What is the difference between usable floor area (área útil), private gross floor area (área bruta privativa), gross floor area (área bruta), and dependent gross floor area (área dependente)?

In documentation, floor plans or real estate advertisements, you can see that a property has, for example, a usable floor area of 88 m2, a total private area of 120 m2, a total built-up area of 140 m2 and a utility room of 20 m2. What does all this mean? General rules for urban buildings (RGEU) contain definitions:

Gross internal area

The total area of the property, measured along the external perimeter of the outer walls and the axes of walls separating neighbouring units, and includes private balconies, ancillary rooms and a share of the common areas of the building. That is, it is the total area of the property, which includes garages, balconies, terraces, a storeroom, etc.

Usable floor area

The sum of the areas of all rooms, including porches, corridors, bathrooms, storerooms, and built-in wardrobes, measured along the internal perimeter of the walls enclosing the living space, with a deduction of up to 30 cm for internal walls, partitions, and ventilation ducts. In other words, this is the property area from which internal walls, partitions, and ventilation ducts are deducted, and consequently, this area is smaller than the built-up area.

Gross private area

Total area, measured along the external perimeter and wall axes, including enclosed private balconies, cellars and private attics belonging to this address. That is, it is the gross area excluding open balconies, the garage and the storeroom.

dependent area

Covered and enclosed areas for private use, even if they are part of common property, even if they are located outside the building, the use of which is ancillary to the use for which the building is intended. That is garages, store rooms or storage areas, animal quarters, accessible attics or cellars, and balconies. Basically, that which is not included in the general private area.

How do you calculate the area?

Now, let's return to the original example. We have an apartment with a floor area of 88 m2, a gross internal area of 120 m2, a gross building area of 140 m2 and 20 m2 of appurtenant area. All of this information can actually be correct, let's see: measuring the apartment by the internal perimeter of the walls, it has a usable area of 88 m2, however, taking into account internal walls, service ducts and partitions, the area becomes 120 m2, which corresponds to the gross private area. This apartment may have a balcony/garage/storage room, which correspond to 20 m2 of appurtenant area, and adding the gross private area gives the gross (construction) area.