The basis: the agreement and article 9
The architect's budget obligation rests on two sources that complement each other. The first is contractual: the agreement concluded with the client, which the Grand-Ducal Regulation of 17 June 1992 laying down the code of conduct for architects and consulting engineers (règlement grand-ducal déterminant la déontologie des architectes et des ingénieurs-conseils) requires in writing, signed by both parties, at the latest once the assignment has been defined (art. 8).
The second is a matter of professional conduct. Article 9 of the same regulation provides that the architect and the consulting engineer "shall take care to submit designs that remain within the limits of the brief set in the assignment and of the budget arising from it, in accordance with the agreement concluded between the parties. Any significant change to the brief set in the agreement, occurring during the design or the execution of the works, must be the subject of an additional agreement stating its financial impact." (unofficial translation)
The text therefore links three elements: the brief, the budget "arising from it", and the agreement. A budget that is written down nowhere, or a brief that has changed without an additional agreement, makes the comparison difficult. What to write into the agreement is detailed in the article on writing the budget into the architect's agreement.
No tolerance percentage
No Luxembourg case law setting an accepted margin of overrun had been identified on the date of verification. In the sources read, there is therefore no threshold above which the architect would automatically be at fault, nor below which the architect would automatically be covered.
Tolerance percentages sometimes quoted in other countries do not carry over. They come from other texts, other practices and other courts. In Luxembourg, the architect's liability for an overrun is assessed case by case, in the light of what the agreement provided, the precision of the design phase and the origin of the gap.
What makes the difference in that assessment is the paperwork. A written budget, a price date, successive estimates kept on file, costed additional agreements: these are the useful evidence, and they are built up before the dispute, not during it.
What strengthens and what weakens the client
| Situation | Effect on the client's position | Why |
|---|---|---|
| Budget costed, dated and defined (works only or total cost) in the agreement | strengthens | the article 9 reference can be identified |
| Changes to the brief formalised in a costed additional agreement | strengthens | the gap due to the brief is separated from the gap due to the design |
| Written response to each estimate, with reservations | strengthens | the client did not accept the drift in silence |
| Budget announced orally or only in an informal exchange | weakens | the limit of the brief and the budget can be disputed |
| Changes requested in meetings, with nothing in writing and no costing | weakens | the gap may be attributed to the client |
| Unreserved approval of a phase already above budget | weakens | it may be read as acceptance of the new amount |
First, identify the gap
Before reacting, the client needs to know where the gap comes from. Three origins call for three different responses.
The gap comes from the brief. The client has added floor area, raised a level of finish, asked for a piece of equipment. If these changes are significant, article 9 required an additional agreement stating their financial impact. Its absence may be held against the architect under the code of conduct, but it does not erase the fact that the change was requested.
The gap comes from the design. With the brief unchanged, the design produces a building that costs more than the budget: circulation areas, structural complexity, technical choices. This is the case article 9 targets directly.
The gap comes from prices or the date. The estimate has been updated to a more recent date than the budget, or the prices used have been revised. This is neither a choice about the brief nor a design failing; the figures must then be compared at the same date before drawing conclusions. An independent counter-estimate helps separate these three parts when the figures are disputed.
The scale of responses
The responses run from the simplest to the heaviest, and each prepares the next.
| Step | Purpose | Form | Timing |
|---|---|---|---|
| 1. Request for adjustment | return within budget with the brief unchanged | letter or email recalling the budget in the agreement and article 9, and asking for costed proposals | as soon as the estimate is known |
| 2. Written trade-off | choose between adjusting the design and changing the brief | trade-off note, then an additional agreement if the brief changes | before the next phase |
| 3. Formal notice | record the failing and set a deadline | registered letter setting out the documents | if adjustment is refused or insufficient |
| 4. Legal action | have liability and its consequences decided | proceedings, with all the written documents | as a last resort |
The request for adjustment is almost always the right first step. Article 9 refers to designs that "remain within the limits" of the budget: asking the architect to return within those limits, with the brief unchanged, is the most direct reading of the text. The expected reply is a list of costed measures, not a general assurance.
The trade-off is the client's decision. If the proposed measures affect the brief, it is for the client to decide, and the decision must leave a written record that will serve as the basis for the additional agreement.
Legal action requires documents. This is where the value of the records gathered at the earlier steps becomes clear. The possible consequences (redoing the design work, reduced fees, damages, termination of the contract) depend on the agreement, the general rules of contract law and the court's assessment.
Before handover, after handover
A budget overrun is not a defect in the building. The architect's budget liability arises during design and construction, on the basis of the agreement and article 9.
The guarantees after handover fall under a different regime. Article 1792 of the Civil Code concerns the loss of the building through a construction defect and makes architects, contractors and other persons bound "to the maître de l'ouvrage" (the client) by a contract for works liable for 10 years; article 2270 distinguishes major works from minor works. These regimes are covered in the article on liability after handover, and insurance in the one on insurance and liability of the parties involved.
In a public contract
For a contracting authority (pouvoir adjudicateur), an overrun by the architect has one more consequence: the budget is often a voted ceiling. In a municipality, the municipal council approves the detailed final design, and "any subsequent significant departure from the detailed final design must be approved by the municipal council and the supervisory authority" (implementing Grand-Ducal Regulation of 8 April 2018, art. 147).
The request for adjustment must therefore come before approval, not after. Once the design has been approved and the tender launched, the estimate becomes the contracting authority's devis (estimate), and the room for manoeuvre shrinks sharply.
What is better avoided
Three common reactions weaken the client. Approving the phase "so as not to lose time" while promising to revisit the budget later. Asking for savings orally, without setting a target amount or a deadline. Changing the brief while complaining about the overrun, without separating the two in writing. The choice of the advisers who help the client document the gap (consulting engineer, cost consultant, project manager) and their respective responsibilities are presented in the article on the architect, the consulting engineer, the cost consultant and the project manager.
This article sets out the rules as they stood on the date of verification and is intended as professional guidance. It does not replace legal advice or an examination of the specific case.