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Floor area of a construction: what are the calculation rules?

Verified 15 avril 2020 - Directorate for Legal and Administrative Information (Prime Minister)

The floor area is based on specific criteria, depending on whether it is a house or a collective building. The floor area allows to know the planning authorization required for its construction or construction project. The right-of-way on the ground is also decisive.

  Warning : the floor surface should not be confused with the private surface of the apartments of the Carrez law. This defines the area of the private part of the lot or the fraction of the lot when selling or buying a property in a condominium.

House

The floor area is the sum of the surfaces of all levels constructed, closed and covered, with a ceiling height greater than 1,80 m.

It can be measured inside the walls of the façades of the building: it does not take into account the thickness of the external walls, whether or not they are carriers, and whatever the material they are made of (brick, glass, stone, etc.). The thickness of insulation materials shall also be deducted.

The floor surface is obtained after deduction of the following surfaces:

  • Surfaces corresponding to the thickness of the walls surrounding the embers of the doors and windows overlooking the outside
  • Empty and hopper (corresponding to stairs and elevators)
  • Floor surfaces with a ceiling height of 1,80 m or less
  • Floor surfaces for the parking of motorized and non-motorized vehicles, including access ramps and maneuvering areas
  • Floor surfaces of attic not suitable for housing or for activities of a professional, craft, industrial or commercial nature (e.g. attic with a large structural footprint or a floor that cannot support loads)

To help you calculate the floor area of your construction, you can help you with a calculation method.

Collective building

The floor area is the sum of the surfaces of all levels constructed, closed and covered, with a ceiling height greater than 1,80 m.

It can be measured inside the walls of the façades of the building: it does not take into account the thickness of the external walls, whether or not they are carriers, and whatever the material they are made of (brick, glass, stone, etc.). The thickness of insulation materials shall also be deducted.

The floor surface is obtained after deduction of the following surfaces:

  • Surfaces corresponding to the thickness of the walls surrounding the embers of the doors and windows overlooking the outside
  • Empty and hopper (corresponding to stairs and elevators)
  • Floor surfaces with a ceiling height of 1,80 m or less
  • Floor surfaces for the parking of motorized and non-motorized vehicles, including access ramps and maneuvering areas
  • Floor surfaces of attic not suitable for housing or for activities of a professional, craft, industrial or commercial nature (e.g. attic with a large structural footprint or a floor that cannot support loads)
  • Floor surfaces of technical premises necessary for the operation of a group of buildings or of a building other than a single-family home, including waste storage rooms
  • Floor surfaces of cellars or cellars, attached to dwellings, provided that these premises are served only by a common part
  • Area equal to 10 % of the floor areas intended for housing, after deduction of the preceding points, provided that the accommodation is served by common interior areas

  Warning : in condominiums, in certain situations, an authorization by the general assembly of the co-owners is required prior to any work. This is particularly the case when working on a common part on private use (e.g. creation of a veranda on a common terrace).

To help you calculate the floor area of your building, you can use a calculation method.