What the architect owes on the budget
The obligation is set by the code of ethics, and it is precise. The code of ethics of the Order of Architects of 16 November 2022 requires the architect to submit designs "within the limits of the programme set in the appointment and of the budget" (art. 16, unofficial translation). Any change to the programme "must be the subject of an additional agreement stating its financial impact". The budget is a design limit, and every change of programme is priced in writing in a convention additionnelle (additional agreement).
The architect's role on cost extends to the choice of contractor. The same code asks the architect to assist the client in choosing the contractor "on the best terms of price and quality" (art. 22): the estimate becomes the reference for reading the tenders.
A written budget is worth more than a budget mentioned in passing. The architect's agreement must be in writing at the latest once the appointment has been defined (art. 20): that is the moment to record the amount, its price date and what it includes, as recommended in the guide to the client's construction budget in Belgium.
Independent does not mean accurate
The architect's involvement is mandatory. The act of 20 February 1939 requires the use of an architect to draw up the plans and supervise the execution of works subject to a building permit (art. 4), subject to exemptions. That monopoly is covered in detail in the article on the architect and mandatory involvement.
The profession of architect is also incompatible with that of contractor (art. 6). The architect therefore does not sell the works being estimated.
But independence says nothing about precision. An estimate can be honest and wrong: quantities taken from schematic drawings, prices carried over from an old project, items missing from the drawings (external works, utility connections, building services). The architect answers for the budget under an obligation of means assessed case by case; the client, for their part, pays the difference if they discover it when the tenders are opened.
Checking at each phase, on three points
An estimate is checked by comparing it with the budget and with the previous phase. A comparison only makes sense if three elements are identical.
| Checkpoint | Question to ask | What distorts the comparison |
|---|---|---|
| Quantity base | Are the areas and quantities measured on the same drawings and under the same convention? | A gross area compared with a net area, a partial métré (meetstaat, bill of quantities) |
| Price date | In which month are the prices expressed? | An old budget compared with current prices |
| Items | Are the same items included, excluding VAT (HTVA), with or without external works and fittings? | A "total cost" budget compared with a "works" estimate |
At sketch design stage, the estimate is an order of magnitude: you check that the programme and areas fit within the budget. At preliminary design stage, it is broken down by main items, which shows where the gap is concentrated. At permit application stage, the project is fixed in its broad lines: the last phase at which reducing the programme costs little. At construction documents stage, it rests on a detailed bill of quantities and becomes the reference for judging the tenders.
Ask for the gap, not just the total. At each phase, require a line explaining the change since the previous phase: what comes from a change of programme (which should have been the subject of an additional agreement), from quantities, from prices. An estimate that rises without explanation is a warning sign.
The check can be entrusted to a third party. The métreur (quantity surveyor), whom Le Forem also describes as a construction economist, calculates "the fairest price" and checks the gap between estimate and actual costs. The quantity surveyor does not replace the architect: they document the gap.
In a public contract, the estimate is a legal obligation
The pouvoir adjudicateur (aanbestedende overheid, contracting authority) must estimate the value of the contract. The act of 17 June 2016 on public procurement requires it (art. 16), and its amounts are understood excluding VAT. That estimate determines the procedure and the publication requirements, then serves to compare the tenders: if it is too low, it sets the stage for tenders that exceed it.
The articles in this branch
- The article on when the architect exceeds the budget covers the architect's liability, the trend in published decisions and the steps open to the client.
- The article on the estimate that exceeds the budget before tendering covers diagnosing the gap and the levers to pull, in order. It continues with a method for preparing the trade-off note that documents the decision.
- The article on the independent counter-estimate covers the second estimate prepared by a third party on the same documents.
- The article on the mandatory estimate in a public contract covers what the estimate determines: procedure, publication, comparison of tenders.
This article sets out the rules as at 21 October 2026 and is intended for professional orientation. It replaces neither legal advice nor an examination of the specific case.