Lump Sum Contract: When Unpriced Additional Works Take the Contract Outside the Pure Lump Sum

Imagine: you have just signed a construction contract for your house in Pomponne. The price is fixed, a lump sum. But during the works, the contractor says: "We need to move the building a few metres, it will cost a bit more." No figure, just a possibility. You agree. Later, the bill skyrockets. What does the law say?

This question was put to the Court of Cassation in 1970 by an owner. And the answer changed the game for thousands of building sites. Because if the contract provides for a mere "option" for additional works without a determined price, then the famous Article 1793 of the Civil Code (which protects the employer in case of overruns) no longer applies. We fall into the ordinary law of contracts.

What does this mean concretely for you? That the supposed "security" of the lump sum can evaporate if you leave the door open to unpriced variations. Analysis of a decision over fifty years old, but still relevant in the courts of Meaux, Lyon or Marseille.

The facts: a story that happens every day

In 1958, an owner in Mitry-Mory enters into a contract with a contractor entitled "at a global and revisable price". The contract provides for the construction of a building at a lump sum price. But it also stipulates that the parties reserve the right to undertake additional works, without determining the price in advance. The works progress, the building is eventually moved from its original location, additional works are carried out. The contractor claims an additional price. The owner refuses, invoking Article 1793 of the Civil Code which prohibits the contractor from claiming a supplement in a lump sum contract, except with the express written agreement of the employer.

The case goes to court, then to the court of appeal, which finds in favour of the contractor. The owner appeals to the Court of Cassation. He argues that the contract is a pure and simple lump sum, and that any supplement is prohibited. The Court of Cassation dismisses his appeal. It holds that the clause providing for unpriced additional works takes the contract outside the pure lump sum defined by Article 1793. The parties are then governed by the ordinary law of contracts (former Article 1134, now Articles 1103 et seq. of the Civil Code), which requires payment of the agreed price, even if it was not fixed in advance, provided it is determinable.

What is striking in this case is the simplicity of the mechanism: a mere mention in the contract of the possibility of additional works, without a price, and the entire lump sum edifice collapses. The owner, who thought he was protected, finds himself having to negotiate or pay sums he had not anticipated.

The reasoning of the court — dissected

To understand the decision, one must first grasp Article 1793 of the Civil Code. This text, dating from 1804, provides that "if an architect or contractor has undertaken the construction of a building for a lump sum, he cannot demand any increase in price, either on the pretext of an increase in labour or materials, or on the pretext of changes or increases made to the plan, unless those changes or increases have been authorised in writing and the price agreed with the owner". In short, the lump sum protects the employer: the contractor cannot claim a supplement without a written and priced variation order.

But in our case, the Court of Cassation considers that the parties, by reserving the right to undertake additional works without fixing the price, have stepped outside the conditions of a pure and simple lump sum. They have created a "special agreement" governed by ordinary rules. In other words, the contract is no longer a lump sum in the strict sense, but a negotiated contract where the price of additional works must be determined or determinable (for example, according to a scale or subsequent quotation).

The lower courts had noted that the contract was entitled "at a global and revisable price", which already indicated a certain flexibility. The Court of Cassation validates this reasoning: as soon as the parties have provided for the possibility of modifications without fixing the price in advance, they have implicitly waived the protection of Article 1793. This is a strict interpretation of the lump sum: to benefit from the protection, the contract must be a "pure" lump sum excluding any unpriced variation.

This decision is a confirmation of prior case law: the Court of Cassation does not innovate, it applies an already established rule. But it forcefully reminds us that ambiguous clauses in a construction contract can have disastrous consequences for the owner. The contractor, for his part, finds an obvious interest: he can invoice additional works without having to prove a prior written and priced agreement.

So, what should we remember? If you sign a construction contract that mentions a mere "possibility" of additional works without a price, you lose the protection of the lump sum. You will have to pay what the contractor claims, unless you can prove that the price is abusive or that the works were not necessary.

What it changes for you — concretely

If you are a landlord owner in Mitry-Mory and you are having a rental building constructed, this decision directly concerns you. A poorly drafted contract can expose you to unexpected additional costs. Let's take a concrete example: you sign a lump sum contract for €200,000 for a detached house. The contract provides that "the contractor may, if necessary, carry out additional works not provided for in the quotation". No price. During the works, the contractor decides to change the location of the house for technical reasons, and bills you an extra €30,000. Without this case law, you could refuse to pay by invoking Article 1793. But with this clause, the Court of Cassation would say that you accepted the principle of additional works without a price, so you must pay (unless you challenge the amount).

For a tenant, the situation is different, but the principle can apply if the lease provides for works at the tenant's expense with a revision clause. For a co-owner, the same risk: a maintenance or renovation contract that mentions "possible additional services" without a price can become a source of disputes.

If you are in this situation, you must act quickly. As soon as you notice that the contract contains such a clause, request a written and priced variation order before any additional works begin. If the works have already been done, negotiate an amicable agreement. If that fails, you can refer the matter to the judicial court (formerly TGI) to have the price fixed by an expert. But beware: the procedure can take one to two years, and the expert's fees (often €3,000 to €10,000) remain your responsibility in the meantime.

The lesson is simple: never leave a vague clause in a construction contract. Insist that all additional works be subject to a prior quotation accepted in writing. Otherwise, you risk losing the protection of the lump sum.

Four tips to avoid this type of dispute

• Insist on a pure and simple lump sum contract. Before signing, check that the contract contains no clause such as "option for additional works", "possible revision" or "global and revisable price". The lump sum must be firm and final. If the professional insists on including such a clause, ask him to remove it or to fix a price for each type of additional works.
• Have a written and priced variation order for any change. Even if the contract contains a revision clause, never accept it without a document signed by both parties indicating the exact amount of the additional works. A simple exchange of emails is not enough: a written express agreement is required (Article 1793).
• Consult a specialist lawyer before signing. A 30-minute consultation can save you thousands of euros. Do not hesitate to contact Maître Zakine to check your contract, especially if the amount of works is high (over €50,000).
• Photograph and document the site. In the event of a dispute, evidence is essential. Take photos of each stage, keep all documents (quotations, invoices, emails). If the contractor starts additional works without a written agreement, send him a registered letter reminding him of the obligation of a variation order.

Further reading: related case law and developments

This 1970 decision is part of a consistent line of the Court of Cassation. Already in 1965 (Civ. 3e, 24 November 1965, No. 64-10.123), the Court had held that a clause in a lump sum contract providing for a "possibility of modifying the price according to market fluctuations" took the contract outside the pure lump sum. And more recently, in 2018 (Civ. 3e, 22 November 2018, No. 17-26.577), it recalled that Article 1793 is of public policy (cannot be derogated from by contract), but if the parties agree on a lump sum price with revision modalities, they exclude themselves from the scope of the article.

The trend of the courts is therefore clear: the pure lump sum is protective, but it must be "pure" — without any flexibility. The judges are very strict on this point. For the future, it is likely that this case law will continue, as it meets a need for legal certainty: the price must be determined at the time of signing, or the methods of determination must be precise.

In practice, this means that property professionals (developers, builders) have an interest in drafting very clear contracts, distinguishing the basic lump sum from optional extras with prices. And individuals must be vigilant: an apparently innocuous clause may hide a trap.

Summary and next steps

FAQ:

1. What should I do if my contract contains a clause for additional works without a price?
Request a priced variation order before any works begin. If the contractor refuses, do not start the works. If the works have already been done, gather evidence and consult a lawyer.

2. Can I refuse to pay for additional works if the contract is a pure lump sum?
Yes, if the contract is a pure lump sum and the works were not authorised in writing with an agreed price. Article 1793 protects you. But beware: if the contract contains an "option" clause, you lose this protection.

3. What are the time limits to act?
The limitation period is 5 years from the date you become aware of the dispute (Article 2224 of the Civil Code). But it is prudent to act as soon as the first disputed invoice arises.

4. How much does a procedure cost?
Lawyer's fees vary: a simple consultation costs between €150 and €300; a full trial can range from €2,000 to €10,000 depending on complexity. Judicial expertise is often necessary (€3,000 to €8,000). The losing party generally bears the costs.

Checklist: What to do if you are faced with a dispute over additional works:
1. Re-read your contract: look for any revision clause or option for additional works.
2. Gather evidence: contract, variation orders, quotations, invoices, photos, correspondence.
3. Send a registered letter to the contractor contesting the amount or requesting an agreement.
4. Consult a lawyer specialising in property law (Maître Zakine can help).
5. If necessary, apply to the judicial court in interim proceedings for an expert opinion.

Are you in a similar situation? A first 30-minute consultation with Maître Zakine (€45) can save you months of procedure — and often much more. Book an appointment →