Lump Sum Contract and Additional Works: When Judges Reclassify Works as New Construction

Imagine for a moment: you are the owner of a small building in Saverne. You sign a lump sum contract with a contractor for renovation works. The works start, and very quickly, the contractor tells you that the main structure needs to be modified – beams to be reinforced, a floor to be redone. You agree verbally, thinking that the lump sum covers the essentials. But at the end, the contractor demands a sum much higher than the agreed price. What to do?

This is exactly the question the Court of Cassation decided in 1982. The case opposed a project owner to a contractor who had carried out much heavier works than planned. The problem: no written addendum had been signed. The contractor invoked Article 1793 of the Civil Code, which requires a written document for any modification of a lump sum contract, and demanded payment for the additional works. But the Court of Appeal, upheld by the Court of Cassation, considered that these works – major adaptations of the main structure – were not mere improvements, but a genuine new construction.

This decision is a valuable weapon for owners. It means that if a contractor far exceeds the initial scope, he cannot hide behind the lack of writing to demand payment. But be careful, everything depends on the nature of the works. Let us decipher together what this 1982 judgment actually changes for you.

The facts: a story that happens every day

In 1973, a property owner in Bischheim entrusts a contractor with carrying out works in a building. The contract is a lump sum contract: a global and final price for precisely described services. But during the works, structural unforeseen events arise. The contractor has to adapt the main structure: load-bearing walls are modified, foundations reinforced. These very substantial works were not included in the initial contract. The project owner accepts them without any written formality – a simple oral agreement, he believes, is enough.

At the end of the works, the contractor presents a bill much higher than the lump sum. The owner refuses to pay the excess, arguing that everything was included in the agreed price. The contractor sues him. At first instance, the court rules in his favour: Article 1793 of the Civil Code imposes a written document for any modification, yet nothing was signed. The owner is therefore obliged to pay.

But the Court of Appeal of Strasbourg reverses this judgment. It considers that the works carried out are not mere improvements, but a profound transformation of the building – a "construction" within the meaning of the law. Consequently, Article 1793 does not apply, and the lack of writing does not block the contractor's claim. The case goes up to the Court of Cassation, which validates the reasoning of the Strasbourg judges.

The reasoning of the court — dissected

The Court of Cassation, in its judgment of 15 December 1982, examines Article 1793 of the Civil Code. This provision states that, in a lump sum contract, any modification must be the subject of a written document signed by the project owner, on pain of nullity. In other words, if you agree orally to additional works, the contractor cannot claim payment for them. But this article has a limit: it only applies to "building contracts", i.e. contracts relating to construction, repair or improvement works on a building.

The Court of Appeal had considered that the disputed works – modifications to the main structure – went beyond the scope of mere improvements. It reclassified them as "new construction", even though they were carried out in an existing building. Why? Because the scale of the interventions (modification of the load-bearing structure, adaptation of foundations) changed the very nature of the structure. The Court of Cassation approves this reasoning: it is a sovereign assessment by the trial judges.

This decision is a confirmation of previous case law. It does not create a reversal, but it clarifies the qualification criteria: the importance of the works, their impact on the main structure, and the fact that they are not mere embellishments. For contractors, this is a warning: do not rely on the lack of writing to invoice colossal works. For owners, it is a protection: if the contractor radically modifies your property without an addendum, you are not obliged to pay the excess.

What this changes for you — concretely

If you are a landlord owner in Saverne, this decision directly concerns you. Imagine you entrust a tradesman with the renovation of a flat for €50,000. During the works, he discovers that the walls are fragile and must consolidate them for an additional €20,000. Without a written addendum, he cannot claim this sum if the works are classified as mere improvements. On the other hand, if the consolidation modifies the load-bearing structure and doubles the living area, the judges could see it as a new construction – and the contractor could then demand payment, even without writing.

For a tenant in Bischheim, the impact is indirect. If your landlord carries out works without an addendum, you could face disputes that delay the works or affect your comfort. But as a third party, you are not a party to the contract.

For a buyer, be vigilant: if you buy a property that has been subject to additional works without an addendum, check that everything is in order. A contractor could come back years later to claim a supplement, especially if the works are classified as new construction (the limitation period is 10 years).

Finally, for a co-owner, this case law can work both ways. If the management company carries out works on the common parts without an addendum, and these works are very substantial, each co-owner could be required to pay their share, despite the lack of writing. It is therefore crucial to formalise any agreement.

Four tips to avoid this type of dispute

• Demand a written addendum for any additional works: even for a minor modification, have a document signed detailing the nature, cost and deadline of the works. This avoids any dispute.
• Have a detailed specification drawn up before signing the contract: describe each service, including any necessary adaptations. The more precise the contract, the less room there is for unforeseen events.
• Photograph and film the condition of the premises before works: in case of a dispute, this visual evidence helps demonstrate the scale of the modifications and their necessity.
• Consult a specialist lawyer before accepting additional works: a professional will help you assess whether the works amount to mere improvements or new construction, and to secure your agreement.

Further reading: related case law and developments

This 1982 decision is part of a line of judgments that define the contours of Article 1793. For example, a judgment of the Court of Cassation of 10 May 1989 (No. 87-10.123) held that works to raise the height of a building constituted new construction, even if carried out under a lump sum contract. Conversely, a judgment of 13 March 1991 (No. 89-16.456) considered that replacing old pipes remained a mere improvement, subject to the writing requirement.

The trend of the judges is clear: they analyse the scale of the works on a case-by-case basis. The heavier they are and the more they modify the structure, the more likely they are to be reclassified. Since 1982, case law has not fundamentally evolved, but judges have become more demanding regarding proof of the importance of the works. For the future, it is likely that the courts will continue to distinguish according to the technical nature of the interventions.

What you absolutely must remember

FAQ:

• Q: Can I refuse to pay for additional works that are not in writing? A: Yes, if the works are mere improvements. No, if they are classified as new construction by a judge.
• Q: What should I do if my contractor demands a supplement without an addendum? A: Do not pay without consulting a lawyer. Ask him to prove that the works were necessary and that they constitute new construction.
• Q: What is the time limit to challenge an invoice for additional works? A: Generally, 5 years from the invoice, but the limitation period may be 10 years if the works fall under the decennial liability.
• Q: Is an oral agreement valid for additional works? A: In law, no, if the initial contract is a lump sum contract. But in practice, if the works are carried out and accepted without reservation, the judge may consider them a valid modification.
• Q: How to prove that works are new construction? A: Through experts, photos, plans, and by demonstrating that the main structure has been modified.

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