Converting commercial premises into a home has become one of the most common property operations in Madrid. Spain’s Supreme Court has just laid down binding case law on who may sign that project, and in doing so it has shifted the ground under a good number of ongoing deals. We explain, without embellishment, what the Court decided, which buildings it actually affects and what you should check before filing for your permit.
1. What the Supreme Court actually decided
Judgment no. 700/2026 of 4 June, handed down by the Administrative Chamber of the Supreme Court, dismisses the cassation appeal brought by the Official Association of Technical Architects of Málaga against the judgment of the High Court of Justice of Andalusia of 8 July 2022.
The underlying case was straightforward. A private individual applied for a permit to convert business premises into a dwelling inside a building erected for commercial and industrial uses, submitting a project signed by a technical architect. The town council required the signature of a fully qualified architect. The professional association challenged that decision and lost at every instance, up to the Supreme Court.
The binding doctrine set out by the Court in the Fourth Legal Ground reads as follows:
“Article 10.2 a) of Act 38/1999 of 5 November on Building Regulation, read together with articles 2.1 a) and 2 b) and article 4 of that same Act, must be interpreted as meaning that works projects concerning interventions on existing buildings which alter their architectural configuration, or whose purpose is to change the characteristic uses of a building from commercial to residential, must be drafted by a fully qualified architect.”
In practical terms: if the building housing your premises has a commercial or industrial characteristic use, the project for a change of use from commercial premises to dwelling must be drafted by an architect. Size is irrelevant — a single unit within that building is enough to trigger the rule.
2. Why the LOE is the decisive statute
Everything turns on Act 38/1999 on Building Regulation (the LOE), which allocates professional competence according to the building’s use and the type of works.
- Article 2.1(a) LOE. Places “residential use in all its forms” in group (a), alongside administrative, healthcare, religious, educational and cultural uses.
- Article 2.2(b) LOE. Treats as building works — and therefore as requiring a project — “all interventions on existing buildings, provided they alter their architectural configuration”, which includes those “whose purpose is to change the characteristic uses of the building”.
- Article 10.2(a) LOE. For buildings in group (a) of article 2.1, the qualifying degree for the project designer is that of architect.
The Court’s reasoning links those three provisions: converting business premises into a dwelling inside a commercial or industrial building is not minor work, because it directly affects “the technical requirements and conditions of habitability, safety and functionality of part of the building, and may have an impact on its overall structure”. The Court adds that this conclusion is consistent with the principles of necessity and proportionality in articles 5 and 17 of Act 20/2013 on Market Unity: the point is not to protect a profession, but to require the qualification suited to the technical risk being assumed.
3. The limits of the ruling: which buildings it affects and which it does not
This is where oversimplifying is dangerous, because the headlines circulating this summer are broader than the judgment itself.
3.1. Buildings whose characteristic use is commercial or industrial
This is the scenario actually decided and the only one the doctrine covers unambiguously: offices, warehouses and commercial buildings converted, wholly or partly, to residential use. Here the project designer must be an architect.
3.2. Ground-floor premises in a residential block
This is by far the most common situation on the market: premises in a block of flats converted into one more dwelling. The technical architects’ professional bodies — including the one that was a party to the proceedings — argue that the judgment does not reach this scenario, because the building’s characteristic use is already residential and remains unchanged. The Superior Council of Associations of Architects of Spain favours a broader reading, stressing that exclusive competence is triggered even where the change affects only one of the units making up the building.
Our own reading, feet on the ground: the judgment deals with a commercial and industrial building and its doctrine is drafted around that scenario. But permits are granted or refused by the town council, not by a professional association, and some municipal technical departments are applying the criterion expansively. Until a ruling narrows the scope, filing a change-of-use project signed by a technical architect carries a real risk of formal objection and delay. If your deal runs to a tight timetable — a conditional purchase, financing, a committed lease — that risk has a price.
4. The consequence almost nobody is discussing
There is a second effect of the ruling, less commented on and more relevant to the owner: by requiring an architectural project, the Supreme Court brings the intervention within the scope of the LOE. That reaches well beyond who signs the drawings.
- Three agents are now required. Project designer, works director and works execution director. A technician signing a document for the town council is no longer enough.
- The liability regime of article 17 LOE is triggered, with guarantee periods of ten, three and one year depending on the type of defect, together with the guarantee system of article 19, whose specific application must be assessed case by case.
- Costs rise and timescales lengthen. Industry sources put the increase in professional fees at between 30% and 50% compared with a technical architect’s signature, on top of the additional time for professional vetting and processing.
For an investor working on tight margins over portfolios of dated premises or offices, this is not a formality: it changes the numbers. If your building also carries maintenance obligations, it is worth cross-checking against our guide to the Building Technical Inspection in Madrid.
5. Does the community of owners have a say?
This is always the next question, and it should be kept separate from the above, because the two operate on different planes.
Under settled Supreme Court case law, an owner may change the intended use of their private unit — from commercial premises to dwelling — unless there is an express prohibition or restriction in the deed of horizontal division or in the community by-laws. The mere description of the property as “premises” in the Land Registry does not in itself amount to a prohibition. For the restriction to be enforceable against third parties it must also be registered at the Land Registry.
The position is different where the works affect common elements: a new service connection, ventilation or fume extraction through the façade or courtyard, structural reinforcement, opening new apertures. There, a resolution of the owners’ meeting is required, by the majority laid down in the Horizontal Property Act. It is also worth reviewing how expenses are shared: as we explained when analysing exempt commercial units and accessibility works, moving from commercial premises to dwelling can change an owner’s position vis-à-vis the community.
On top of all that, in Madrid there is a prior planning filter: compatibility of uses under the local plan, minimum usable floor area, clear ceiling height, natural ventilation and daylight, and the requirements of the Spanish Technical Building Code. A change of use that looks viable on paper can be unviable on the particular plot.
6. Practical cases
Office floor in a tertiary building in the city centre. A client buys an office floor in a building whose characteristic use is commercial, intending to divide it into three dwellings. The doctrine applies squarely here: an architect’s project, with works direction and works execution direction. We would recommend building a condition precedent tied to obtaining the permit into the purchase contract, because processing costs have shifted upwards.
Ground-floor premises in a residential block. The building’s characteristic use is residential, so on the technical architects’ reading the judgment does not reach it. Even so, before commissioning the project it is worth checking the position of the municipal technical department: if the council applies the broad reading, a project signed by a technical architect means a formal objection and months lost.
Industrial warehouse acquired in 2025 with a project already vetted. If the project is signed by a technical architect and the permit is still pending, the prudent course is to review the file before the objection arrives, consider replacing the technician and recalculate the impact on the timetable. Acting before the objection is usually cheaper than responding to it.
Summary: the key points
- Supreme Court judgment 700/2026 of 4 June lays down binding doctrine: change of use from commercial premises to dwelling in buildings whose characteristic use is commercial or industrial requires a project drafted by an architect.
- The legal basis is articles 2.1(a), 2.2(b), 4 and 10.2(a) of the LOE.
- The judgment does not expressly resolve the case of premises located in an already residential building, which is the most frequent scenario. The debate remains open and the practical decision rests with each town council.
- Once the intervention falls within the scope of the LOE, a project designer, a works director and a works execution director are required, and the liability regime of article 17 LOE is triggered.
- The estimated increase in project costs is between 30% and 50%, with longer timescales.
- The community of owners can only block a change of use where there is an express prohibition in the deed of horizontal division or the by-laws; works affecting common elements are a separate matter.
- Before buying: an individual planning viability study and a review of the deed of horizontal division. After buying, your room for manoeuvre is far narrower.
Do you need advice on a change of use?
At Quikprokuo we have spent more than twenty-five years advising owners and investors on urban planning permits and changes of use and on property purchase and sale transactions in Madrid. If you are considering converting commercial premises or an office into a dwelling, or you have a file in progress that this judgment may affect, let us review your case before the town council reviews it for you.
Get in touch and we will tell you plainly whether your operation is viable and what it will take to see it through.
