How to challenge a judicial expert report: Practical guide with real examples

By Aurelio Tamarit Blay — Real Estate, Construction and Naval Judicial Expert | Identification No.: 0161

Have you received an expert report in a judicial procedure and do you consider that it contains errors, omissions or unfounded conclusions?Challenging an expert report is a key procedural rightthat can change the course of your case.

In this article, as a judicial expert with more than 30 years of experience in construction, real estate and naval fields, I explainwhen, how and for what reasons you can challenge an expert opinion, with practical examples and references to the Civil Procedure Law (LEC).

⚖️ What is the challenge of an expert report?

The challenge is the procedural act through which a party questions the validity, foundation or conclusions of aexpert reportpresented by the counterparty or even by an expert appointed by the court.

It is not about “disagreeing”, but aboutprove formal or substantial defectsthat affect the reliability of the opinion.

🔍 7 valid reasons to challenge an expert report

1️⃣ Lack of qualification or accreditation of the expert

The expert must beofficially recognizedfor the matter object of the opinion (art. 335 LEC).
✅Example:An architect issues a report on the assessment of boats without accredited nautical training → reason for challenge.

2️⃣ Formal defects in the opinion

• Absence of signature, date or identification of the expert
• Lack of exposure of methodology or sources used
• Omission of the oath or promise of objective action formula (art. 339 LEC)

3️⃣ Incorrect or unproven methodology

If the expert applies technical criteria not accepted by the scientific or professional community, the report loses validity.
✅Example:Housing appraisal using obsolete coefficients not updated to the local market.

4️⃣ Internal contradictions or with documentary evidence

When the conclusions do not logically follow from the data analyzed, or contradict documents provided to the procedure (deeds, licenses, previous technical reports).

5️⃣ Lack of impartiality or conflict of interest

The expert must act with neutrality. If there is a work, family or economic relationship with one of the parties, it is cause for recusal (art. 219 LEC).

6️⃣ Omission of relevant facts

If the report ignores key elements of the case (e.g., dampness not visible during the visit but documented in previous reports), it can be challenged as incomplete.

7️⃣ Speculative conclusion or without technical basis

Conclusions must be derived from objective analyses. Phrases like“in my opinion” or "probably"Without technical support they weaken the opinion.

📅 Procedural deadlines to challenge (LEC)

⚠️Important:Deadlines are fatal. If it is not challenged in a timely manner, the report is deemed accepted.

🛠️ Practical strategy: How to structure your challenge brief

1. Header: Court, procedure number, parties
2. Statement of facts: Objective summary of the contested report
3. Grounds for challenge: Numbered, with reference to legal articles and evidence
4. Application: Request the total/partial rejection of the report or the practice of a new expert
5. Annexes: Documentation that supports your arguments (photos, previous reports, regulations)

✅Pro tip:Accompany your challenge with acontrast reportissued by an independent expert. This technically strengthens your claims.

🎯 Real case: Challenge due to omission of pathologies in housing

Situation: In a procedure for hidden defects, the defendant's expert omitted structural cracks documented in a previous report from the homeowners' association.
Action: A challenge was presented stating:

• Omission of relevant facts (art. 339 LEC)
• Contradiction with documentary evidence provided
• Lack of complete eye visit
  Result: The court admitted the challenge and ordered a new joint expert opinion.

❓ Frequently asked questions

Can I challenge an expert report if it was signed by a court-appointed expert?

Yes. The judicial appointment does not grant immutability to the ruling. They can be challenged on the same grounds as any other report.

Do I need a lawyer to challenge?

Yes. The challenge is a procedural act that must be presented through a solicitor and with legal advice.

How much does it cost to challenge an expert report?

It depends on the complexity. Includes fees for a lawyer, solicitor and, where appropriate, a contrast expert. As a reference, a technical contrast report can range between €800 and €2,500 depending on the subject.

✅ Challenge as a strategic tool

Challenging an expert report is not an exceptional remedy: it is alegitimate procedural toolto guarantee that the expert evidence meets the requirements of objectivity, methodology and substantiation required by law.

Remember: The key is not in “attacking” the expert, but indemonstrate technical or formal defectsthat affect the validity of the opinion.

If you need advice on the viability of challenging a report in your specific case,Contact for a preliminary evaluation without obligation.