Conservatory and planning permission: what you need to know before taking the plunge

The installation of a conservatory constitutes a modification of the external appearance of your home and an extension of its floor area. As such, it is subject to town planning rules defined by the Code de l'urbanisme and local documents such as the PLU (Plan Local d'Urbanisme).

Here are the main scenarios:

• Conservatory up to 5 m²: no authorization required.
• Between 5 m² and 20 m²: a declaration préalable de travaux is required.
• Between 20 m² and 40 m²:
• In zones not covered by a PLU: permis de construire obligatoire.
• In zones covered by a PLU and if the total surface area of the house remains less than 150 m²: prior declaration sufficient.
• Over 40 m² or if the house exceeds 150 m² after work: mandatory building permit + use of an architect.

These thresholds concern the floor area or the footprint created by the conservatory. It is therefore crucial to measure the exact surface area projected.

Other points to consider:

• The construction of a conservatory must respect local rules (alignment, setback, height, color of joinery...).
• In safeguarded areas or classified zones, specific authorizations may be added.
• A conservatory must not encroach on the right of view or neighborhood.

📚 Main source : Service-Public.fr, fiches pratiques urbanisme et permis de construire.

Once the type of authorization has been determined, it's time for the formalities. Here are the steps to follow so that your conservatory project is compliant and validated without any nasty surprises.

1. Déclaration préalable de travaux

This is a simplified procedure designed for small-scale projects. The dossier to be submitted to the town hall must include:

• the completed form Cerfa n°13703*08,
• a plan de masse,
• a plan de situation,
• visuals of the final appearance.

⏳ Investigation time: 1 month. In the absence of a response from the mayor's office after this deadline, authorization is considered granted.

2. Permis de construire

Required for larger conservatory or in areas subject to constraints. The file includes:

• the form Cerfa n°13406*12,
• a detailed description of the project,
• dimensional drawings,
• sometimes a thermal study if the conservatory is heated.

⏳ Instruction time: 2 to 3 months depending on the commune.

In both cases, the authorization must be posted on the site for the duration of the works.

👉 To maximize your chances of acceptance:

• Use a professional (installer, architect, design office) who will be able to put together a compliant technical file.
• Check local constraints (PLU, easements).
• Integrate aesthetic and energy-saving solutions (double glazing, sober and colored aluminum profiles, etc.).

Many conservatory projects are slowed down, or even called into question, because of an administrative oversight or an incomplete file. A few simple reflexes can help you secure your approach.

To avoid unpleasant surprises:

• Never start work without authorization. In the event of an inspection, you risk a fine, site suspension or even an obligation to demolish.
• Don't underestimate the surface area: a roof overhang or a pillar can tip your project into the "building permit" category.
• Always consult the PLU of your commune. Some zones impose rules on materials, colors or the orientation of the conservatory.
• Take the neighborhood into account. Respecting distances, views and sunlight are elements taken into account in any appeals.
• Post the authorization legibly (regulatory sign visible from the public highway).

Using an Installux partner professional has several advantages:

• He knows the local regulations and technical constraints.
• It helps you optimize the design to maximize light, comfort and integration.
• It puts together a complete dossier, often more quickly accepted by planning departments.

Finally, be aware that some conservatory projects can be part of a logic of thermal improvement, opening the right to grants or VAT at a reduced rate (10%) if the conditions are met.