A different figure at each stage
The first trap is to read as a price what is only a valuation. The Código Técnico de la Edificación (the Technical Building Code, Royal Decree 314/2006, art. 6) provides that the proyecto básico "shall define the general characteristics of the works" (unofficial translation) and is enough to apply for the building licence, but not to build; the proyecto de ejecución develops it. The cost figure follows the same path: approximate at the start, detailed at the end. For the proyecto básico, Annex I of the CTE, as worded by Royal Decree 173/2010, requires at least an approximate budget, that is, an "approximate valuation of the material execution of the designed works, by trade section".
| Stage | Cost figure | What it is for | What it is not for |
|---|---|---|---|
| Preliminary studies and outline design (estudios previos, anteproyecto) | whatever the appointment asks for | validating the order of magnitude of the brief | committing the budget |
| Proyecto básico | approximate budget of the net works cost | applying for the licence, first comparison with the budget | contracting the works |
| Proyecto de ejecución | itemised quantities and a detailed budget by trade section | obtaining comparable bids, setting the contract budget | knowing the total development cost |
| Public works | budget with unit prices, price breakdowns and schedule of quantities (LCSP art. 233.1.d) | underpinning the base tender budget | replacing the review of the design |
The content of each document is described in the articles on the basic design and on the detailed design in the guide to project phases. Here, only the effect on the budget matters. None of these figures is the total cost: fees, licences, insurance, utility connections, financing and VAT (IVA) are added by the client in its own budget.
Three checks before accepting an estimate
Comparing two figures that do not measure the same thing produces false reassurance or a false alarm. Before discussing the amount, the client checks three things.
The scope. What does the design estimate include? Internal site works, demolition, fixed furniture, special installations, provisional sums still to be defined. Every exclusion should be written down.
The price date. An estimate prepared with prices from a year ago cannot be compared with a client budget set this month. Ask for the date of the prices and the database they come from.
The structure. The trade sections of the design estimate must be readable against the items in the client's budget: if one works by trade sections and the other by major building systems, the difference cannot be located. It is worth setting a common structure in the appointment and keeping it from one stage to the next.
Once the three checks are done, the difference that remains is real and has a cause: brief, specifications, quantities or prices. The brief and the specifications come down to a decision of the client; quantities and prices are discussed with the designer.
The independent counter-estimate
When the figure is decisive, it is tested against an estimate made by someone else. This is not about redoing the design, but about pricing the same documents with one's own measurements and prices, to see where they diverge. The method is simple: same scope, same price date, same structure of trade sections, and a list of the assumptions made where the design does not define them.
What weighs most is usually the measurement, not the price. A quantity forgotten or counted twice in a major trade section moves the result more than a difference in unit price. The usual mistakes are reviewed in the article on quantity take-off errors. The best time to commission the independent counter-estimate is before each stage is closed, above all at the end of the proyecto básico and before going out to tender.
Who decides
The decision on the budget belongs to the promotor (the client). Law 38/1999 on Building Regulation (Ley de Ordenación de la Edificación, LOE) defines the promotor as the person who "decides, drives, plans and finances" the works (art. 9.1), and the designer works "on the instructions of the promotor" (art. 10.1). No text makes the architect the keeper of the client's budget: what is required of the architect on cost depends on the appointment. That is why every deliverable should come with its cost figure compared in writing with the budget, and every deviation with a signed decision.
The articles in this branch
- The article on the approximate budget of the proyecto básico explains what that first valuation of the net works cost covers, what it does not cover and what else to ask for so that it can serve as a control.
- The article on what to do when the design estimate exceeds the client's budget sets out how to diagnose the overrun and the levers available before contracting; its follow-on article offers a model decision note.
- The article on the architect's liability for cost overruns summarises the trend in published decisions and explains why the client's protection comes from the contract.
- The article on the design budget in public works covers the market prices required by the LCSP, the mandatory design review and the cost of a badly calculated base budget.
This article describes the state of the rules on the date of verification and is intended as professional guidance. It does not replace legal advice or an examination of the specific case.