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

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

Doesn't the notion of floor surface tell you anything? You don't know how it's calculated? Why do you have to measure the floor surface? We'll explain how.

The floor surface of the construction corresponds to sum of closed and covered surfaces, under a ceiling height greater than 1,80 m, calculated from the naked 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 surface is useful to know the city planning authorisation type due for your project building permit or prior declaration.

The footprint is also important for determining the type of city planning permission request.

Finally, the floor surface and ground right of way can reach the mandatory recourse to architect.

Warning

the floor area should not be confused with the private surface of the apartments Carrez. This defines the area of the private part of the lot or the fraction of the lot at the time of sale or the purchase of your property in condominium.

The floor surface is the sum of the surfaces of all built levels, closed and covered, including ceiling height is greater than 1,80 m, calculated from the inner nude (measured from the baseboards).

The floor surface is obtained after deduction of following surfaces :

Surfaces corresponding to the thickness of the walls surrounding the doors and windows facing the outside
Empties and hoppers (spaces under stairs and lifts)
Floor surfaces with a ceiling height of 1.80 m or less
Floor surfaces for the parking of motorised or non-motorised vehicles (including access ramps and manoeuvring areas)
Floor surfaces of non-convertible attic for housing or for activities of a professional, craft, industrial or commercial nature (e.g. attic with large frame footprint 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 for calculating the floor surface

FYI

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

The floor surface is obtained after deduction of following surfaces :

Surfaces corresponding to the thickness of the walls surrounding the doors and windows facing the outside
Empties and hoppers (spaces under stairs and lifts)
Floor surfaces with a ceiling height of 1.80 m or less
Floor surfaces for the parking of motorised or non-motorised vehicles (including access ramps and manoeuvring areas)
Floor surfaces of non-convertible attic for housing or for activities of a professional, craft, industrial or commercial nature (e.g. attic with a large frame footprint or a floor that cannot withstand loads)
Floor surfaces of technical premises 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 housing, provided that these premises are served only by a common part
Surface equal to 10% floor areas intended for housing, after deduction of the preceding points, provided that the accommodation is served by internal common 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 for calculating the floor surface

FYI

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

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