Prior Declaration, Building Permit, Mandatory Architect: The Steps in Paris

Before the first hammer blow, a Paris renovation is already being decided on paper. The question is never “am I allowed to carry out this work?” but rather “which authorisation do I need, and which one is enough?” Because behind an apparently straightforward project, removing a partition, changing windows, converting premises into a home, lies a whole scale of formalities. When a simple declaration is enough, and when more is required: that is precisely the line this guide sets out to draw.

In Paris, that line is stricter than elsewhere. Almost the entire capital is covered by heritage protections, and a significant proportion of buildings sit within the perimeter of historic monuments. The result: façade cleaning, replacing joinery or altering an elevation, works that might pass unnoticed in the countryside, can require approval from an architecte des Bâtiments de France. Understanding these rules in advance is not mere paperwork: it is how you avoid a stopped site, an enforced reinstatement, or a sale blocked years later.

In brief

• No formalities for routine maintenance and interior decoration, provided there is no structural alteration and no change to the exterior appearance.
• Prior declaration (DP) for minor works: façade alterations, replacement joinery, modest surface-area creation, change of destination without work on the structure.
• Building permit (PC) for larger projects: substantial creation of floor area, works affecting the load-bearing structure, change of destination with alteration to the façade or structure.
• Architect mandatory once the property’s total floor area exceeds 150 m² after works (for a private individual).
• In Paris, almost everything visible from the outside falls within the remit of the Bâtiments de France opinion.

Indicative benchmarks 2026: thresholds and procedures change, so always check with the City’s planning department before filing.

Prior declaration or building permit: where the line is drawn

Two planning authorisations structure most renovation projects: the prior declaration of works and the building permit. The first is a lighter procedure; the second is a full application. Knowing which category your project falls into is the very first decision to make.

The prior declaration (DP)

The DP applies to works of limited scope that nevertheless alter the building or its appearance. It is typically filed to:

• alter the exterior appearance: change windows, install a different guardrail, create or infill an opening, replace an entrance door onto the street;
• create a measured amount of floor area: a modest extension or upward addition, within the limits set by the French planning code;
• change the destination of premises without touching either the façade or the load-bearing structure;
• renovate a façade, an operation which, in Paris, is almost always subject to authorisation.

The file is lighter than a permit application, but it is not insignificant: drawings, photographs, how the project fits into its surroundings, and a descriptive note. An incomplete file will extend the timeline accordingly.

The building permit (PC)

A permit is required as soon as the project becomes more substantial or affects the soundness of the building. You move into this category in particular when you:

• create a significant amount of floor area beyond the prior declaration thresholds;
• alter the building’s load-bearing structures while also changing the use of the premises;
• change a property’s destination with works to the façade or structure.

The review process is longer and more demanding. Inside an apartment, most changes to the layout of rooms in fact fall under a prior declaration, or even require no planning formality at all, the focus then shifts to the co-ownership, a subject we cover in a dedicated guide. The permit, by contrast, mainly concerns heavy operations and the creation of floor area.

Surface-area thresholds and mandatory use of an architect

This is the most common confusion: assuming that “bringing in an architect” and “filing for a permit” are the same thing. They follow two distinct logics.

Using an architect is mandatory by law when, after works, the total floor area of the construction exceeds 150 m² for a private individual. Below that threshold, you may design and file your application without a qualified architect, which of course does not remove the need for design expertise.

A few reference points for getting it right:

• Floor area is calculated inside the walls, under sufficient ceiling height; it differs from the Carrez area used in property sales.
• The threshold is assessed on the total after works, not only on the area created. A property already close to 150 m² can tip over the line with just a few additional square metres.
• The architect threshold and the building permit threshold do not coincide: depending on the exact nature of the project, you may need a permit without an architect, or an architect without a permit.

Worth remembering: for a typical Paris apartment renovation, with no major creation of floor area, the question of a mandatory architect often does not arise. It becomes central as soon as there is an extension, an upward addition or the joining of lots that takes the whole beyond 150 m².

Protected areas and Bâtiments de France: the Paris particularity

This is where Paris changes everything. Elsewhere, a prior declaration may be examined by the local authority alone. In the capital, the omnipresence of heritage adds an essential interlocutor: the architecte des Bâtiments de France (ABF).

When the Bâtiments de France opinion is required

Its opinion is required whenever your project is visible from, or located in the surroundings of, a historic monument, or falls within a site patrimonial remarquable (protected heritage site). In Paris, this covers a very large part of the city. In practical terms, this includes:

• the replacement of joinery on the street side (material, colour, design, division of panes);
• any façade alteration: colour of a façade renovation, ironwork, shopfronts, guardrails;
• visible roof interventions: dormers, roof windows, roofing materials;
• the elements that define the identity of a haussmannien building, whose overall coherence is precisely what the protection seeks to preserve.

The most tightly regulated districts

Certain neighbourhoods fall within a secteur sauvegardé, now integrated into the regime of sites patrimoniaux remarquables, with particularly detailed rules that may extend even to interior arrangements: staircases, decorative features, original layouts. The Marais is the best-known example. Within these perimeters, the ABF opinion is not just one more formality: it can guide choices of materials, colours and execution from the design stage.

The mistake to avoid is treating this opinion as an obstacle. Anticipated properly, it can be prepared for: by documenting the existing condition and proposing solutions that respect the original aesthetic, a constraint becomes a mark of quality, and you avoid the refusal that sends everything back to the beginning.

Change of destination

Converting a former caretaker’s lodge, commercial premises, a workshop or a chambre de service into a home, or the reverse, falls under a change of destination. The planning code works by broad categories of use (residential, retail, office, etc.), and moving from one to another is a regulated act.

The general rule:

• a change of destination without works to the load-bearing structure or façade falls under a prior declaration;
• a change of destination accompanied by works affecting the structure or façade moves into building permit territory.

In Paris, a specific and often decisive layer is added: the protection of housing. Converting a dwelling to another use runs up against strict municipal rules designed to preserve the capital’s housing stock. Before any project of this kind, including certain short-term rentals, it is essential to check the applicable regime: this is one of the areas where a misjudgement can prove most costly.

Timelines and administrative pitfalls

A planning authorisation is not just a box to tick: it is a schedule to build into the project. Underestimating it means delaying a site that may already have been planned.

Review times

As an indication, the review of a prior declaration takes around one month, while a building permit takes several months. But two factors specific to Paris regularly extend these periods:

• the consultation of the architecte des Bâtiments de France, which adds extra review time whenever a historic monument is involved;
• any request for additional documents, which stops the clock until the completed file is received.

The pitfalls that cost the most

• Starting before approval. Undertaking works subject to authorisation without having obtained it exposes you to a site shutdown and reinstatement works.
• Confusing planning permission with co-ownership approval. A planning authorisation issued by the City never replaces the co-ownership’s approval where it is required: these are two separate tracks, to be pursued in parallel.
• Forgetting display and appeal periods. The authorisation must be displayed on site, after which a third-party appeal period begins. Starting major works too soon means taking an unnecessary legal risk.
• Neglecting completion. At the end of the works, a declaration certifies that the works comply with the authorisation. This document, often forgotten, is invaluable when the property is resold.
• Underestimating the application file. Inaccurate drawings, missing photographs, a poorly prepared contextual insertion: the leading cause of delay is not the administration, but an incomplete file.

A well-framed process, a calmer site

The Paris lesson is constant: the difficulty of a renovation is rarely resolved on site; it is prepared upstream. Identifying the right authorisation, anticipating the Bâtiments de France opinion, calibrating the 150 m² threshold, securing a change of destination, each of these steps, taken in time, avoids weeks of delay and costly rework.

This is precisely the framing work Lumiera integrates upstream of every Paris project: reading the property’s regulatory context, assembling a robust application and coordinating the procedures, so that authorisation is never the grain of sand that brings the site to a halt.

A project in Paris and unsure about the formalities? Let’s talk: together, we define the necessary authorisations before the first quotation.