The written order and the tender price
Every modification starts with a written order. Article 80 of the RGE provides that modifications to the contract are ordered in writing. An oral order may be treated as equivalent to a written order where the contractor notifies it within 48 hours, by registered post or an equivalent electronic means, to the fonctionnaire dirigeant (supervising official), under the conditions the article sets out.
Valuation starts from the unit prices in the tender. This is the contracting authority's first budget protection: changed work that corresponds to an existing item in the métré (meetstaat, bill of quantities) is paid at the price already put out to competition. The discussion therefore concentrates on new items, with no equivalent in the tender, and that is where price checking must focus.
Practical consequence. The more complete and detailed the initial bill of quantities, the larger the share of modifications valued at tender prices. The article on measurement in Belgian public contracts deals with that preparation.
The permitted cases of modification
The RGE does not allow a contract to be modified freely. It lists cases, each with its conditions, and forbids anything that would turn the contract into a different contract.
| RGE article | Case | Ceiling | Budget reading |
|---|---|---|---|
| 38/1 | additional works | 50% of the initial amount, per modification | a heavy modification, to be funded outside the ordinary contingency |
| 38/2 | circumstances a diligent contracting authority could not foresee | 50% of the initial amount, per modification | the genuine unforeseen event, which the contingency must absorb |
| 38/3 | replacement of the contractor | specific conditions | effect on price to be analysed case by case |
| 38/4 | low-value modification | below the European threshold and below 15% of the initial amount for works, in cumulative net value | the accumulation of small modifications |
| 38/5 and 38/6 | non-substantial modification; definition of a substantial modification | a substantial modification is forbidden | beyond that, a new contract is needed |
The European threshold for works is set at 5,404,000 euros HTVA (excluding VAT) by article 11 of the Royal Decree of 18 April 2017 on the award of public contracts. As long as the initial amount of the contract remains below about 36 million euros excluding VAT, 15% of that amount stays below the European threshold: in the case of article 38/4, it is then the 15% ceiling that applies first.
"Per modification" does not mean "in total" (unofficial translation, as are all quotations of legal texts below). The 50% ceilings in articles 38/1 and 38/2 are assessed modification by modification. Legally, two separate modifications may each remain below the ceiling; in budget terms, they add up on the same envelope.
"In cumulative net value" means that small modifications are counted together. A series of low-value modifications, each harmless on its own, ends up reaching the 15% ceiling; the change register is what lets you see it coming.
What no modification allows
A substantial modification is forbidden. Articles 38/5 and 38/6 of the RGE distinguish the non-substantial modification, which is permitted, from the substantial modification, which article 38/6 defines and which requires a new award procedure.
For the budget, the consequence is clear. If the brief changes to the point where the modification would become substantial, the contracting authority cannot absorb it within the current contract. It must launch a new procedure, with its cost, its timescale and the risk of higher prices. It is better to identify this at estimate stage than during the works.
The review clause
The RGE also provides for the case where the balance of the contract is upset. Article 38/9 organises a review clause where the contractual balance is upset to the contractor's detriment. For works, the loss must reach at least 2.5% of the initial contract amount (§ 3). Article 38/10 covers the opposite case, where the upset works to the contractor's benefit.
For the contracting authority, a request based on article 38/9 is a line in the dashboard. It is entered among the modifications under discussion, at its probable amount, as soon as it is announced. Its examination follows the conditions of the article, which cannot be reduced to the 2.5% threshold.
Entering each modification in the budget
The management rule fits in one sentence: every modification has a number, a legal basis, an amount and a source of funding. The contracting authority's change register contains at least the following columns.
| Column | What it allows you to check |
|---|---|
| Number and date of the written order | the form required by article 80 |
| RGE article relied on | the case of modification and its conditions |
| Amount excluding VAT, upwards or downwards | the effect on the final cost |
| Share valued at tender prices, share at new prices | where price checking must focus |
| Running total of low-value modifications | the distance to the 15% ceiling in article 38/4 |
| Ratio to the initial amount, per modification | the distance to the 50% ceiling in articles 38/1 and 38/2 |
| Remaining contingency | the budget's capacity to absorb what follows |
Fictitious example. A works contract awarded for an initial amount of 1,000,000 euros excluding VAT. Three small modifications of 40,000, 55,000 and 35,000 euros, treated as low-value modifications, total 130,000 euros: that is 13% of the initial amount, close to the 15% ceiling of article 38/4. If the budget's contingency had been set at 80,000 euros, it is already exceeded, even though no rule of the RGE has been broken. That is the difference between a legal ceiling and a budget envelope. The forecast final cost is therefore updated at each modification, using the method described in the article on tracking the final cost during the works.
Modification or quantity variance
A quantity carried out that exceeds the provisional quantity is not necessarily a modification. If the contracting authority has changed nothing in the contract and the actual quantity simply departs from the provisional quantity, it is article 81 of the RGE that applies, independently of any modification. The two mechanisms add up in the forecast but are not confused in the register. The article on what quantity variances do to the final cost deals with that second case.
What a private contract does differently
In a private marché à forfait (lump-sum contract), there are neither listed cases nor ceilings. The protection of the maître d'ouvrage (bouwheer, the client) rests on article 1793 of the old Civil Code: no extra without a change authorised in writing and an agreed price. The article on extras in a private lump-sum contract derives the procedure from it. What the two regimes have in common is writing before execution.
This article reflects the position of the rules at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.