Separation of basement and ground floor at the same level – what is included in the building coefficient

Basement A floor or part of a floor whose ceiling does not exceed a height of 1.20 meters.

The following are not included in the building coefficient:

For residential buildings, a basement floor with a surface area equal to that occupied by the building, intended for auxiliary uses, provided that its ceiling does not exceed 1.20 m from the final ground level at any point.
This floor may serve the main uses of the building provided that all or part of it constitutes a functional annex to an independent dwelling or dwellings and 50% of the area of the main use is included in the building coefficient. In this case, the requirements for natural lighting and ventilation do not apply.

In cases where, due to a steep slope, the ground floor and basement are separated (by a wall), the part of the basement that is connected to the main ground floor area that meets the ground floor requirements (ceiling height exceeding 1.20 m) is included in the building coefficient, because it is connected to the main area.

The part of it that is separated by a wall and whose roof does not exceed a height of 1.20 m is not included in the building coefficient.