What the LOE allocates, and what it does not
The LOE organises the building process around agentes (parties) with defined duties. The parties are all the persons "who take part in the building process" (art. 8; unofficial translation). The promotor is the one who "decides, drives, programmes and funds" the works (art. 9.1); the designer drafts the design "on the commission of the promotor" (art. 10.1); the contractor is bound "contractually to the promotor" (art. 11). The full allocation of roles is covered in the article on the building agents under the LOE, and what the law requires of the promotor itself in the one on the developer's obligations.
The LOE does not use the word "presupuesto" (budget) in the sense of cost. Cost only comes up as the final cost of the net works (the handover record, art. 6.2.c, and the guarantees, art. 19) and through the certificaciones (interim certificates) and the liquidación (final account). The decision on the budget belongs to the promotor; the law names nobody to defend it on the client's behalf.
The site direction records cost, it does not control it
The director de la ejecución de la obra (works execution director) prepares and signs "the interim certificates and the final account of the work units carried out" (art. 13.2.e), and the director de obra (works director) approves them (art. 12.3.e). This is a function of measuring what has been built: it says how much has been done and at what price, not how much the works will cost in the end.
The director de obra also prepares changes to the design "at the request of the promotor or with its agreement" (art. 12.3.d). The law puts the decision in the hands of the promotor, but does not require anyone to price each change before it is approved: if the site direction contract does not demand it, the client can agree to a change without knowing its cost. The same applies to public works: certificates are payments on account, "without in any way implying approval and acceptance of the works" (art. 240.1 of the Public Sector Contracts Act, LCSP), not a validation of the final cost.
Three roles to entrust with cost control
Control of the forecast cost is an assignment that is contracted, with three possible roles that are not mutually exclusive.
| Role | On whose behalf | What it controls | Where the obligation comes from |
|---|---|---|---|
| Architect or arquitecto técnico (building engineer) with a cost assignment | Promotor | Budget at each stage, pricing of changes, forecast of final cost | Professional appointment, beyond the site direction |
| Project manager or dirección integrada de proyecto (integrated project direction) | Promotor | Scope, cost, time and quality, at every stage | Project management contract |
| Project monitoring | Lender granting the development loan | Consistency between works carried out, cost and drawdowns of the loan | Bank requirement, contract with the monitor |
The decisive difference is who gives the mandate. Project monitoring protects the loan, not the promotor's budget, even though the two interests often coincide. The other two roles work for the promotor, with whatever effect their contract gives them.
Neither the fees nor the scope of these assignments are regulated. The professional body's validation (visado colegial) "shall in no case cover the fees or the other contractual terms" (art. 13 of Ley 2/1974), and the professional bodies may not set guideline fee scales (art. 14). Everything is agreed between the parties.
What is worth putting in writing
A cost control assignment is useful if it fixes three things: what is delivered, when and with what authority. The deliverables: an estimate at each stage with the same structure and price date, the pricing of each change before it is approved and a forecast of final cost updated with each certificate.
Decision-making authority is the clause most often forgotten. Whoever watches cost should not be able to approve changes or extra works without the promotor's written delegation. Under a fixed-price contract, article 1593 of the Civil Code allows a price increase for changes the owner has authorised, and, according to legal commentary, several Supreme Court judgments have accepted tacit authorisation: an adviser who appears to have authority can commit the budget without meaning to.
The articles in this branch
- The article on project manager, integrated project direction and project monitoring compares the three roles, who gives each its mandate, their deliverables and what their contract should contain.
- The article on what the LOE says, and does not say, about construction cost goes through the three places where cost appears in the law and what follows from them for the promotor.
This article reflects the state of the rules on the date of verification, 21 October 2026, and is intended as professional guidance. It does not replace legal advice or an examination of the specific case.