Four roles, one decision
| Participant | Role on cost | Basis | What they answer for |
|---|---|---|---|
| Client | sets the budget, signs the contracts, approves changes | its position as contracting party | its decisions and its cooperation |
| Architect | designs within the budget, assists in choosing the contractor, supervises execution | Act of 20 February 1939; 2022 code of ethics | its appointment, an obligation of means assessed case by case |
| Métreur or économiste de la construction (quantity surveyor or construction cost consultant) | prices, checks quantities and prices | services contract | the assignment described in its contract |
| Project manager or maître d'ouvrage délégué (delegated client) | organises, coordinates, prepares decisions | services contract | the assignment described in its contract |
The client decides
The client is the one who orders the works. Homegrade's brochure "Maîtriser son chantier" (Brussels-Capital Region) defines it simply: the maître d'ouvrage "is the one who orders the works, that is to say you" (unofficial translation, as are all quotations of Belgian texts in this article). The client sets the budget, chooses the contractors, signs the contracts and pays.
The client approves every change. In a private lump-sum contract, article 1793 of the old Civil Code rules out any price increase for changes that have not been "authorised in writing, and the price agreed with the owner". The signature that authorises an extra is the client's.
The client also appoints certain required participants, such as the EPB-verslaggever (energy performance reporter) in Flanders or the health and safety coordinator, required as soon as several contractors are involved. For a structure of less than 500 m², however, that coordinator is appointed by the designer and then by the party in charge of supervising execution. Their role and cost are presented in the article on other required participants.
The architect designs within the budget and supervises execution
The architect's involvement is mandatory for the plans and the supervision of execution of works subject to a building permit, subject to exemptions (Act of 20 February 1939, art. 4), and the profession is incompatible with that of contractor (art. 6). That guarantees independence, not accurate figures.
The budget is part of the appointment. The code of ethics of the Order of Architects of 16 November 2022 requires the architect to design "within the limits of the programme set in the appointment and of the budget", and to price any change to the programme in a convention additionnelle (additional agreement) stating its financial impact (art. 16). The architect assists the client in choosing the contractor "on the best terms of price and quality" (art. 22). The agreement is in writing at the latest once the appointment has been defined (art. 20): that is where the budget must appear. How it fits with the contractor's contract is covered in architect and works contracts.
The quantity surveyor prices and checks
One occupation, several job titles. Le Forem describes the métreur under the titles of économiste de la construction, métreur-vérificateur or métreur-deviseur, and states that there is no statutory requirement to practise the occupation. The contract defines the assignment: estimate, counter-estimate, checking a bill of quantities or interim valuations.
The quantity surveyor neither designs nor supervises execution, tasks reserved to the architect. The figure is only as good as the documents and price date used.
The project manager organises
Homegrade speaks of a maître d'ouvrage délégué when the client entrusts part of its organising role to a third party. That third party prepares decisions, coordinates and follows programme and budget, but the function has no legal status of its own: its contract defines it.
The project manager does not decide in the client's place. Without a precise written mandate, the project manager signs neither contracts nor extras, and contractors must know it.
Who signs what
The one who prices is not the one who decides. The architect or quantity surveyor prices a change, the project manager presents its effect on budget and programme, the client signs. A change approved orally, or by someone without a mandate, invites a dispute over price.
The articles in this branch
- The article on the architect, the quantity surveyor and the project manager covers each one's assignment, contract, guarantees and independence. Their professional liability insurance is presented there.
- The article on what changes in 2027 with Book 7 of the Civil Code covers the two states of private contract law. A table compares the current rules with those for contracts concluded from 1 September 2027.
This article sets out the rules as at 21 October 2026 and is intended for professional orientation. It does not replace legal advice or the assessment of the individual case.