The design phases in Spain: from preliminary study to detailed design

The sequence is not cumulative bureaucracy: it is progressive risk management. Each stage invests just enough to decide whether the next one deserves its cost, and freezes what has been decided so later work does not reopen it. Skipping stages saves apparent fees and returns them multiplied in modifications.

The first two stages concentrate the project's economic power. In the preliminary studies, the site's planning feasibility is checked, the brief is set and the cost envelope is estimated by ratios; in the anteproyecto, the architectural solution takes shape and with it the variables that weigh most in the final budget: real built area, compactness, cores, structural system. Neither document processes anything, and precisely for that reason they are the natural territory of iteration: changing here is free, changing later no longer is. The detail of both stages is developed in the article on preliminary studies and the anteproyecto.

The proyecto básico defines the building completely in its essentials and enables the works licence application, but is not enough to build. Its regulatory content, set by the corresponding annex of part I of the CTE (Código Técnico de la Edificación, the Spanish building code), includes the descriptive and planning report, the general drawings and the estimated budget; it leaves out the construction detail, the developed services and the complete quantities. In schedule management, the básico is the piece that allows parallelisation: licence in process while the detailed design is developed. Its exact scope and limits are analysed in the article on the proyecto básico.

The proyecto de ejecución develops the básico until the works are executable and contractable: detail drawings, construction report, complete regulatory justification, specifications, and the economic block with the mediciones (bill of quantities) and the budget. It is the only document of the sequence subject to obligatory professional validation, and the one that serves as the basis for the works contract, the monthly certifications and the final settlement: each of its documentary gaps reappears later as an economic conflict. Its content and the central role of the quantities are developed in the article on the proyecto de ejecución.

The first is designing without an economic envelope: reaching the básico without a checked target budget turns the detailed design into a lottery and the works tender into a disappointment. The target budget is set before the básico and checked at each stage.

The second is treating the básico as a minor formality: the básico's imprecisions are paid in municipal requirements, and the differences between the licensed básico and the developed detailed design, in licence modifications. The básico conditions the licence and with it the whole calendar.

The third is closing the detailed design with incomplete or inherited quantities: the classic source of certification conflicts and new rates on site. Quantities are redone on the actual design rather than inherited.

The fourth is forgetting coherence between stages: each document must be traceable to the previous one, because discrepancies between versions are ammunition in any later dispute. Traceability is checked before each document is delivered.