Virtually all building works, involving either a new build or renovation, require the French equivalent of a building permit, or at least a notification of what work you intend to carry out. Applications are handled by your local Mairie, sometimes in conjunction with the regional office of the DDE who are responsible for overall town and country planning. In all cases it is advisable to consult them first, either in person or through an architect, as early discussions can give you an idea of what is or is not permissible, before commiting to any major expense.
Starting with the simplest, almost all interior work can be undertaken without any kind of planning permission, provided it does not alter the overall living area or affect the exterior of the building (such as creating new doors or windows). However, if you live in a co-ownership property, the rules of the 'syndic' (building management company) may affect what you can and cannot do, particularly if it affects load-bearing walls, the building's common parts, and exterior balconies or terraces. You will need to submit a request and plan to the annual general meeting of the co-owners for approval. The most common requests include joining two or more apartments to make a single unit, and glazing-in a balcony or loggia.
Exterior painting (known as 'ravalement') has to be carried out at regular intervals, according to local byelaws, and is subject to a prior declaration. There may be restrictions on colours and types of materials used. Permission must also be sought to erect scaffolding on a public path or highway, and to position a skip outside your home.
Works that are typically subject to a prior declaration include installing an open swimming pool, change of use that does not require major work, and small terraces not higher that 60 cms and/or less than 20 m²surface area. The declaration is lodged using a special form and the Mairie has one month to raise objections or propose modifications.
Closing-in your property with a wall or fence also requires prior declaration, and there may be limitations on height and the type of materials used, and restrictions or objections in relation to the public highway.
All other work will require a building permit, and the submission of a comprehensive dossier including plans, elevations and descriptions of the proposed construction. You are required to use an architect if the overall surface area is more than 170 m² - and frequently advisable in the case of smaller new builds or extensions.
The dossier is open for public inspection at the Mairie, where the planning department has a minimum of two months to reply (3 months if the archiect from 'batiments de France' has to be consulted, in the case of proposed works close to the site of a historic monument). Once issued, the building permit can be challenged by objectors (neighbours, conservation groups etc) during a further period of two months. As a result building works, even in straightforward cases, cannot start for a period of four or five months from initial submission.
Once construction starts, the Mairie must be notififed, and again on their completion, when a 'certificate of conformity' will be issued within 3 months, provided everyone is satisfied that the work has been completed in accordance with the original plan (subject to any alterations required).
It goes without saying that works that have been undertaken without the required permissions and approvals are subject to heavy sanctions and may in some cases be ordered to be pulled down.