When is an architect required in France? The 150 m² rule
An individual building for themselves only needs an architect above 150 m² of floor area (surface de plancher). But the calculation, extensions and companies follow precise rules.
The principle: no building permit without an architect
The French law on architecture of 3 January 1977 sets a general rule: anyone applying for a building permit (permis de construire) must have the architectural design drawn up by an architect registered with the Ordre des architectes.
It then sets the exception that matters most to homeowners: an individual who builds or alters a small building for their own use does not need one. Interior works that leave the outside unchanged are also exempt.
The 150 m² floor-area threshold
Since 1 March 2017, "small" means 150 m² of surface de plancher (article R*431-2 of the Code de l'urbanisme). Only the floor area counts for this threshold, not the building's footprint (emprise au sol).
Surface de plancher adds up all enclosed, covered floor areas with a ceiling height above 1.80 m, measured inside the walls, after a few deductions (stairwells, parking, attics that cannot be converted, and so on).
Above 150 m² of floor area, an architect must sign the building permit design. Below it, an architect is recommended but not compulsory. A déclaration préalable (prior declaration) never requires an architect.
Extensions: the total after works counts
For an extension that needs a building permit, the existing floor area and the extension are added together:
| Situation | Architect required? |
|---|---|
| 120 m² house + 25 m² extension (145 m² in total) | No |
| 130 m² house + 30 m² extension (160 m² in total), permit needed | Yes |
| 170 m² house + any extension that needs a permit | Yes |
| Extension that only needs a prior declaration | No |
In the urban zone of a local plan (PLU), an extension of more than 20 m² that takes the total above 150 m² needs a building permit, and therefore an architect. The house extension guide covers these cases.
Companies and SCIs: always an architect
The 150 m² exception only applies to individuals. A company, including a family property company (SCI), must use an architect for any building permit, whatever the size. Only farm businesses are exempt. Joint owners (indivision) are not a company, so the individual thresholds apply.
Other cases: farms, greenhouses, housing estates
- Farm buildings: an architect becomes compulsory once the floor area or the footprint exceeds 800 m².
- Commercial greenhouses: no architect while the posts are under 4 m high and both floor area and footprint stay within 2,000 m².
- Change of use needing a permit (because it alters load-bearing structures or the façade): architect above 150 m².
- Housing estates (lotissements): above 2,500 m² of land, the plan for the permis d'aménager must be drawn up by an architect or a landscape designer (paysagiste-concepteur).
Below 150 m²: why use an architect anyway
Even when it is optional, an architect brings a design suited to the site and budget, a permit application that stands up to the local plan's rules and, with a full mission, site supervision. You can also hire one for the permit application alone, for a fixed fee. Before deciding, the CAUE in your department can advise you for free.
The official rule is summarised on service-public.gouv.fr (in French).
Frequently asked questions
From what size is an architect compulsory in France?
For an individual building for themselves, above 150 m² of floor area (surface de plancher), counting the total after works for an extension. A company or SCI must always use an architect for a building permit.
Do I need an architect for a déclaration préalable?
No. The obligation to use an architect only applies to projects that need a building permit.
Does the footprint (emprise au sol) count towards the 150 m²?
No. Since 1 March 2017 only the floor area (surface de plancher) counts for this threshold.
Can an SCI build without an architect?
No, unless it is a farm business. Every company, SCIs included, must use an architect for a building permit, whatever the size.