The proyecto básico (basic design) defines the building and is enough to apply for the building permit; the proyecto de ejecución (construction design) develops it with the level of detail needed to build it. These are the two stages into which the Código Técnico de la Edificación (CTE, the Spanish Technical Building Code) allows a building project to be divided, which is why the basic design and the construction design appear as separate items in an architect’s fee proposal.
Law 38/1999 on Building Regulation (Ley de Ordenación de la Edificación, LOE) defines the project in Article 4 as the set of documents that establish the technical requirements of the works. Article 6 of Part I of the CTE adds that, for the purposes of administrative processing, it may be developed in two stages, and Annex I details what each one contains.
What the basic design is
Under Article 6.1.3 of the CTE, the basic design defines the general characteristics of the works and their performance through the adoption and justification of specific solutions. It fixes the siting on the plot, the massing, the layout and the floor areas.
The same article sets out its scope: its content is sufficient to apply for the municipal building permit or other administrative authorisations, but insufficient to start construction. With it, the local council checks that the building complies with the planning regulations.
For the client, this is the stage in which the design decisions are taken. What is approved here conditions the permit and all subsequent development, so it is worth arriving with the preliminary studies for the project already resolved.
What the construction design is
The construction design develops the basic design and defines the works in their entirety. It details the foundations and structure, the construction systems, the building services, the materials and the finishes, with their calculations, details and quantities.
The CTE imposes two limits on it: it may not lower the performance declared in the basic design, nor alter the uses and conditions under which the permit was granted, except in aspects that can be legalised. It also incorporates the partial projects that complete it, such as the services designs, as separate documents under the coordination of the lead designer.
It is the document the building is constructed from, under the supervision of the dirección facultativa (site supervision team), and the one that makes it possible to obtain comparable tenders from several contractors, because they all price the same items.
Differences between the basic design and the construction design
The building is the same in both documents. What changes is the level of definition and the use of each one.
| Aspect | Basic design | Construction design |
|---|---|---|
| Purpose | Define the building and demonstrate that it complies with planning regulations | Define the complete works so that they can be built |
| Level of detail | General characteristics, floor areas and solutions adopted | Structure, services, construction details and bills of quantities |
| Can be used to apply for the permit | Yes | Yes, when submitted together with the basic design |
| Can be used to build | No | Yes |
| Can be used to compare contractors’ tenders | No, it only allows estimates | Yes, with itemised quantities |
| Professional body stamp (visado colegial) | Voluntary | Compulsory for works that require a project under the LOE |
What documents each one contains
Annex I of Part I of the CTE lists the content of a building project (report, drawings, specifications, quantities and budget) and marks with an asterisk the sections that the basic design must include as a minimum.
| Document | Basic design | Construction design |
|---|---|---|
| Descriptive report | Complete: parties involved, background information, description and performance of the building | Complete |
| Construction report | Only the building’s support system | Structure, envelope, compartmentation, finishes and services |
| CTE compliance | At least, fire safety | All basic requirements, with their calculation annexes |
| Drawings | Location, site plan, external works, general floor plans, roofs, elevations and sections | In addition, structure, services and construction definition |
| Specifications | Not required | Yes |
| Quantities and budget | Approximate budget by chapters | Itemised quantities and detailed budget |
| Health and safety study | Not required | Yes, or a basic study depending on the scale of the works |
Royal Decree 1627/1997 requires the health and safety study to form part of the construction design. Royal Decree 105/2008 requires it to include a construction and demolition waste management study, part of whose content must already appear in the basic design submitted for the permit.
Why the works cannot start with the basic design alone
The CTE itself declares the basic design insufficient to start construction. It does not define the structure, the services or the construction details, nor does it include the health and safety study that the works require.
When the permit is granted on the basis of a basic design, the construction design still has to be submitted before work begins. In the Region of Madrid, Article 154 of Law 9/2001 on Land establishes that, to start the works, a responsible declaration is sufficient, stating that the construction design develops the basic design and does not introduce substantial changes.
The form and timing of that submission depend on regional legislation and on each municipality’s by-laws. The remaining procedures are explained in the guide to permits for building a house.
Difference between the anteproyecto and the basic design
The anteproyecto (concept design) is an earlier stage of work that the CTE does not regulate. It sets out the architect’s initial proposal in floor plans, elevations, massing and a first cost estimate, so that the client can validate the idea before developing it.
It has no administrative standing: a building permit cannot be applied for with a concept design. The basic design starts from that already accepted design, adjusts it to planning and technical regulations and gives it the minimum documentary content of Annex I.
Professional body stamp: when it is compulsory
Royal Decree 1000/2010 on the compulsory visado colegial (stamp of approval by the professional body) limits the obligation to a closed list of work. In building, Article 2 includes the construction design and the final works certificate, provided they relate to works that require a project under the LOE.
The basic design is not on that list. Its stamp is voluntary and is only processed at the client’s express request.
The stamp must be obtained before the work is submitted to the Administration. The professional body checks the identity and professional qualification of the author and the formal correctness of the documentation; it does not look at fees or carry out technical control of the content.
When to commission the basic design and the construction design together
Both stages can be drawn up and submitted in a single document, known as the proyecto básico y de ejecución (combined basic and construction design). The permit is then applied for with the complete project and, once granted, there is no second stage left to submit.
This approach is advisable when:
- The brief and the design are settled and no changes are expected.
- The planning regulations for the plot are clear and there are no sectoral or heritage-protection reports pending.
- The work is a refurbishment or a project of little complexity.
- You want to request tenders from contractors while the permit is being processed.
Separating the stages is more prudent when there is planning uncertainty. If the council requires changes, only the basic design has to be redone, not the whole technical development. The effect of each option on the timeline is analysed in the article on how long a new-build project takes.
What happens if the project is changed after the permit
It depends on the scope of the change. Adjustments that do not alter the conditions of the permit, such as a finish or a construction solution, are recorded in the construction design or in the final works documentation.
Changes that affect what the council authorised (volume, built area, site coverage, height, use or number of dwellings) require a modification of the permit to be processed before they are carried out. What counts as a substantial modification, and how it is processed, is set by each municipality’s regulations.
During the works, the LOE assigns the director de obra (works director) the task of drawing up modifications to the project, at the client’s request or with their consent. On completion, the project is handed over to the client with the approved modifications already incorporated.
How Cabana works through the project stages
Cabana is an architecture studio in Madrid that prepares basic and construction designs for detached houses, full refurbishments and corporate architecture. On each commission, we assess with the client whether it is better to apply for the permit with the basic design or with the complete project, and the studio coordinates the partial projects that make up the construction design. Our services are detailed on the page of the architecture studio in Madrid.
In summary
The basic design and the construction design are two stages of the same project. The first defines the building, demonstrates that it complies with planning regulations and makes it possible to apply for the permit. The second develops it to the level of detail needed to build and to contract the works with itemised quantities.
The works cannot start without the construction design. Commissioning both in a single document saves a procedure when the design is settled; separating them reduces the risk when the permit may force changes.
Frequently Asked Questions
Who can sign the basic design and the construction design?
The LOE assigns the drafting of the project to the designer, who must hold the qualification required for the use of the building. When the main use is residential, that qualification is that of architect.
Can the basic design budget be used to contract the works?
No. The CTE only requires it to contain an approximate valuation of the material execution by chapters, without itemised quantities. A contractor cannot commit to a fixed price with that information.
Does a refurbishment need a basic design and a construction design?
Only if the intervention requires a project under Article 2 of the LOE: total interventions or interventions on protected elements, or partial interventions that substantially alter the external composition, the massing or the structure as a whole, or that change the characteristic use of the building.
Can a council demand the construction design before granting the permit?
The CTE considers the basic design sufficient to apply for it, but the specific documentation depends on the procedure and on the municipal by-laws. It is advisable to check the council’s requirements before deciding how to split the commission.
What documentation does the client receive when the works are finished?
The works director provides the project with the modifications approved during construction. Together with the handover certificate, the list of parties involved and the use and maintenance instructions, it forms the Libro del Edificio (Building Logbook).
