Modular construction: what the regulations require

Why does the implantation time dictate everything else?

Modular construction produces buildings in the form of three-dimensional modules completed in a workshop, transported to the site, and then assembled. The process does not create any legal exceptions: it is the duration of the installation, and this duration alone, that dictates the planning formalities and the level of energy performance requirements. A project owner who considers the building as a "temporary structure" without verifying this duration risks having the project reclassified.

What distinguishes modular construction from prefabricated elements?

Prefabricated elements deliver flat components—precast walls, slabs, or structural panels—assembled into a structure on-site. Modular construction delivers volume: floors, walls, technical equipment, and finishes are integrated before transport. The difference, therefore, lies in what remains to be done on-site, and consequently in the degree of exposure to weather conditions and concurrent activities.

The trend is measurable within companies. In June 2025, the French Building Federation (FFB) reported on the case of the Blanchet group, a metal construction company, which increased its workshop production from 55% to 85% in ten years, and on the Aygalades-Oasis construction site, where 1,600 m² of prefabricated panels were used. The same publication points out the limitations of this approach: a purely modular approach carries a risk of architectural uniformity.

What planning permissions apply to a modular building?

Article R*421-5 of the Town Planning Code, in its version in force since September 25, 2023 , exempts from all formalities constructions erected for a period not exceeding three months . This is the standard legal regime for temporary structures, and it is short-term. Beyond that, the exemption only remains in specific cases, each with its own duration.

Upon completion, the builder must restore the site to its original condition. Apart from these cases, a module intended to remain in place falls under the standard regulations for new construction, requiring a building permit or prior declaration depending on the floor area and footprint created. Site installations, however, are subject to regulations related to the duration of the work.

Does the RE2020 regulation apply to modular construction?

Yes, unless the building remains within the scope of temporary constructions. The application sheet "Temporary constructions" of the portal for energy and environmental regulations for buildings, updated on March 14, 2025 , identifies three situations where adapted requirements replace the general regime: constructions installed for a period not exceeding two years within the meaning of article R*421-5 of the town planning code, demountable classrooms installed in schools or universities, and constructions necessary for carrying out works as well as installations related to the marketing of a building under construction.

These situations fall under Articles R. 172-2 and R. 172-4 of the French Building and Housing Code, which establish alternative requirements concerning building envelope performance, lighting management, heating and cooling regulation, and ventilation control. The provisions applicable to temporary structures have been in effect since July 1 , 2023 , and those for small buildings and extensions of less than 50 m² since ^{January 1} , 2023.

A module exceeding these limits falls under the full scope of the RE2020 regulation, with its Bbio, Ic construction, and degree-hour indicators. The practical consequence is simple: the usage time is determined by the program, not by the installation. Other regulatory benchmarks in the construction industry overlap on this point.

What standards govern the structure and its implementation?

Steel-framed modules fall under the NF EN 1090-1 standard , which requires manufacturers to provide a declaration of performance and CE marking for steel and aluminum structural elements, in accordance with European Regulation ^No. 305/2011 on construction products. The NF EN 1090 standard defines four execution classes, from EXC1 to EXC4 , with increasing requirements regarding traceability, welder qualifications, and non-destructive testing. The selected class determines the required workshop inspections: it is specified in the contract documents, not on the construction site.

Timber-frame modules follow a different set of standards, and their industrialization shifts control to the workshop, where the production of prefabricated timber walls is scaled up. The critical point, however, remains common to both sectors: airtightness and watertightness between modules, continuity of insulation, and load transfer. The connections between materials represent the majority of the technical risk in modular assembly.

What does prefabrication actually change in terms of lead times and preparation?

The time savings are well-documented. In June 2025, the French Building Federation (FFB) cited an operation completed in 8 weeks where traditional construction required 32 , a ratio of one to four. Furthermore, off-site fabrication removes some of the work from the weather, reduces waste, and limits construction site disruptions in urban areas.

The trade-off is a different kind of preparation. The same professional publication emphasizes the rigor required upstream and the coordination between stakeholders, with the digital model serving as a common tool. Decisions are finalized earlier: a modification requested after production has begun in the workshop is no longer treated as an on-site adaptation. The relevant professional organizations, UMGO , UMB-FFB , and EGF-BTP , are monitoring this shift in workload towards the design phase.

What happens to a module at the end of its use?

A modular building designed for dismantling retains a useful life after its initial use, but this does not exempt it from any regulatory requirements. A PEMD (products, equipment, materials, and waste) assessment is mandatory for demolition and significant renovation projects when the combined floor area of ​​the buildings concerned exceeds 1,000 m² , or when the building has housed an agricultural, industrial, or commercial activity involving hazardous substances.

The system stems from Law ^No. 2020-105 of February 10, 2020 , codified in Articles L. 126-34 and L. 126-35 of the French Building and Housing Code, and subsequently from Decrees ^No. 2021-821 and ^No. 2021-822 of June 25, 2021 , and the Order of March 26, 2023. For modular housing developments, the issue goes beyond mere formalities: it is the inventory that makes the reuse of modules feasible. It is essential to be able to identify each element years after its installation, which is made possible by the factory-applied component marking . Disassembly, however, is determined in the workshop, during the design phase.