The client's construction budget in Belgium: setting it, checking it, holding it

Each moment has its risk and its lever, and each lever has its source. The last column cites the text the client can rely on.

The first two moments cost little and return the most. Correcting a brief at sketch stage costs only a revision of the drawings; correcting it during the works is paid for in extras and delays.

The budget is an input to the project, not the result of the drawings. A client who asks the architect "what will this cost" once the preliminary design has been drawn has already given up its main lever. A client who sets the envelope first can then require the project to fit within it.

This lever has a precise basis in professional ethics. The code of ethics of the Ordre des architectes of 16 November 2022 requires the architect to submit designs "within the limits of the brief set in the appointment and of the budget" (art. 16, unofficial translation, as are all quotations of Belgian texts in this guide). The same article adds that any change to the brief "must be the subject of an additional agreement stating its financial impact". The budget must still exist, and it must be in writing.

Writing has its moment. The code provides for a written agreement between the architect and the client "at the latest when the appointment has been defined" (art. 20). That agreement is where the budget belongs, with its content and its date. A budget mentioned in a meeting, with no record, carries almost no weight on the day the estimate exceeds it.

The architect's budget is not the project budget. The first covers the works, in principle excluding VAT. The second adds everything the client will pay on top: fees for the architect and engineers, health and safety coordination, the energy performance assignment, insurance, utility connections, planning taxes and charges, VAT, finance costs, contingency and price adjustment.

Several of these items are imposed by law. Health and safety coordination on temporary or mobile construction sites rests on the federal Act of 4 August 1996 and the Royal Decree of 25 January 2001: as soon as several contractors are involved, a coordinator is appointed for the design stage and one for the construction stage (Act, art. 16 and 21). The client appoints them itself for a structure with a total area of 500 m² or more; below that, the designer and then the party in charge of supervising execution do so, in practice the architect where the architect's involvement is compulsory (Royal Decree, art. 4bis, 4decies, 5 and 15). For housing where the involvement of an architect is compulsory, the Act of 31 May 2017 requires ten-year civil liability insurance, the certificate for which is provided before the works begin.

Energy and planning items depend on the region. In the Walloon Region, an approved responsable PEB (energy performance adviser) must be appointed (decree of 28 November 2013), with an initial PEB declaration attached to the permit and a final declaration after the works. In the Flemish Region, the bouwheer appoints an EPB-verslaggever (energy performance reporter) before the works begin. In the Brussels-Capital Region, charges d'urbanisme (planning charges) rest on a government decree of 26 September 2013, and a 2024 reform has been reported; no amount is given here, because it depends on the use, the region and the text in force on the date of the application. VAT, finally, is costed according to the nature of the works and conditions that are checked case by case: this guide gives no rate.

A budget without a value date can be compared with nothing. Construction prices move between the day the budget is set and the day tenders are submitted, and again during the works. Writing "works budget of X euros excluding VAT, value [month and year]" makes it possible to update the figure later instead of finding it already exceeded.

The contingency must be visible, not hidden in the line items. It covers three distinct things: the uncertainty of the estimate, which narrows as the project takes shape; site risks, such as ground conditions or the existing building; and changes to the brief that the client will decide on itself. The only numerical benchmark in this guide comes from a regional body: Homegrade, in the Brussels-Capital Region, recommends a reserve for unforeseen items "of the order of 10% of the works amount" (brochure "Maîtriser son chantier", 2022). This is guidance for the general public, not a standard; the right contingency is justified by identified risks and released stage by stage.

Naming the region is not a detail. The permit (permis d'urbanisme in Wallonia and Brussels, omgevingsvergunning in Flanders), energy requirements and charges differ from one region to another. A budget that does not say where it applies does not say what it contains either. These points are developed in the branch on setting the budget before the drawings.

The architect is compulsory, independent and bound by the budget; none of this makes the estimate accurate. The federal Act of 20 February 1939 requires an architect to prepare the drawings and supervise the execution of works that need a building permit (art. 4), subject to exemptions, and makes the profession incompatible with that of contractor (art. 6). This incompatibility ensures the architect does not also sell the works being estimated. It does not ensure the figure is right.

The 2022 code gives the architect two obligations that are useful to the client. Staying within the budget (art. 16), and assisting the client in choosing the contractor "on the best terms of price and quality" (art. 22). The first gives the client a basis for requiring a design that fits the written budget; the second makes tendering part of the appointment, not a formality.

An estimate is checked by comparison, and comparison requires three constants. The same basis of quantities, the same value date, the same line items. A sketch-stage estimate per square metre and a preliminary-design estimate item by item can only be compared once brought into the same form.

The useful rhythm follows the project stages. Sketch design, preliminary design, permit application file, construction file: at each stage, the client asks for an updated estimate, the variance against the budget, and the cause of the variance. A cause always falls into one of three families: prices (the market has moved), quantities (the project has grown or become more precise), the brief (the client has asked for more). The first two are discussed with the architect; the third calls for a priced additional agreement (art. 16).

The cheapest moment to correct is before tendering. If the estimate exceeds the budget at the end of preliminary design or of the construction file, the effective levers are, in order: the brief and floor areas, the level of finish, options, phasing, the procurement route for the works, and only then prices. Waiting for the tenders to notice the gap means paying for it in retendering time.

A second estimate can document the gap. A counter-estimate prepared by a third party on the same documents, by a métreur or économiste de la construction (quantity surveyor or construction cost consultant: the job titles used by Le Forem, an occupation with no statutory requirement), or by an engineering consultancy, serves to make a disagreement objective. It replaces neither the architect, whose involvement is required by the 1939 Law, nor the architect's liability.

The architect's liability for the budget is an obligation of means, assessed case by case. Published decisions show a trend, not a rule. According to actualitesdroitbelge.be, the civil court of Nivelles (13 February 1995) considered that an overrun of 10% of the initial approximate budget was the maximum acceptable limit, and the Ghent court of appeal (10 November 2006) held a 17% overrun unacceptable. According to Legal News (De Keuster, 2019), the courts of Liège (4 April 1996) and Brussels (18 February 2010) did not accept overruns of 15% and more.

Two limits temper this trend. The Court of Cassation (4 November 2004, cited by actualitesdroitbelge.be) held that ethical obligations do not make the budget an essential element of the contract. According to the same source, an overrun cannot be attributed solely to the architect where the client has not cooperated (Ghent, 10 November 2006). In practice, the client is all the better placed for having written down the budget, dated its requests and recorded its changes to the brief. What the client can do, in order: require the project to be adapted to the budget, give formal written notice, and only as a last resort go to court. These remedies are set out in the article on when the architect exceeds the budget: what the client can do.

The contracting authority must estimate the value of the contract. The Act of 17 June 2016 on public procurement, a federal law applicable in all three regions, says so (art. 16) and specifies that, unless otherwise provided, its amounts are understood excluding VAT. The estimate is not just a management tool: it determines which procedure is available, the advertising, and then how the tenders are read. Underestimating often condemns the authority to tenders that are all above the estimate. These points are developed in the branch on checking the architect's estimate.

Public and private contracts do not offer the same levers at tender stage. A private client is free to negotiate, retender and reduce the scope. A contracting authority is bound by a procedure, but that procedure gives it tools that private clients do not have in so clear a form.

Price verification covers all tenders. The Act of 17 June 2016 provides for price verification (art. 84), and the Royal Decree of 18 April 2017 on award procedures sets the order: correction of errors (art. 34), verification of the prices or costs of all tenders (art. 35), then examination of abnormally low or high prices (art. 36). In the latter case, the contracting authority requests written justification within 12 days, then either rejects the tender or states, in the award decision, its reasons for finding the amount not abnormal; no justification is required for negligible items. An abnormally low tender is a budget risk, not a windfall: it is often recovered through extras or ends in default.

The right not to award is the strongest lever. "Completing a procedure does not entail an obligation to award or conclude the contract" (Act of 17 June 2016, art. 85). The contracting authority may abandon or restart the procedure, "if necessary in a different way", and the decision not to award is published. Restarting only makes sense if what produced the gap is reviewed first: the estimate, the brief or the division of the contract into lots. The options are set out in the article on tenders above the estimate: abandon, negotiate, retender.

Negotiation is not a general right of the contracting authority. It depends on the procedure chosen and therefore, often, on the estimated value. The main cases are shown in the table below, based on the consolidated texts read on 21 October 2026.

Above these levels, the European threshold changes the framework. For works, it stands at 5,404,000 euros (Royal Decree of 18 April 2017, art. 11). The negotiated procedure without prior publication also covers other situations, in particular where no tender or no suitable tender has been received (art. 42, § 1, 1°, c), a notion the law defines and which is not the same as a tender that is merely expensive. This table does not replace checking, for each contract, the exact condition and the version in force.

Private freedom is only useful if tenders are comparable. The client can negotiate, ask for a second tender, invite other firms or reduce the scope. One discipline conditions everything: comparing tenders on the same basis, that is, the same quantities, the same items, the same options and the same date. A lower tender that omits an item is not cheaper; it moves the cost onto the site.

The choice of procurement route weighs on the budget as much as prices do. A main contractor gives one price, coordination included, with a margin on subcontractors. Separate trade packages often give lower unit prices, but coordination, interfaces and omissions stay with the client. The choice also changes the protection regime that applies to housing, which should be checked before tendering. Keeping a written record of each version of each tender makes it possible, later, to explain the gap between the budget and the signed contract. These points are developed in the branch on tendering without losing the budget.

The only figure that matters during the works is the forecast final cost. The contract sum is known; what is not known is what the client will have paid at the end. A useful dashboard fits on one page and is updated at each état d'avancement (interim valuation): initial budget, committed amount, approved extras, extras under discussion, price adjustment, quantity variances, forecast final cost, remaining contingency.

The contingency is consumed, and it must be seen being consumed. Each approved extra, each quantity variance, each price adjustment is charged against it. When the remaining contingency falls below the risks still open, that is the signal to make trade-offs, not at the end of the works.

Article 1793 of the old Civil Code is the private client's most direct lever. Where an architect or contractor has undertaken to build a building for a lump sum, according to a plan settled and agreed with the landowner, they "may not claim any increase in price", whether for a rise in the cost of labour or materials or for changes or additions to the plan, "if those changes or additions have not been authorised in writing, and the price agreed with the owner".

The text therefore sets two cumulative requirements. Written authorisation of the change and an agreed price. For the budget, the practical consequence is simple: no extra is carried out without a written instruction and a price accepted before execution. An extra carried out first and priced afterwards leaves the client negotiating after the event, from a weak position, over work already built into the structure.

Terminating has a cost, which must be provided for. Article 1794 allows the client to terminate the lump-sum contract at will, by compensating the contractor for its expenses, its work and everything it could have earned.

On the architect's side, the same logic applies to changes to the brief. Any change requested by the client goes through an additional agreement stating its financial impact (2022 code, art. 16). The rule protects the client as much as the architect: it forces costing before deciding. The detail is in the article on extras in a private lump-sum contract.

The general implementing rules strictly govern modifications. The Royal Decree of 14 January 2013 (règles générales d'exécution, general implementing rules) provides that modifications are ordered in writing and valued at the unit prices of the tender (art. 80). Additional works (art. 38/1) and modifications due to circumstances that "a diligent contracting authority could not foresee" (art. 38/2) are each limited to 50% of the initial amount per modification. A low-value modification must remain below the European threshold and below 15% of the initial amount for works, in cumulative net value (art. 38/4). Substantial modifications are excluded (art. 38/5 and 38/6).

Quantities and prices also move without any modification. Where the quantities actually carried out for an item exceed three times, or fall below half of, the estimated quantities, either party may request a revision of the unit prices, the revised price applying only beyond three times (art. 81). Price adjustment is compulsory in works contracts, except where the estimated value is below 120,000 euros and the initial period is below 120 working days or 180 calendar days (art. 38/7). A review clause applies where the contractual balance is upset, from a loss of at least 2.5% of the initial amount for works (art. 38/9).

The rhythm of tracking is set by payments. The déclaration de créance (payment claim) and the detailed statement are checked and paid within 30 days (general implementing rules, art. 95). It is at each interim valuation that the dashboard is updated, item by item, projecting the final quantity rather than recording the quantity carried out. These points are developed in the branch on tracking the final cost during the works.

Managing cost is not a single function, but four roles that must not be confused. The client decides; the architect designs within the budget and supervises execution; the quantity surveyor or construction cost consultant costs and checks; the project manager organises. The budget often slips between these roles, when each assumes the other is watching.

The client decides, and nothing relieves it of deciding. It sets the brief and the budget, approves changes, and signs contracts and change orders. It can delegate organisation, not decision-making. Homegrade uses the expression maître d'ouvrage délégué (delegated client) for the person to whom the client entrusts the handling of its interests on site; it is a contractual assignment, to be written up as such.

The architect designs within the budget and answers for those obligations. The architect's involvement is compulsory (1939 Law, art. 4), independence is ensured by the incompatibility with contracting (art. 6), and the budget is framed by art. 16 of the 2022 code. There is no longer a fee scale: the 2022 code contains none, and fees are negotiated in the agreement.

The quantity surveyor or construction cost consultant costs. Le Forem groups under the heading "métreur" the job titles of économiste de la construction, métreur-vérificateur and métreur-deviseur, and states that there is no statutory requirement to practise this occupation. Its value lies in independence from the contractor and in method: quantities, prices, the gap between estimate and actual cost.

The project manager organises. The role has no statutory status of its own; the assignment is the one its contract defines, which means it must be written precisely: what the project manager monitors, validates and reports, and to whom.

These intellectual service providers must be insured. The Act of 9 May 2019, in force since 1 July 2019, requires professional civil liability insurance for architects, surveyors, health and safety coordinators and other construction service providers who supply mainly intangible services, for a third party and on an independent basis. The client can ask for the certificate before signing.

The allocation rule fits into one sentence: one role, one contract, one person responsible. These points are developed in the branch on who manages cost for the client.

As at 21 October 2026, private construction contracts are governed by the old Civil Code. Articles 1787 and following, including articles 1793 and 1794 cited above, still apply. Book 7 of the Civil Code, "Les contrats spéciaux" (special contracts), was inserted by an Act of 22 July 2026, published in the Moniteur belge (Belgian Official Gazette) on 23 September 2026; Justel gives its entry into force as 1 September 2027. It is therefore not yet applicable.

The transitional rule draws the line by the date of the contract. Article 49 of the Law provides that Book 7 applies to legal acts and facts occurring after its entry into force; unless the parties agree otherwise, the previous rules continue to apply to the future effects of earlier acts. A works contract signed before 1 September 2027 will, in principle, remain governed by the old Civil Code until it ends, even if the works continue beyond that date.

For contracts concluded from 1 September 2027, several rules will change. Article 7.4.8 ("Sujétions imprévues", unforeseen difficulties) keeps the lump-sum principle: the service provider "may not claim any increase, even if the service required more work or expense than had been foreseen". It does, however, open the way to renegotiation if five cumulative conditions are met: pre-existing circumstances making performance excessively onerous, which could not have been known, are not attributable to the service provider, whose risk was not assumed, and whose consideration was not excluded; failing agreement, the court may adapt the contract or end it, without prejudice to article 5.74 on hardship. Article 7.4.32 will allow the client to terminate at any time, compensating expenses, losses, services performed and, unless custom provides otherwise, loss of profit. A section specific to immovable works (art. 7.4.55 to 7.4.57) deals with provisional and final acceptance and with a 10-year liability for defects that threaten stability or soundness, any clause that excludes or limits it being void.

One observation calls for caution. In its section on immovable works, Book 7 does not carry over the written authorisation rule of article 1793. That does not mean no written record will be needed any more: evidence and the contract remain. It means that, for contracts concluded from 1 September 2027, the written procedure for changes will have to be set out in the contract rather than expected from the law.

Hardship already applies today to some contracts. Article 5.74 of the Civil Code has been in force since 1 January 2023 for contracts concluded after that date; it is a default rule, so the contract can adjust or exclude it. This is a drafting point to deal with at signature. The article on what changes in 2027 with Book 7 of the Civil Code compares the two regimes article by article.

Six rules apply to any project in Belgium. They follow the order of the five moments.

1. Write the budget before the drawings, dated, complete and with an explicit contingency, in the architect's agreement concluded at the latest when the appointment is defined.
2. Name the region in the budget, since permits, energy requirements and charges depend on it, and apply no regional value outside its region.
3. Check the estimate at each stage, on the same basis of quantities, the same value date and the same items, and classify each variance as prices, quantities or brief.
4. Correct before tendering, starting with the brief and floor areas, since that is when correction costs least.
5. Allow no extra to be carried out without a written instruction and an agreed price, and cost every change to the brief through an additional agreement.
6. Keep the forecast final cost up to date at each interim valuation, and check, for each contract, whether it falls under the old Civil Code or Book 7.