — as they frequently do, whether formally adopted or used as informal guidance by tribunals and counsel across DIAC and other regional institutions — Article 5 sets out specific content requirements for party-appointed expert reports. These broadly track the structural elements above but add particular emphasis on:
- A description of the instructions pursuant to which the expert is providing opinions and conclusions
- A statement of the expert's independence from the parties, their legal advisors, and the tribunal
- An affirmation of genuinely held opinions
- Identification of the documents and other information relied upon, in a form allowing the tribunal and other party to identify them
Even in proceedings where the IBA Rules do not formally apply, tribunals experienced in international construction disputes tend to expect reports that meet this standard as a matter of course. Falling short of it does not necessarily render a report inadmissible, but it does invite exactly the kind of procedural challenge and credibility erosion that a well-structured report avoids.
Distinguishing fact, assumption, and opinion — a discipline that runs through the whole document
One requirement deserves particular emphasis because it is where reports most often go wrong: the report must keep fact and opinion clearly separate throughout, not just in a preliminary section. Where there is a range of professional opinion on a matter the report addresses, the report should summarise that range and its sources, and give reasons for preferring the expert's own conclusion rather than simply asserting it. Where material facts are genuinely in dispute, the expert should address each competing hypothesis on its own terms, rather than assuming the instructing party's version and building the analysis exclusively on that foundation.
This discipline is explored further in Part 8 of this series, which looks specifically at fact-versus-opinion pitfalls in delay and quantum reports — an area where even experienced experts routinely stumble.
The statement of truth and declaration
Whatever the governing procedural framework, a construction or engineering expert report should close with a formal verification — a statement of truth confirming which facts are within the expert's own knowledge, and a declaration confirming compliance with the expert's duty to the tribunal, absence of conflicts, and (where relevant) confirmation that no conditional or success-based fee arrangement is in place. This is not a formality to be treated lightly. It is the point at which the expert formally puts their professional standing behind the document, and tribunals and cross-examining counsel treat it accordingly.
Why structure is a credibility issue, not just a style preference
A report that is well organised, transparent about its assumptions, and honest about the limits of the expert's opinion is not merely easier to read — it is measurably harder to attack. Cross-examining counsel look first for the gaps: the unstated assumption, the fact quietly omitted, the methodology never explained. A report constructed with the discipline set out here closes those gaps before the hearing begins, which is the only point at which closing them actually helps.
Part 8 examines one of the most common report-drafting pitfalls in more depth: the failure to keep fact and opinion properly separated in delay and quantum analysis.