What the note is for
It turns a gap into a choice. An overall figure ("the estimate is over by so much") does not allow a decision. Broken down into causes and set against priced options, it becomes a list of possible decisions, each with its saving, its risk and its effect on the timetable.
It sets the reference for what follows. Once signed, the note becomes the basis of the convention additionnelle (additional agreement) that the architect must draw up for any change to the programme, stating its financial impact (code of ethics of the Order of Architects of 16 November 2022, art. 16). It also serves as evidence if the gap were to be disputed later.
It is drawn up before tendering. That is when all the levers remain open, as explained in the article on the estimate that exceeds the budget before tendering.
The five-block structure
- The quantified gap, with its price date. Reference budget, current estimate, gap in amount and as a percentage, all excluding VAT (HTVA) and expressed at the same price month. One line states the phase of the estimate (preliminary design, permit application, construction documents) and the items included.
- The causes, broken down. The gap is split between three causes: prices (unit prices, price date effect), quantities (areas and measured quantities with the programme unchanged), programme (additions or changes since the budget was set). The three must add up to the gap: any unexplained remainder is to be flagged as such.
- Three to five options. Each option is described in one line, with the estimated saving, the risk (quality, use, technical, permit) and the effect on the timetable. The options follow the order of effectiveness: programme and areas, level of finish, options and conditional items, phasing, procurement route. Drafting options and conditional items is a matter for the specification: see the article on variants, options and conditional items.
- The decision. The options adopted, the total saving, the new reference budget, and anything left uncovered, accepted as an increase in the budget. A partial decision is still a decision: it is written down.
- The written record. Date, signatories, attachments (estimate, drawings concerned), and follow-up actions: an additional agreement for changes of programme, an updated estimate, incorporation of the options into the specification.
Entirely fictitious example
The example below is entirely fictitious: the project, the amounts and the choices are invented to illustrate the method. They are neither a reference price nor a market indication.
A client is having an office building built. Reference budget: 800,000 euros excluding VAT, set at a price date written into the architect's agreement. The preliminary design estimate, brought to the same price date, reaches 920,000 euros excluding VAT, a gap of 120,000 euros.
Causes broken down: 50,000 euros come from the programme (a meeting room added during sketch design, without an additional agreement), 40,000 euros from quantities (a more extensive facade than planned), 30,000 euros from prices (price references more recent than those of the budget). Together they equal the gap of 120,000 euros, with no remainder to explain.
| Option | Estimated saving (excl. VAT) | Risk | Effect on the timetable |
|---|---|---|---|
| A. Remove the added room, meetings held in the shared space | €45,000 | Less comfortable use | None, drawings to be revised |
| B. Simplify the facade (fewer setbacks) | €30,000 | Architectural appearance altered | Slight, to be checked against the permit |
| C. Make the landscaping of the surroundings a conditional item | €25,000 | Surroundings completed later or not at all | None |
| D. Change the range of floor finishes | €20,000 | Durability and maintenance | None |
| E. Defer the carport to a second phase | €15,000 | Higher total cost in the long run | Second intervention to plan |
Decision (fictitious): the client adopts A, B and C, a saving of 100,000 euros. The client rejects D (durability judged a priority) and E (long-term cost). The remaining 20,000 euros are accepted as an increase in the reference budget, raised to 820,000 euros excluding VAT. The architect draws up an additional agreement for the removal of the room and the change to the facade, and includes the surroundings as a conditional item. In this fictitious case, the note shows that the largest share of the gap came from a decision by the client, which steers the discussion towards the programme rather than prices.
The mistakes that make the note useless
- Comparing at different dates. If the budget and the estimate are not expressed at the same month, part of the gap is artificial, and the options are poorly calibrated.
- Presenting a single option. A note that offers only one solution arbitrates nothing: it asks for approval. At least three options allow a real choice.
- Adding up savings that overlap. Simplifying a facade and changing its material do not always add up. Each saving must be estimated taking account of the options adopted alongside it.
- Funding the gap from the contingency. That reserve covers site risks, not the estimating gap. Homegrade, in the Brussels-Capital Region, recommends a reserve "of the order of 10% of the value of the works" (brochure "Maîtriser son chantier", 2022, unofficial translation): an option that removes it is not a saving.
- Forgetting the follow-up. A decision that triggers neither an additional agreement nor an updated estimate remains a dead letter at tender stage.
- Letting the architect decide. The architect proposes and prices, and assists the client; the decision belongs to the client. The checking method that precedes the note is described in the article on checking the architect's estimate.
This article presents a method as at 21 October 2026 and is intended for professional orientation. It replaces neither legal advice nor an examination of the specific case.