Choosing an architecture studio well means first understanding what you are buying. For major works, Spanish law requires a project, an architect and a technical architect. Fees are calculated as a percentage of the cost of the works and usually run from 5% to 15% depending on complexity. And between the commission and the first day on site, months pass, not weeks.

This guide covers each piece — the legal obligation, the stages, the money, the permits, the timescales and the guarantees — and ends with the questions to ask at a first meeting. Rules vary between municipalities, so always confirm the procedural and tax detail with your own ayuntamiento.

Am I legally required to hire an architect?

Yes, whenever the work is new construction or alters the architectural configuration of the building: its structure, its volume, its envelope or its use. In those cases Spain's Ley 38/1999 de Ordenación de la Edificación requires a project signed by an architect and a dirección facultativa on site, made up of the site director — the architect — and the director of execution — the technical architect, or aparejador. It is not optional, and it does not depend on how much you spend.

An interior renovation that touches no structure, façade or use is normally handled through a comunicación previa or a declaración responsable, and may need no project at all. The line is not drawn by budget. It is drawn by what you touch.

The execution project and the final works certificate also require the architects' association stamp, the visado, under Real Decreto 1000/2010. The visado verifies the identity and standing of the professional signing and the formal completeness of the document. If someone offers to skip it on a job that needs it, the issue is not the saving: the file does not stand up.

What stages does a project have, and what do I get at each one?

A building commission is delivered as documents, and each document does a different job. Confusing them causes most budget misunderstandings.

• Preliminary design (anteproyecto). The idea, the areas, the massing and a cost estimate. It is there to help you decide, not to apply for anything or to build.
• Basic project (proyecto básico). Defines the solution and demonstrates compliance with planning rules. It is the document the licence application is built on. It is not enough to build from.
• Execution project (proyecto de ejecución). Develops the basic project into construction detail, structure, building services, quantities and costs. This is what a builder needs to price properly and to build.
• Site management. Supervision during construction. The architect directs the design and answers for the result; the technical architect controls the physical execution, the materials and the safety plan.
• Final works certificate and the building manual (libro del edificio). These close the file and document what was actually built and how to maintain it. Without them there is no occupancy licence.

A proposal that does not say which of these it includes cannot be compared with another. Two very different figures may cover very different work.

What do the fees cost, and what else do I pay?

Architects' fees in Spain have been unregulated since 1997: there is no official tariff, and professional association scales are indicative only. In practice they are calculated as a percentage of the material execution budget of the works. For a new-build single-family home they usually sit between 5% and 12%; for a full renovation or refurbishment they often rise to 10–15%, because the design work per euro built is greater — the existing fabric has to be surveyed, the structure verified, and junctions resolved that a new build simply draws from scratch.

The architect's fee is not the only technical cost. Also budget for:

• the technical architect who takes on the direction of execution;
• any preliminary studies the project needs: geotechnical, topographic, or opening up an existing building to inspect it;
• building services engineering and the health and safety study, if not included;
• the visado;
• the ICIO construction tax and the municipal licence fee;
• the compulsory insurance for the works.

ICIO is a municipal tax on the real cost of construction, and each ayuntamiento sets its own rate, so it has to be checked in that municipality's tax ordinance. Many of them discount works for energy retrofit or accessibility, sometimes substantially. Ask before you file, because some reliefs have to be claimed at the point of application.

Which permits do I need, and how long do they take?

Works follow one of two routes. A major works licence applies to new build, extensions and any intervention affecting structure, envelope or use: it requires a project, a qualified professional and an express decision from the ayuntamiento. Minor works go through a declaración responsable or comunicación previa, which let you start sooner but exempt you neither from the rules nor from the fees.

On timing, each autonomous community's planning law sets a maximum period to decide, usually three months. That clock only starts once the file is complete, and it stops every time the ayuntamiento asks you to correct something. In practice, with complete paperwork, simple works are resolved in weeks and a new build or structural intervention runs to several months.

Do not plan around administrative silence. For planning licences silence is generally negative, and a licence that would contravene the planning rules can never be acquired by silence. If the ayuntamiento does not answer, what you have is not permission: it is a problem.

How long from the commission to the first day on site?

Longer than almost anyone expects. For a single-family house, six months to a year between the first meeting and breaking ground is normal, roughly split as:

• surveying the property and the preliminary design, with the client's decisions in between: weeks;
• basic project and licence application: weeks;
• municipal processing: one month to several, depending on complexity and on how many corrections are requested;
• execution project, which can run in parallel with processing;
• tendering to builders, comparing bids and signing a contract: several more weeks.

Two things stretch this calendar above all: client decisions that get postponed, and incomplete paperwork at submission. Neither of them is the ayuntamiento's doing.

What if the building is old?

In the Basque Country, residential buildings must pass the Inspección Técnica de Edificios when they reach 50 years old and repeat it every ten. So must listed or protected buildings, whatever their age, and it is a condition of applying for public refurbishment grants.

The ITE is more than a formality: the report covers the state of conservation, the energy certificate for the whole building and an accessibility assessment, and it incorporates the building manual or maintenance plan if the owners' association has none. On a refurbishment it is the best available starting picture, and it is worth having before commissioning the project rather than after.

What guarantees do I have if something goes wrong?

The Ley de Ordenación de la Edificación sets three periods of liability from handover: ten years for damage affecting the structure or the stability of the building, three years for damage to construction elements or services affecting habitability, and one year for finishing defects, which the builder answers for.

Residential buildings also require the compulsory ten-year insurance covering structural damage. Ask from the outset who holds each policy and what documents you receive at completion: the building manual and the final works certificate are the papers that let you claim years later if something fails.

So how do I choose a studio?

With all of the above on the table, the decision stops being a comparison of photographs. What separates one proposal from another is:

Experience with your problem, not your style. A single-family house, a listed refurbishment, a housing development and a tertiary building have little in common. Ask for references of the same type of commission, and ask what the studio actually did on each: drew the project, inherited it from another professional, handled the permits, ran the site.

Scope in writing, stage by stage. Which documents are delivered, which procedures are taken on, what falls outside, and how changes of scope are handled once work has started.

Who signs and who turns up on site. Rarely the same person who presents the proposal. The visiting frequency and your day-to-day contact shape the experience more than anything else.

Knowledge of the municipality. Getxo's planning rules are not Barakaldo's, and each ayuntamiento's view of what paperwork it wants is learned by filing there.

A fee proposal you can audit. Fees by stage, what costs are excluded, and what assumptions the figure rests on.

Questions for the first meeting

1. Have you done something like this, and which part did you take on?

   Look for the same type of property and the same stage, not the same style. Ask whether they drew the project from scratch, modified someone else's, handled the licence, and ran the site.

2. Which documents do you deliver, and which fall outside?

   Preliminary design, basic project, execution project, site management, final certificate. A proposal that separates them by stage, each with its fee, is one you can compare with another.

3. Who signs the project, and who will visit the site?

   And how often. Ask who takes on the direction of execution, and whether the studio proposes them or you contract that separately.

4. What has to be checked on this property before committing to a solution?

   A studio that knows the ground answers with a concrete list: applicable planning rules, heritage protection, state of the structure, access, services. A generic answer means they have not looked at your case yet.

5. Which technical costs are not in your fee?

   Technical architect, geotechnical or topographic studies, services engineering, visado, fees and ICIO. Knowing what is missing stops you comparing two numbers that cover different things.

6. How long until we can start on site?

   Ask for the breakdown by stage, including municipal processing. An honest answer says which part of the calendar is outside the studio's control.

7. What do you need from me to take the next step?

   Deeds, existing drawings, land registry extracts, the ITE if there is one. A first meeting should end with a concrete task for each side.

How Deurbe works in Bizkaia

Deurbe is a Bilbao-based architecture studio that has been designing and running work across Bizkaia since 1990. Depending on the scope, it takes on the initial analysis, the design, the technical documentation, the permits, the coordination of other professionals and site management. The team brings together architecture, building technology and interior design, with outside specialists when a commission warrants them.

The commissions have had very different scopes, which is exactly what is worth asking any studio. At Gorostiza Loft, in Barakaldo, the design resolved a site constrained by the road climbing to El Regato and the nearby Castaños river, and the building was eco-designed and audited with AENOR at both design and construction stage to an A energy rating. At the refurbishment in Arriluce, in Getxo, Deurbe took on site management and the modification of a project drawn up by other professionals, on a 1925 mansion.

That does not make Deurbe the answer to every commission, and a studio that says yes to everything should give you pause. You can see all architecture projects or the architecture page for Bilbao and Bizkaia before asking for a proposal.

The next step is to compare like with like

When you speak to several studios, give them the same information and ask them the same questions. That is the only way to compare experience, scope, team, cost and supervision on a common basis, rather than comparing the quality of the photographs or the gap between two final figures that cover different work.

If you do not yet know which stage you need, start by describing the property, the goal and the decisions already taken. Framing the commission is part of the job, and a serious studio should help you do it before committing to any solution.