A data center in France is not permitted through a single file. It needs at least two, handled by two different authorities: the building permit, usually issued by the mayor, and the classified installations regime (ICPE, installations classées pour la protection de l'environnement), which falls under the prefect and is reviewed by the regional environment authority (DREAL). One can be granted without the other, and both are needed. That is the first source of delays and litigation.
DOES YOUR SITUATION LOOK LIKE ONE OF THESE?
1. THE BUILDING PERMIT
Who decides. In principle, the mayor or the inter-municipal authority. Since the law of 26 May 2026, however, a data center designated by decree as a "project of major national interest" has its permit issued by the prefect. In the Paris region, a prefectoral approval is also required above 5,000 m² of floor area, before the permit itself.
What the local plan says. Since an order of 22 March 2023, data centers fall under the "warehouse" sub-use. Zoning can therefore block a project: in June 2025, the Lyon administrative court upheld a permit refusal at Irigny, ruling that a data center was not a public-interest facility allowed in that zone.
Technical equipment counts. At Wissous (Essonne), adding a backup generator, a fuel tank and two delivery substations required an amended permit, which the town refused in 2021. It took until the Versailles administrative court of appeal ruled in October 2025 to unblock it. Generators, tanks and substations are part of the planning file.
Water. The law of 26 May 2026 also allows a data center permit to be refused in an area with structural water stress.
2. CLASSIFIED INSTALLATIONS (ICPE) AND THE DREAL
There is no "data center" item in the classified installations nomenclature. The regime depends on the equipment: combustion plants for generators, fuel storage, refrigerants for cooling. For combustion, what counts is the total thermal input of the site, not its electrical output. The thresholds usually cited are: declaration from 1 MW thermal, registration between 20 and 50 MW, full authorisation above.
The three regimes have very different timelines. A declaration is quick. Registration is a simplified authorisation. A full environmental authorisation often takes more than a year, with an impact assessment, a hazard study and a public inquiry. Courts keep the regimes apart: at Wissous, the court refused to treat an installation subject to registration as one subject to authorisation. Once an authorisation is granted, third parties have two months to challenge it.
Key point: the environmental authorisation covers equipment that is functionally necessary to the project, or whose proximity changes its hazards. The prefect looks at the site as a whole, not item by item.
3. THE PHASING TRAP
Two recent decisions show where the line lies.
Alixan (Drôme), July 2026. The Grenoble administrative court suspended a data center permit in summary proceedings. It held that the project's two phases and its backup generators formed a "functional unit", hence a single project. Taken as a whole, it exceeded 50 MW and should have had an impact assessment before the permit. The decision is provisional, pending the ruling on the merits.
Wissous (Essonne), April 2026. Conversely, the Versailles court of appeal accepted a split into three phases, because each operated independently and the registration covered the first two. It added that the third phase, above 50 MW combined, would require a full environmental authorisation for the whole site.
Phasing a project is legitimate. Splitting it to stay below a threshold is not, and the courts check.
4. WHAT ABOUT TEMPORARY POWER?
More and more projects plan a temporary power solution, containerised gas or diesel generators, to start before the permanent grid connection arrives. The framework is poorly understood, and many players move forward without certainty. The questions to settle are:
For how long? The exemption from formalities only covers short-term installations
Is a temporary ("precarious") permit possible, and who issues it?
Is the solution part of the data center project, and does its output add to the site's?
Who files and who operates: the power provider or the data center?
How to obtain a clear position from the authorities before committing?
The answer depends on each configuration. But the Alixan ruling makes one assumption prudent: a solution that powers a data center may be considered part of the same project. Better to know before ordering the generators.
5. THE METHOD THAT AVOIDS SURPRISES
List all equipment early, including backup and temporary power, and derive the regime of each file.
Keep the files consistent: the permit and the environmental file must describe the same project, with the same scope.
Meet the authorities upstream: the DREAL and the prefecture for classified installations, the town or inter-municipal authority for the permit.
Explain the project to elected officials and residents before filing: what it brings to the area, what is temporary and what is not, how noise, water and emissions are controlled. A project that is understood is less exposed to challenges.
See also our article on data center permit challenges and our opposition tracker.
Sources: French Planning Code (articles L. 421-1, L. 300-6-2, L. 422-2, R. 510-1); Environmental Code (articles L. 181-1, L. 512-1, L. 512-7, L. 512-8); order of 22 March 2023 on building sub-uses; law no. 2026-403 of 26 May 2026 (article 35); Versailles administrative court of appeal, 8 October 2025, nos. 23VE02040 and 23VE02041, and 2 April 2026, no. 25VE01156; Grenoble administrative court, 10 July 2026, no. 2605946; Lyon administrative court, 3 June 2025, no. 2306531; DCmag, 15 October 2026. Classified-installation thresholds must be checked item by item in the version in force. This article is general information, not legal advice.
FREQUENTLY ASKED QUESTIONS
Is a data center a classified installation (ICPE) in France?
There is no "data center" item. Its equipment, especially backup generators (combustion), fuel storage and refrigerants, places it under declaration, registration or full authorisation.
Who handles data center permits in France?
The building permit is usually issued by the mayor or inter-municipal authority, or by the prefect for a project of major national interest. Classified installations fall under the prefect, reviewed by the DREAL.
How long does a full environmental authorisation take?
Often more than a year, with an impact assessment, a hazard study and a public inquiry. Declaration and registration are much faster.
Does temporary power need a permit in France?
It depends on the configuration: type of installation, duration, local plan, combined output with the site and link to the project. Beyond a short period, a planning formality is usually needed, and the output may add to the data center's.