Reading a tender specification is not the same as interpreting it correctly. A bidder who simply scans the text without understanding the legal layers underneath misses exactly the places where money or exclusion is at stake: the hierarchy between documents, the status of a Q&A forum answer, the duty to flag omissions, the equivalence clause. This article sets out the Belgian and European rules of interpretation — with the case-law that draws the boundaries — and translates them into a workable guide for bidders.
The standard of interpretation: what does “reading correctly” mean?
The Court of Justice of the European Union set the European benchmark in 2001 in SIAC Construction (C-19/00): award criteria and procurement document clauses must be formulated such that “all reasonably well-informed and normally diligent tenderers can interpret them in the same way”. This benchmark — the reasonably well-informed, normally diligent tenderer — has been the yardstick in every procedure ever since, in Belgium too.
In practice this means two things. First, the contracting authority is responsible for clear documents. Hidden requirements that appear nowhere in the tender specification cannot lead to exclusion — the Pippo Pizzo (C-27/15) ruling is unbending on this point. If an obligation flows solely from national legislation and is not expressly stated in the tender specification, a bidder cannot be held against it.
But there is also a duty on the other side. The bidder must meet the bar of the “reasonably well-informed” reader. Contradictions visible to everyone, ambiguities easily resolved through the Q&A forum — leaving these unaddressed forfeits the right to invoke them later. The eVigilo (C-538/13) ruling refines this: where ambiguities or conflicts of interest are established, the contracting authority bears an active duty to intervene, and in that context the burden of proof can shift to the contracting authority.
Hierarchy of procurement documents — which prevails?
Every sizable tender specification contains contradictions between documents. A quantity in the bill of quantities differs from the plan; the administrative section says something different from a technical chapter; an information notice overrules an earlier clause. Which document wins?
For works contracts, Article 80 of the Royal Decree of 18 April 2017 provides an explicit priority order, unless the procurement documents provide otherwise:
| Level | Document | Note |
|---|---|---|
| 1 | Plans | Prevail over all other documents in case of contradiction |
| 2 | Tender specification (administrative + technical) | Prevails over the bill of quantities |
| 3 | Bill of quantities / inventory | Binding for quantities, but yields to (1) and (2) |
This is the opposite of what many bidders intuitively assume. A plan showing a particular execution prevails over a text describing something else. A bidder who prices solely on the bill of quantities without analysing and recalculating the plans risks that a later “variance finding” will not generate any extra payment but simply fall within the original price.
Two important nuances. First, the contracting authority may include a priority order of its own in the tender specification that departs from Article 80 — this is the case with standard tender books such as SB 250 for road works, which makes the bill of quantities prevail over the tender specification for standardised items. Second, the Belgian Council of State does not always apply Article 80 strictly. Where strict application would lead to unworkable or illogical outcomes, the case-law selects the interpretation that “makes a practical, evident application of the procurement documents possible” (settled case-law, including Council of State of 30 November 2011, no. 216.153). For a bidder: always read the priority clause specific to your tender before falling back on Article 80.
For supplies and services, the hierarchy is less strictly codified, but the same logic applies: the most specific and most formal source prevails. The tender specification prevails over a functional programme or a preliminary study. An information notice prevails over the original version of the tender specification. Oral or bilateral answers do not bind the contracting authority — only written communication through the official channel (e-Procurement Q&A forum) counts.
Contra proferentem — more myth than rule
A common misconception in practitioner literature: “an ambiguous tender specification is automatically interpreted in the bidder’s favour”. That is rarely true without qualification. The Belgian Council of State combines this principle — contra proferentem, the rule that documents are interpreted against the party that drafted them — with an active duty of care on the bidder’s side.
The line emerging from recent case-law: ambiguity only plays in your favour where you show that you could not reasonably have read it differently and that you raised the ambiguity in good time. According to a Tender Law analysis of a Belgian Council of State ruling of May 2023, the case-law qualifies the traditional principle that a bidder is solely responsible for ambiguities in their own bid: the contracting authority also bears a duty of care, for instance to seek clarification on a suspected abnormally low price before concluding to irregularity (Article 66 §3 of the Public Procurement Act of 17 June 2016). Conversely, this means that a bidder who left the ambiguity standing without asking loses the argument later.
In concrete terms: if you raise a question through the Q&A forum before the deadline, your position is strong. If you swallow the ambiguity and build your bid silently on top of it, the Council of State will hold that you have not met the standard of the “reasonably well-informed bidder”.
Binding vs. non-binding communication
Not every document circulating during the procedure carries the same legal weight. The distinction determines whether you may build your bid on it.
Binding
- The tender specification and its annexes as published on the official platform.
- Corrigenda: formally amend the tender specification and are binding on all bidders. Often involve an extension of the submission deadline.
- Q&A forum replies where the tender specification provides that they “form an integral part of the procurement documents” — which is almost always the case in practice. According to a published analysis of a recent Belgian Council of State ruling (late 2025), a forum reply in principle counts as clarification and binds all bidders, without the need for a separate corrigendum.
Non-binding
- Oral replies during an information session or a site visit, unless subsequently confirmed in writing via the forum. A contracting authority that “commits to something” in conversation is itself violating the transparency principle if it does not communicate it to everyone at the same time.
- Bilateral emails between a single bidder and the contracting authority. These breach equal treatment and may not underpin a bid.
- Earlier draft versions of the tender specification that may have circulated by accident.
The grey zone
What if a Q&A forum reply alters an essential clause — for instance, adjusts a selection criterion, expands the scope of the contract, or affects the submission deadline? A forum reply is then no longer legally sufficient. The contracting authority must issue a formal corrigendum, also on TED if the contract is above the EU threshold. Failing to do so risks annulment of the award.
Omissions, errors and presumed quantities
A specific interpretation issue in works contracts: the tender specification contains an omission (a necessary item is missing) or a presumed quantity differs from reality. The Royal Decree of 18 April 2017 governs both situations — in different articles.
Presumed quantities — Article 79 §2, 2°. A bidder may correct a presumed quantity only where the procurement documents expressly allow it. The proposed correction must amount to at least 10 % more or less than the original item. A bidder who alters quantities outside these rules risks having the bid declared non-responsive.
Errors and omissions — Articles 80 to 82 (chapter “Interpretation, errors and omissions”). When you spot an error or omission that makes price calculation or bid comparison impossible, you must report it to the contracting authority without delay and in writing. If the omission concerns a performance not covered by any item of the bill of quantities, the framework of Article 80 still allows the item to be added — again only via a reasoned note submitted with the bid.
Recent Belgian case-law (see the analysis by GD&A Advocaten) also qualifies the principle that every deviation from a technical requirement automatically renders a bid irregular: the contracting authority must expressly indicate which requirements are “minimum” or “substantial”. What the tender specification does not qualify as substantial cannot be used afterwards as grounds for rejection.
A bidder who omits the reasoned note or misjudges the burden of proof risks having the bid declared non-responsive — a substantial irregularity (see also our article on common irregularities in tenders).
”Or equivalent” — assessing the burden of proof
Article 53 §4 of the Public Procurement Act of 17 June 2016 (transposing Article 42(4) of Directive 2014/24/EU) in principle prohibits contracting authorities from prescribing a specific brand, manufacturer or type. Where it is nevertheless done — for instance to describe a specific functionality — the wording “or equivalent” must follow. This is not an empty formula: it is the legal invitation to bidders to propose alternatives.
A bidder invoking the equivalence clause must submit three things with the bid:
- An explicit mention in the bid that an equivalent product is offered, identifying the alternative.
- Technical substantiation — a fact sheet, reference to a standard (NBN, EN, ISO), performance measurement or certificate — demonstrating that the alternative offers at least equivalent value on every relevant characteristic.
- Timely submission — the evidence must be submitted together with the bid. Demonstrating equivalence afterwards is no longer possible.
The case-law of the Court of Justice is strict on this point. In Max Havelaar (C-368/10), the Court confirms that a label cannot be required as such; only the underlying specifications count, and any equivalent proof must be accepted. But the burden of proof rests entirely with the bidder: a bid without an equivalence dossier for the proposed alternative always runs the practical risk of exclusion.
Recent changes affecting your interpretation (2023–2026)
Belgian public procurement law has evolved on several fronts over the past three years. Reading a tender specification as if it were 2020 leads to wrong assumptions about deadlines, price revision and payment.
A single 30-day handling period (from 1 January 2025)
The Royal Decree of 14 August 2024 amended the General Implementation Rules. The earlier split between a verification period (30 days) and a payment period (30 days) has been replaced by a single 30-day handling period for contracts published from 1 January 2025. For care institutions, an exception allows up to 90 days.
In practice: for a tender specification that still refers to the old periods, check whether the procedure falls before or after this cut-off. For anyone publishing after 1 January 2025, a clause “60 days from invoice” is generally contrary to the law.
Performance bond — relaxed regime since 1 November 2023
The Royal Decree of 4 September 2023 relaxed the performance bond regime. Below an award value of €50,000 no performance bond is required. The contracting authority no longer has to justify departures from the standard 5 % rate separately. In each tender specification, therefore, read explicitly:
- Is a performance bond actually required?
- What percentage applies (3 % for framework agreements, often 5 % for the rest)?
- How is release organised (half on provisional acceptance, half on final acceptance)?
SME access — advances and bid compensation (Act of 22 December 2023)
The Act of 22 December 2023, brought into force in stages between January and June 2024, introduced mandatory advances (Articles 12/1 to 12/8 of the Act of 17 June 2016), the possibility of a bid compensation (Article 12/9), the “only once” principle, and transparent rankings below the EU thresholds. For bidders, the key takeaways are:
- For contracts with a long preparation time or substantial bid costs, a bid compensation may be provided — read the administrative section.
- The “only once” principle means that documents the contracting authority can retrieve via Telemarc need not be resubmitted.
Conflicts of interest — circular of 11 June 2024
Since 1 October 2024, the BOSA circular of 11 June 2024 replaces the earlier circulars from 2010 and 2014. Contracting authorities are including standard clauses around “revolving door” situations (former civil servants now working for a bidder). A bidder with such a profile in their team should read this clause twice.
A practical guide: interpret a tender specification in six layers
An experienced bid manager does not go through a tender specification sequentially but in layers. A workable approach:
Layer 1 — Scope and classification. What is the subject matter? CPV codes? Type of contract (works, supplies, services, or mix)? Lots? Duration and possible renewals? A bidder who is not certain that the scope fits their profile does not read further.
Layer 2 — Access. Which exclusion grounds and selection criteria apply? Which proof documents does the tender require (ESPD, attestations, references, classification)? When in doubt: see the article on selection criteria — a misplaced criterion may give you grounds for suspension later.
Layer 3 — Award system. Lowest price, most economically advantageous tender (MEAT), or life-cycle cost? What weighting? Which sub-criteria or appraisal elements? Ask yourself whether the weighting is realistic given your cost structure.
Layer 4 — Quantities and plans. For works contracts: lay the bill of quantities alongside the plans and the technical specification. Mark the discrepancies. Apply Article 80 of the Royal Decree of 18 April 2017: in case of contradiction, plans prevail, then the tender specification, then the bill of quantities. Note presumed quantities (Article 79) and omissions or errors (Articles 80–82) for a possible reasoned note.
Layer 5 — Contractual clauses. Performance bond, price revision, payment term (30 days or transitional regime?), penalties (typically 0.1 % per day, capped at 7.5 %), modifications during performance, dispute resolution. Read these in conjunction with the General Implementation Rules (Royal Decree of 14 January 2013) — what the tender specification does not regulate falls under the General Implementation Rules.
Layer 6 — Deadlines and questions. Submit your questions through the forum before the deadline. Track every information notice and corrigendum. Preserve your rights through a formal notification where you suspect an unlawful clause — the standstill period is 15 calendar days from the reasoned notification.
Common interpretation errors
Blindly trusting the bill of quantities. Contracting authorities forget items. A bidder who does not lay the bill of quantities alongside the plans misses the omission — and can no longer invoke it later.
“Logically” filling in an ambiguous clause. Personal interpretation without confirmation through the forum is risky. Under the SIAC standard, only what all reasonably well-informed bidders can read in the same way counts — not your reading.
Missing corrigenda. The submission deadline was extended, a selection criterion adjusted, an item in the bill of quantities corrected. A bidder following only the original tender specification is bidding on outdated information.
Failing to activate the equivalence clause. When a brand is prescribed and you offer an alternative, an equivalence dossier is mandatory. No dossier = no equivalence = irregular bid.
Posting forum questions only in the final week. Contracting authorities are not required to answer late questions. A bidder who waits too long is stuck with their interpretation and forfeits the ability to invoke the ambiguity afterwards.
Building an oral commitment into your bid. What is “just said” during a site visit does not bind the contracting authority unless confirmed via the forum. Ask the contracting authority expressly to place the confirmation in writing on the forum.
When in doubt: structured questions or preserving your rights
Facing an interpretation problem, a bidder has in principle two instruments: the forum and the standstill period.
Before the submission deadline: asking questions via the forum is the right channel. It is free, fast, and the answers are visible to all bidders — an ambiguity you flag can be resolved for everyone. Ask your question concretely and in legal terms (“Which document prevails in case of contradiction between plan X and item Y in the bill of quantities?”) — not vaguely (“Is the bill of quantities correct?”).
After the award decision: if you believe the tender specification or award rests on an unlawful interpretation, you must file an extreme-urgency suspension application with the Belgian Council of State within the standstill period of 15 calendar days. The period runs from the reasoned notification (Article 4 of the Act of 17 June 2013 on legal protection). If the reasoning is incomplete or missing, request a written addition — the period only starts running meaningfully once you have received a full reasoning. Afterwards an annulment action remains possible within 60 days, but without suspensive effect — the contract may already be performed while you litigate.
For the legal framework, see our article on legal remedies in public procurement.
Conclusion — interpretation is a methodical exercise
A tender specification is not a text to be skimmed. It is a layered legal document where every line plays a role in the comparison with your competitors and in your eventual contractual relationship afterwards. The European transparency standard (SIAC, Pippo Pizzo) and the Belgian duty of care (recent Belgian Council of State case-law) impose one requirement together: read actively, ask systematically, document where your assumptions come from, and preserve your rights within the legal deadlines.
Sources
- Belgian Public Procurement Act of 17 June 2016 — BOSA
- Royal Decree of 18 April 2017 (placement, classical sectors), inter alia Articles 53, 79, 80–82 — BOSA
- Act of 22 December 2023 (SME access) — Belgian Official Gazette
- Directive 2014/24/EU — EUR-Lex
- CJEU, SIAC Construction (C-19/00) — EUR-Lex
- CJEU, Pippo Pizzo (C-27/15) — EUR-Lex
- CJEU, Manova (C-336/12) — EUR-Lex
- CJEU, eVigilo (C-538/13) — EUR-Lex
- CJEU, Max Havelaar (C-368/10) — EUR-Lex
- BOSA — Circular of 11 June 2024 on conflicts of interest
- Schoups — Changes to the Belgian Public Procurement and Concessions Act
- Embuild Antwerp — Navigating errors and omissions
- Rasschaert Lawyers — A forum reply is not a tender specification amendment (Belgian Council of State no. 265.104, 8 December 2025)
- Tender Law — Qualification of the bidder’s duty of care (Belgian Council of State no. 256.528, 15 May 2023)