Building a data center: the stages, the lead times and the main difficulties

Stage 1 — Choosing the site

Everything starts with three criteria, in this order:

1. The available power and the connection lead time (see Access to power, the new bottleneck for data centers).
2. Land: area, buildability, natural hazards, proximity to fibre.
3. The environment: water resources, neighbours, potential for heat reuse.

Large operators now favour brownfield industrial sites and zones identified by the State, but AI campuses covering several dozen hectares sometimes struggle to find land that is already developed.

Stage 2 — Design

Design sets the target level of availability, often expressed using the Uptime Institute Tier classification:

In practice, design organises the electrical chain (high-voltage intake, transformers, switchboards, UPS, batteries, generators), the thermal chain (cooling production, distribution, data hall cooling), fire safety, the building management system and security. For AI sites, liquid cooling adds hydraulic networks right into the racks (see Liquid cooling, immersion: the innovations changing how data centers are built).

The BIM digital model has become a central tool: it makes it possible to coordinate thousands of services in very tight spaces and to prepare for operation.

Stage 3 — Obtaining permits

A data center is generally a classified installation for environmental protection (ICPE) under French law, in particular because of its generators and fuel oil storage. Depending on its size, it needs an environmental impact assessment, a public inquiry, an environmental authorisation and a building permit. Large projects can now be classified as projects of major national interest, which speeds up some procedures (see Public policy: what the State and the regions are doing to attract data centers). Legal challenges, which are increasingly frequent, can add months or even years.

Stage 4 — Construction

The works involve many trades: earthworks, civil engineering, structural frame, roofing, then above all the MEP packages. On a data center, the share of the electrical and HVAC packages in the construction budget is much higher than on an office building.

Campuses are built in phases: a first building is handed over while the next ones are under construction. Operators increasingly use prefabrication (electrical modules, plant rooms, cooling units assembled in the factory) to save time and secure quality. This is the purpose of the power module factory that SoftBank and Schneider Electric plan to set up in Dunkirk.

Stage 5 — Commissioning

This is the phase most specific to data centers. It generally takes place in five levels, from factory acceptance of the equipment through to integrated tests of the whole site. During the final tests, power cuts and failures of chillers or generators are simulated, with load banks that reproduce the heat of the servers. The goal: to prove that the site delivers on its availability promises before the first customer moves in.

Stage 6 — Operating and evolving

Once in service, the site runs continuously, 24 hours a day. Data halls are filled gradually, and equipment evolves with each generation of servers. A well-designed data center anticipates these changes: power reserves, the option to switch to liquid cooling, extension of the heat network.

The five most common difficulties

1. Grid connection, often the longest item in the schedule.
2. Lead times for major equipment (transformers, generators, high-voltage switchboards), which can exceed a year.
3. Local acceptance and legal challenges (see Data centers and the environment: water, land and local acceptance).
4. Interfaces between packages and between players (operator, end client, project management, contractors, RTE).
5. Skills: project managers and electrical, HVAC, commissioning and BIM engineers who have already delivered critical sites are rare (see How many engineers will it take to build tomorrow's data centers?).