Each of the levels in which a building is divided, whether above or below the level of the ground, provided that they are covered by a roof. The following are not included as floor space: roof space or attics, unless they are permanently inhabited or an economic activity is carried out there. Basements housing the installations of the building (boiler room, lift motor) are not considered either. Nor are those areas dedicated exclusively to garages serving as private parking for neighbours and not constituting the economic activity of a company.