You had works carried out on the basis of a quote, a verbal agreement and a few emails. Afterwards, the contractor sends an invoice higher than you expected, or containing works you thought were included in the original agreement. Or you dispute additional works to which you never expressly consented. No formal contract does not mean there is no agreement — but the burden of proof becomes the central issue. And recent case law brings that burden of proof into sharper focus.
Many building owners only discover at the first conflict how fragile their paper trail actually is. A signature on a quote without general terms, a down payment based on an Excel spreadsheet, emails with technical details but no price confirmation. The Court of Cassation clarified on 5 December 2022 that a contracting agreement can be proven by the conduct of the parties, and the Mons Court of Appeal confirmed the marginal price review on 2 June 2022. This article explains which principles strengthen your evidentiary position — or, conversely, how you can anticipate a contractor submitting a questionable invoice.
A contracting agreement is consensual — writing is not a validity requirement
The starting point: a contracting agreement is a consensual contract. It is formed by mutual consent on the work and the price. No signature, no notarial deed, no registered letter required. Anyone claiming otherwise misplaces the writing requirement at the wrong level.
The Court of Cassation recently refined this rule. In its judgment of 5 December 2022 (Cass. AR C.22.0134.N), it confirmed that a contracting agreement can be proven by the conduct of one of the parties. Ordering additional works, performing works, receiving performance without protest: all these behaviours can, under Article 8.31, second paragraph of the Civil Code, qualify as an extrajudicial admission. Such an admission constitutes evidence against the person who made it, unless it is not sincere (Article 8.32 CC).
For you as building owner or contractor, this means: even without a written agreement, you can enforce contractual rights. But conversely, your own conduct can also be used against you — a down payment, a photo report, a site visit, an email discussing results: each bears the mark of implicit consent.
Proof of the price: a separate challenge
The position is different when the price itself is disputed. A contracting agreement is a contract for consideration, of which the price is an essential element. When the price is not fixed, it must be determinable at the time the contract is formed. It is permitted for the contractor to set the price — but the court retains a marginal review power: a contractor may not demand an abnormally high price.
The Mons Court of Appeal ruled on 2 June 2022 (Mons 16th ch. no. 2021/RG/409, JLMB 2023, issue 36, 1608, T.Aann. 2023, issue 2, 225) on a file in which the contractor failed to prove that the client had agreed to his price. No signed quote, no description of the works in the quote or invoices, no price documentation. Moreover, three counter-quotes obtained by the building owner showed that the requested price was not justified. The court reduced the price to a reasonable amount based on Article 1134, paragraph 3 of the old Civil Code (now Article 5.73 CC): good faith prevents a contractor from abusing the absence of a fixed price.
For you as building owner, this is an important finding: even without a written agreement on the price, you can, through marginal review, have an unreasonably high invoice reduced — provided you produce your own documentation (comparative quotes, market prices, price catalogues).
General terms and conditions: only what is proven counts
Many contractors refer to general terms and conditions on their quotes or invoices. The question is whether those terms actually form part of the contract. The answer of the Brussels Court of Appeal (Brussels 4 January 2024, JLMB 2024, issue 27, 1204) is clear: the contractor cannot rely on general terms and conditions of which he does not demonstrate that they form part of the contract between the parties. A quote without a signed copy of the general terms, and without even a reproduction of the clause invoked, is insufficient.
For you this means: a contractor relying on his general terms (for instance to impose a shortened complaint period, to limit liability, or to set conditions for additional works) bears the burden of proving that those terms were made known to you before or upon conclusion of the contract. A reference on the back of an invoice, or a mere mention on a quote without a copy, is generally insufficient.
Proof of defects: a bailiff's report is not enough
The same Brussels judgment of 4 January 2024 adds a second lesson. When you as building owner complain about defects, you must prove them — and for technical issues that is rarely possible without adversarial expert investigation. A bailiff's report is not enough. Nor are poor-quality photos from which the origin of the defects cannot be established.
In practice this means: a file without an expert report is a weak file. For mapping defects after acceptance, see also the spoke on minor hidden defects after acceptance of construction works.
B2C protection: the transparency requirement
When you as a private individual (consumer) contract with a professional contractor, an additional layer of protection applies. Article V.2, 1° and Article VI.37 § 1 of the Code of Economic Law oblige the business to inform you before contract conclusion of the main characteristics of the service — including which performance will be delivered and what costs are involved.
The Antwerp Court of Appeal (Antwerp B2E2e ch. no. 2023/AR/1193, 10 September 2024) applied this rule strictly to an interior architect who combined a fee of 6% on the cost price with an hourly rate during the execution phase, without further specification. The court held that neither clause met the transparency requirement. The architect was required to identify the successive performances and to provide at least an indication of the associated costs. In case of doubt about the meaning of a clause, the interpretation most favourable to the consumer prevails (Article VI.37 § 2 CEL).
For B2C contracting contracts, an imprecise price calculation is therefore not a lack of service but a potential breach of the information obligation — which allows you either to have the clause declared inapplicable or to enforce a more favourable interpretation.
What if the contractor invokes additional works without your written consent?
A common conflict. The contractor carries out "extra" work and invoices it afterwards, without you having expressly agreed in writing. Under the old Article 1793 of the Civil Code, strict formalism applied to fixed-price contracts for the construction of a building: without a written document, any price change was unlawful. The Book 7 draft bill abolishes this article, but the Antwerp Court of Appeal has already tipped the balance in its judgment of 16 April 2024 (Antwerp B2E2e ch. no. 2023/AR/1007, DAOR 2025, issue 153, 20): in the absence of information about additional works, the consumer may assume that all works performed were included in the original agreement. He does not have to pay compensation for additional works.
The legal framework surrounding additional works is complex and evolving rapidly. Also read the spoke on additional works the contractor invoices separately.
Practical: what to do when your evidentiary position is shaky?
A file without a formal contract rarely leads to a quick outcome. But a well-substantiated file does — even after the fact. Collect all email correspondence, text messages, dated photos, payment receipts, witnesses, delivery notes. Ask everyone who was on the site to briefly put their version on paper. Ask a construction expert for an amicable technical report. If in doubt: through a lawyer, request the appointment of a court-appointed expert via a unilateral petition to the president of the court.
For a broader overview of your rights as a building owner, see the pillar on rights and obligations of the building owner in contracting. Do you have a specific file in which the written contract is missing and the discussion is stalled? Reius Advocaten assists individuals and businesses with such evidentiary files. Contact us at info@reius.be for an initial evaluation.