Lump Sum Contract: Can the Contractor Claim an Extra If the Third Party's Study Was Erroneous?

Imagine: you entrust the renovation of your house in Bonifacio to a contractor, based on a quote prepared according to the measurements provided by your architect. The work begins, and then, nasty surprise: the actual quantities are much higher. The contractor asks you for an extra. But you signed a lump sum contract (global and final price). Who must pay? How far does the protection of the lump sum go?

This question is asked by hundreds of owners and contractors each year in Corsica, particularly within the jurisdiction of the Ajaccio Court of Appeal. The answer lies in a decision of the Court of Cassation of 19 January 2017 (no. 15-20.846), which provides crucial clarification: the lump sum nature of the contract does not protect the negligent third party (architect, design office) whose error led to an underestimated quote. The contractor can claim against that third party for compensation for the loss suffered.

This decision is a breath of fresh air for aggrieved contractors, but it also reminds owners that signing a lump sum contract does not shield them from all recourse. Analysis.

The facts: a story that happens every day

La Société Marseillaise du Tunnel (SMT) entrusts to the company Campenon Bernard a works contract for the construction of structures. The price is fixed based on measurements taken by a third party, the project manager. But the actual quantities turn out to be significantly higher. The contractor, bound by a lump sum contract (global and final price), cannot claim any extra from the employer (the client).

What to do? The contractor then turns to the project manager, the design office that made the measurement error, and sues them for liability (claim for damages). The Aix-en-Provence Court of Appeal dismisses the claim, holding that the lump sum nature of the contract exempts the third party from any duty to compensate. The contractor appeals to the Court of Cassation.

The Court of Cassation quashes the appeal judgment: it recalls that the lump sum (fixed and final price) is a clause in the contract between the employer and the contractor. It cannot benefit a third party (the project manager) who committed a fault (the measurement error) causing loss to the contractor. The third party must compensate for that loss, regardless of the lump sum.

The reasoning of the court — explained

The Court of Cassation relies on Article 1240 of the Civil Code (formerly 1382), which provides: "Any act of a person which causes damage to another obliges the person by whose fault it occurred to compensate for it." In plain language: if you make an error and someone else suffers the consequences, you must compensate them.

The judges consider that the lump sum (global fixed price) is an agreement between the employer and the contractor. The latter cannot ask the employer for an extra, even if the actual quantities are greater. On the other hand, that does not prevent the contractor from claiming against the third party (project manager) who provided erroneous measurements, if that error caused his loss (underestimation of the quote).

The decision does not create a new principle: it applies the general law of extra-contractual liability (tort). The project manager is not a party to the construction contract, so the lump sum is not enforceable against him. He must answer for his fault like any third party. This is a confirmation of case law: the lump sum is not a shield for negligent professionals.

The lower court judges (Court of Appeal) erred in holding that the lump sum excluded any compensable loss. The Court of Cassation restores the logic: the loss exists (the contractor worked at a loss), and it is directly linked to the fault of the design office.

What this changes for you — concretely

This decision has direct implications for several players in the construction industry, whether you are in Ajaccio, Bonifacio or elsewhere.

For the contractor

You signed a lump sum contract, but the actual quantities are greater due to a measurement error by the project manager? You cannot claim the extra from the owner, but you can take action against the project manager (architect, design office). Example: in Ajaccio, a contractor built a villa for €250,000 on a quote, but the foundations required 30% more concrete due to an erroneous soil study. He obtained €75,000 in damages from the design office.

For the landlord owner

You are protected by the lump sum: the contractor cannot claim an extra from you, unless you yourself modified the project. But be careful: if you are also the project manager (e.g., you provided the measurements yourself), you could be considered a negligent third party. In that case, the contractor could sue you for liability. An owner in Bonifacio thus had to compensate his contractor to the tune of €15,000 because he underestimated the demolition volume.

For the co-owner

In the context of works in a condominium (rendering, roofing), the condominium association is the employer. If the design office makes an error, the contractor cannot claim an extra from the co-owners, but can claim against the design office. This avoids unexpected calls for funds.

Four tips to avoid this type of dispute

• Check the measurements and preliminary studies. Before signing a lump sum contract, have the quantities checked by an independent professional. A double reading of the plans can avoid costly errors.
• Specify the reference documents in the contract. The quote must clearly mention the plans, calculation notes and measurements on which it is based. In case of error, you will be able to identify the responsible party.
• Ensure that your project manager has professional liability insurance. In case of error on his part, his insurance must cover the damages. Demand a certificate before the start of works.
• Include a revision clause for major unforeseen events. Even in a lump sum contract, it is possible to include a clause allowing the price to be adjusted in case of unforeseeable discoveries (e.g., rock, presence of asbestos). To be negotiated with the owner.

Further reading: related case law and developments

This decision is part of a series of rulings by the Court of Cassation that limit the scope of the lump sum in the face of third-party liability. For example, in a judgment of 3 November 2016 (no. 15-20.847), the Court had already held that the project manager incurs contractual liability towards the employer for a measurement error, but also delictual liability towards the contractor.

Conversely, some earlier decisions had exonerated the project manager on the ground that the contractor had accepted the lump sum with full knowledge. But the current trend is more protective of the contractor, especially when the error is attributable to a professional subject to a heightened duty of care (architect, design office).

For the future, it can be expected that judges will be increasingly attentive to the allocation of responsibilities: the lump sum protects the employer, but not negligent third parties. Real estate professionals must therefore redouble their vigilance in their preliminary studies.

In practice: what to do

1. If you are a contractor and victim of a measurement error: gather the evidence (quote, plans, erroneous measurements, bailiff's reports if necessary). Put the project manager on formal notice to compensate you. If refused, sue him in the tribunal judiciaire. Time limit: 5 years from the discovery of the loss (Article 2224 of the Civil Code).
2. If you are an owner and the contractor asks you for an extra: refuse by invoking the lump sum. If the contractor insists, consult a specialised lawyer. You can also bring proceedings against the project manager so that he assumes his liability.
3. If you are a project manager: take out appropriate insurance and check your measurements. In case of error, try an amicable settlement to avoid a costly trial.

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