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Since April 2014 and the Duflot Alur law, the building surface, which must be differentiated from the floor area, is no longer calculated according to the same rules and the same criteria. The calculation is now more complex and it is recommended to use a professional sector to avoid miscalculation.

The building surface

The building surface

Difference between building surface and floor area

The building surface is the surface of a land on which it is authorized to build. It defines the value of your land.
The floor area is the area of ​​all levels constructed, enclosed and open with a height greater than 1.80 m. It is taken into account to define the obligation or not to have recourse to an architect for the establishment of the building permit. Please note that if the floor area is more than 170 m², you must call in an architect. The floor area replaces the Net Surface Area (SHON) and no longer takes into account the thickness of the walls in order to encourage individuals to better isolate their home.

Buildable surface: what has changed

Before April 2014, the building area depended on the Land Use Coefficient (COS) set by the Local Urban Plan (PLU). However, things have changed since the end of March 2014. The COS disappeared in the communes with a Local Town Planning Plan and will have disappeared completely within 3 years in the other communes. Before, it was enough to multiply the surface of the ground by the Coefficient of Occupation on the Ground to know the building surface. The calculation was simple and accessible to everyone. Given that the COS is gone, it exists today another method to calculate the building surface that takes into account other factors.

How to calculate the building surface

If the calculation for to know the building surface a field was simple in the past, it is more complex today.
Know, first of all, that to calculate the buildable area, you will have to look in the Local Urban Plan (PLU) many data, starting with the general rules of construction of your municipality. You will also need to know the area U of your parcel and the rules specific to your area such as the number of levels allowed.
You will need to inquire about the maximum height at the ridge and on the Ground Factor (CES). This coefficient defines the maximum of footprint that your construction can occupy on your land. It is after having gathered all this information that you will be able to evaluate the building surface. To avoid mistakes, it is more than recommended to call a professional.