The short answer
It depends on the type of work. Under the LOE, the project for a new home, or for work on its structure, is signed by an architect. An interior renovation with no structural change and no change of use can in many cases be signed by an arquitecto técnico (aparejador, roughly a building surveyor). Projects for certain installations above a given power are signed by an engineer, and electrical and gas certificates are issued by a licensed installer.
The exact boundary between these roles depends on the specific job and the permit regime; in doubtful cases it is confirmed with the professional colegio or the ajuntament. Here is how it works in practice.
Why the signature matters
Signing a project or certificate carries personal professional liability. The technician is insured, registered with a colegio and answers for what they sign. The ajuntament only accepts documents from someone with the right qualification.
If someone without the competence signs, the consequences show up later: the permit is revoked, the cédula de habitabilidad is not issued, the utility will not connect the extra power, or the buyer of the flat finds the problem in the paperwork. Fixing it means a new project and new costs.
Who answers for what
Architect. Projects for a new home, an extension, an extra storey, structural changes or a change of use. Often also heads the site direction.
Arquitecto técnico (aparejador). Renovation projects with no structural work, direction of execution, quality and safety control on site. On a house build they work alongside the architect.
Engineer. Projects for specific installations: heating, cooling and ventilation above a certain power, electrics for commercial premises, special installations. On clinics and commercial units their signature is common.
Licensed installer. Does not design, but issues the official certificate for the completed electrical or gas installation. Without it, the utility will not connect extra power.
What it looks like on real projects
A finishes-only renovation of an Eixample flat with no walls moving often needs no project at all: the council notification and the installer's certificate for the new wiring are enough.
A full renovation that moves partitions and bathrooms does require technical documentation, signed by someone with the right qualification.
The 250 m² child psychology centre in Eixample, which we ran from January to June 2026, is an example with many signatures: besides the fit-out there was heat-recovery ventilation and air conditioning, plus the legalisation of the healthcare activity. Each part needs its own professional, and fitting them into one programme is a job in itself.
The house with a pool and solar panels built between 2022 and 2024 went through the full cycle: an architect's project, site direction and separate certificates for each installation.
How to check the professional
Ask for the name, qualification and colegio registration number. Architects in Catalonia belong to the COAC, arquitectos técnicos in the province of Barcelona to the CAATEEB, and engineers to the colegio for their field. The colegios' websites usually let you check that the person is registered.
Ask about professional liability insurance. A practising professional has it and will confirm it without fuss.
Notice who signs and who actually does the work. It is normal for a team to prepare the drawings, but the signature and the liability rest with one specific person entitled to sign.
Whose side the technician is on
The site direction team checks that the work follows the project and the rules. If the architect or aparejador is hired by the builder, ask plainly how the relationship works: who pays their fee, who they report to, and whether they can stop the work if something is done wrong.
That arrangement is possible and common, especially in flat renovations. What matters is that you know who the person is, how to reach them and what they sign on your behalf as the client.
What the quote should show
If the work needs a project or technical documentation, the quote should include a line for professional fees and processing. If that line is missing when you are planning to move walls, ask who is going to sign and who is paying for it.
We put the technical team together to suit the project: no more people than needed, but no gaps either. The permit regime and required signatures are established at the site visit, before the quote. Each project has one person in charge, in Russian or Spanish, with staged payments under the contract. We reply to enquiries within an hour.