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

Verified 08 July 2022 - Directorate for Legal and Administrative Information (Prime Minister)

Does the notion of a floor surface mean anything to you? You don't know how it's calculated? Why do we need to measure the floor area? We will explain how to do this.

The floor area of the construction corresponds to sum of closed and covered areas, below a ceiling height more than 1,80 m, calculated from the interior of the building's facades. The floor area is calculated differently between the house and the collective building in the deductions to be made.

The floor area is used to determine the type ofcity planning authorization required for your project.

Beyond a certain floor area, it is necessary to to use the architect.

The footprint is also taken into account to determine the type of request. Depending on the destination of the buildings (agricultural, production greenhouses), the ground right-of-way is also decisive for the recourse to the architect.

Warning

the floor area must not be confused with the private area of the apartments in the Carrez law. The latter shall define the area of the private part of the lot or part of the lot on sale or the purchase of your property in joint ownership.

The floor area is the sum of the surfaces of all levels constructed. enclosed and covered, including the ceiling height is more than 1,80 m, calculated from the interior nude (measured from the skirting boards).

The floor area is obtained after deduction of the following areas :

Surfaces corresponding to the thickness of the walls surrounding the doorways of doors and windows to the outside
Voids and hoppers (spaces under stairs and elevators)
Floor surfaces with a ceiling height of 1,80 m or less
Floor surfaces fitted for the parking of motor vehicles and non-motor vehicles (including access ramps and maneuvering areas)
Floor surfaces of attic not suitable for housing or for professional, craft, industrial or commercial activities (for example, attic with large frame size or a floor that cannot withstand loads)

You must also deduct the thickness of insulating materials.

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

Method of calculating the floor area

FYI

In this form, reference is made to the taxable area, i.e. the area corresponding to the development tax.

The floor area is obtained after deduction of the following areas :

Surfaces corresponding to the thickness of the walls surrounding the doorways of doors and windows to the outside
Voids and hoppers (spaces under stairs and elevators)
Floor surfaces with a ceiling height of 1,80 m or less
Floor surfaces fitted for the parking of motor vehicles and non-motor vehicles (including access ramps and maneuvering areas)
Floor surfaces of attic not suitable for housing or for professional, craft, industrial or commercial activities (for example, attic with a large frame footprint or a floor that cannot withstand loads)
Floor surfaces of technical rooms necessary for the operation of a group of buildings or of a building other than a single house (including waste storage rooms)
Floor surfaces of cellars or cellars, attached to accommodation, provided that these spaces are served only by a common part
Area equal to 10% floor areas intended for housing, after deduction of the preceding points, provided that the housing is served by common internal areas

You must also deduct the thickness of insulating materials.

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

Method of calculating the floor area

FYI

In this form, reference is made to the taxable area, i.e. the area corresponding to the development tax.

Who can help me?

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