The useful surface is equal to the living area of the dwelling plus 50% of the surface area of the private annexes. Example: The annexes included in the calculation of the useful surface are the following: Cellars and basements, Attics and convertible attics, Sheds and workshops, Outdoor dryers and cellars, Balconies and loggias, Verandas, Accessible terraces on the floor or semi-buried. The HABITABLE...