Prior declaration, building permit, local urban plan (PLU): what governs the installation of a modular home on a plot of land, and who takes care of it.
An AIIA home is designed, built in the workshop and then delivered to your land; installation is carried out by the installer of your choice, whom we can recommend. But before the home arrives on site, one question comes up every time: which administrative formalities need to be completed, and who takes care of them? This article sets out the general principle and points to the competent authorities: it is in no way a substitute for the opinion of your town hall, and it does not constitute legal advice.
Do you need planning permission to install a modular home?
In most cases, yes. Like a conventional building, a modular home requires no formality, a prior declaration or a building permit, depending on the floor area created and, for a non-permanent installation, how long it stays.
As our Regulations and installation page points out, and as we already explain in “Turnkey modular home: what is included” (section “The limits to know before you start”), the home offer and the land remain two separate scopes. Every plot is different, every municipality applies its own rules, and it is this second scope that this article covers in detail.
Under French planning law, a new construction requires, depending on the case, no formality at all, a simple prior declaration of works, or a building permit. What determines the applicable regime is not whether a home is modular or built on site: it is the area created (floor area or ground footprint) and, for non-permanent installations, their duration. Service-Public.gouv.fr, the official portal of the French administration, devotes its information sheet “Déclarer préalablement des travaux” (reference F17578, updated and checked on 19 October 2026) to this question: it confirms that a prior declaration is mandatory for works that create floor area or ground footprint without falling under a building permit, and refers to Articles R. 421-9 to R. 421-12 of the French Planning Code for new constructions, and to Article R. 421-17 for works on an existing construction. The regime for temporary constructions (Article R. 421-5 of the same code) is also mentioned, although the sheet does not itself detail its conditions; this is a point to check directly with the planning department for any installation that would not be permanent.
From what floor area is a prior declaration required?
Local planning departments place the thresholds around 5 m² and 20 m² of floor area or footprint, up to 40 m² for some extensions in urban areas covered by a local plan (PLU). Only your town hall confirms the threshold that applies.
In its directly accessible text, this official sheet does not publish the area thresholds expressed in m². The planning departments of several local authorities that were consulted nevertheless place these thresholds, for a new construction, at around 5 m² and 20 m² of floor area or ground footprint, below which no formality applies and up to which a simple prior declaration applies, it being specified that a different threshold (up to 40 m²) may apply in certain cases of extension of an existing building in an urban zone covered by a local urban plan (PLU). These figures are not taken from the national Service-Public.gouv.fr sheet itself: they come from local planning departments, they are consistent with one another, but they may vary according to the specific rules of each PLU. Only the planning department of your town hall can confirm the threshold that actually applies to your project.
The municipality's local urban plan (PLU) is the document that, in practice, decides what is possible on a given plot: zoning, rules on height or siting, protected areas where stricter rules may apply. Two neighbouring plots located in two different zones may therefore fall under different regimes for the same project. That is why, beyond the general regulations, the feasibility of an AIIA project also depends on the accessibility of the land for transport and installation, and on the regulations applicable to the project's area: this is precisely what our site study, carried out on request, checks before any manufacturing begins, a step we recommend requesting early, in parallel with the checks made with your town hall, and not afterwards.
Who handles the paperwork?
The buyer. AIIA designs the home, has it built in the workshop and delivers it; the planning application, the plot and the utility connections remain your responsibility.
One point remains constant, whichever model is chosen from our catalogue: the administrative formalities (prior declaration or building permit, depending on the area) remain the buyer's responsibility. AIIA designs your home, has it built in the workshop, transports it and delivers it to your land, where your installer installs it; however, filing the planning application at the town hall is not a service provided by AIIA, just like the land itself or the connections to public networks (water, electricity), which need to be arranged with a local professional, in coordination with our team for the delivery schedule. This division follows the same logic as the one set out in “Turnkey modular home: what is included”: “turnkey” describes the level of completion of the home itself, not responsibility for the land and its formalities. Before committing, a few points should be clarified directly with your municipality's planning department: which formality actually applies to your project given its exact area and the zoning of your PLU; whether your land lies in an area subject to particular rules (protected zone, surroundings of a historic monument, housing estate with its own regulations); the period of validity of the document obtained (a prior declaration, for example, is valid for three years and lapses if works have not started within that period, or if they are interrupted for more than a year); and the specific case of a non-permanent installation, for which a separate regime may apply (Article R. 421-5 of the French Planning Code), to be confirmed case by case.
There is no single regime applicable to “a modular home”: everything depends on the project's area, on how long it will stay in place where relevant, and on your municipality's PLU. AIIA takes care of the design of your home, has it built in the workshop and transports it to your land, where your installer installs it; the administrative formalities, the land and its utility connections remain on your side, in liaison with your town hall and the relevant local professionals. Our Regulations and installation page covers these questions in the form of short answers, and our team remains available for any question about the feasibility of your land, without ever taking the place of your town hall's opinion.
Why check planning rules before manufacturing?
Because planning rules determine whether the project is feasible. Our site study, on request, checks them before any manufacturing.
Frequently asked questions
Does a modular home need a building permit?
Not always. Depending on the floor area created, how long it stays and your town's local plan (PLU), it requires no formality, a prior declaration or a building permit. Your town hall's planning department confirms which applies.
How long is a prior declaration valid?
Three years. It lapses if work has not started within that period, or if it is interrupted for more than a year.
Does AIIA file the planning application with the town hall?
No. Filing the application remains the buyer's responsibility, like the plot and the utility connections. Our site study, on request, helps you prepare these checks.
Do temporary installations follow the same rules?
A separate regime may apply to non-permanent installations (Article R. 421-5 of the French Planning Code). It is confirmed case by case with the planning department.
Frequently asked questions
Does a modular home need a building permit?
Not always. Depending on the floor area created, how long it stays and your town's local plan (PLU), it requires no formality, a prior declaration or a building permit. Your town hall's planning department confirms which applies.
How long is a prior declaration valid?
Three years. It lapses if work has not started within that period, or if it is interrupted for more than a year.
Does AIIA file the planning application with the town hall?
No. Filing the application remains the buyer's responsibility, like the plot and the utility connections. Our site study, on request, helps you prepare these checks.
Do temporary installations follow the same rules?
A separate regime may apply to non-permanent installations (Article R. 421-5 of the French Planning Code). It is confirmed case by case with the planning department.
