Extras in a private lump-sum contract

The text covers a specific case: the construction of a building for a lump sum, on the basis of a plan settled and agreed with the owner of the land. In that case, the architect or the contractor cannot obtain any increase in price, either because labour or materials have become more expensive or because of changes or additions to the plan, "if those changes or additions have not been authorised in writing and the price agreed with the owner" (unofficial translation). The text sits in Book III, title VIII, chapter III, section III "On estimates and contracts" (Des devis et des marchés) of the Civil Code.

Two cumulative conditions must be met for a change to give rise to an extra: written authorisation of the change and agreement on its price with the owner. One without the other is not enough on the wording of the text. A written instruction without a price leaves the amount open to argument; a price accepted without written authorisation leaves open the question of who asked for the change. The safest course is to record both on the same document.

If one of the starting conditions is missing (no genuine lump sum, no settled plan), the protection of the article does not apply on its terms, and the question of the extra is settled under the contract and the general rules of evidence.

Condition	What it assumes	What the client should watch
Lump-sum contract	a global price for the work, not unit rates applied to quantities	in a mixed contract, only the lump-sum part has a global price
Construction of a building	the subject of the contract is a building	check that the contract covers the whole work or an identified part of it
Settled and agreed plan	drawings fixed and accepted by both parties at signature	incomplete drawings at signature weaken the lump sum
Written authorisation	a written decision by the owner	an oral agreement at a site meeting does not replace it
Agreed price	an amount accepted by the owner	fix it before execution: a price "to be seen in the final account" is not an agreed price

There is only one state of the law to present. On the date of checking, no text reforming these articles of the Civil Code had been identified: the rules described here are those that apply to contracts signed today.

The lump sum covers increases in the contractor's costs. The text expressly rules out an increase in labour or materials as grounds for an extra. If the contract contains a price revision clause, that clause applies, and it is tracked on a separate line of the dashboard (see the article in this branch on price revision and the budget's base date).

The lump sum covers what the settled drawings describe, and only that. The more precise the contract documents at signature, the sharper the scope of the lump sum. Drawings that defer choices until later (finishes, equipment, options) create as many future extras, which article 1793 does not prevent if they are requested and accepted in the proper form. Nor does the lump sum shift the risk of a defective description onto the contractor: the distinction between measured and lump-sum contracts, and what it implies for quantities, is covered in the article on measured and lump-sum contracts.

The lump sum does not cover changes the client wants. Each change of brief during the works gives rise to a legitimate extra, provided it is authorised in writing and its price agreed. The discipline of the text is not meant to prevent changes but to make them visible and priced before they are carried out. How to describe and price this work is set out in the article on additional works.

The best way to apply article 1793 is a written procedure provided for in the contract before the first day on site. The clauses to negotiate at signature are presented in the article on the private contract: inviting, negotiating, signing a lump sum. Their effect on the budget comes down to four steps:

1. The request. Every change, whether it comes from the client, the architect or the contractor, is recorded on a numbered change form describing the change, the drawings and the items affected.
2. The costing. The contractor submits a price excluding VAT (HTVA), as an addition or an omission, with any effect on the programme. Omissions are tracked as rigorously as additions: an item removed and not deducted is a hidden extra.
3. The decision. The client authorises the change and accepts the price in writing, on the same document. The client signs: the architect advises and checks, but the spending decision is the client's, unless there is a written and limited mandate.
4. Recording, then execution. The signed form goes onto the approved extras line of the dashboard described in the article on tracking the final cost during the works; a form that has been priced but not signed stays on the extras under discussion line. No changed work starts before signature. In a genuine emergency, immediate written authorisation, even by email, followed by the price within a period set in the contract, is better than an oral agreement.

Document	Minimum content	Signed by
Change form	number, description, drawings and items affected, origin of the request	author of the request
Price quotation	amount excluding VAT, addition or omission, effect on the programme	contractor
Authorisation	agreement on the change and on the price, date	client
Change register	running total of approved extras and extras under discussion	client or its adviser

The text works in the client's favour, but in practice the argument is about proof. Who asked for the change, who accepted it, at what price: everything turns on those facts. Ambiguous emails, site meeting minutes recording a change without reservation, interim payments made without dispute can all be raised against the client. For work in several parts or measured work, the Civil Code also provides that inspection is deemed done for the parts paid when the owner pays in proportion to the work done (art. 1791).

Three reflexes limit this risk. Dispute in writing, without delay, any invoice containing an unauthorised item. Have the minutes record that a change mentioned at a meeting remains subject to written authorisation and a written price. Never pay an extra "to keep things moving" without a document fixing its amount.

On the dashboard, a disputed extra stays in at its likely amount. Removing it because article 1793 seems to favour the client amounts to betting on the outcome of a dispute.

The same change often has two effects: on the contractor's price, and on the brief of the architect or consulting engineer (ingénieur-conseil). The Grand-Ducal regulation of 17 June 1992 setting the code of conduct for architects and consulting engineers provides, in its article 9, that "any significant change to the brief set in the agreement, occurring during the design or execution of the works, must be the subject of an additional agreement stating its financial impact" (unofficial translation).

For the client, this is a second safety net. A change of brief requested during the works thus leaves two traces: the authorisation and the price on the contractor's side, the additional agreement (convention additionnelle) on the designer's side. When both are missing, the budget drifts without anyone having priced it. Article 13 of the same regulation states that the architect assists the client (maître de l'ouvrage) in choosing the parties involved "with a view to carrying out the project on the best terms of price and quality": asking the architect to check every price quotation for an extra fits that logic.

The client can end the lump-sum contract unilaterally. Article 1794 of the Civil Code provides: "The owner may terminate the lump-sum contract unilaterally, even though the work has already begun, by compensating the contractor for all its expenses, all its work, and everything it could have earned from the undertaking."

It is an exit, not a saving. The cost of termination includes what has been carried out, the expenses incurred (orders, supplies) and the lost profit on the part not carried out, to which must be added the price of the contractor who will finish the work. Before using this lever to escape a drifting budget, it has to be priced as one option among others, alongside reducing the brief, and provided for. A compensation clause in the contract should be read in that light.

In public contracts, the logic is different: the law of 8 April 2018 governs changes through defined cases and ceilings, and the implementing regulation requires the form of an amendment. See the article on amendments to a public contract in progress.

After acceptance, the question is no longer price but liability. Ten-year liability under article 1792 and discharge under article 2270 are covered in the article on liability after handover.