Floor area figure — definition and alternatives in Switzerland
What is the floor area figure? - The definition
Die Floor area figure (GFZ) is the ratio of the sum of all floor areas (GF) to the eligible land area. It therefore describes how intensively a plot of land can be used: The higher the number, the more you can build. It is therefore a central factor that influences the structural density of a plot of land and its potential value.
In many cantons, the floor area figure is essential to control urban use and density, as it indicates exactly how much residential or commercial space may be built on a plot of land. Land with a higher GFZ is often more valuable because more usable space can be realized.
How do you calculate the floor area figure?
Die GFZ is used in accordance with IVHB (https://ivhb.ch/glossar/geschossflaechenziffer/) is determined by dividing the sum of the total floor areas by the eligible land area. Various area types are included in this floor area calculation:
- Main usable areas (HNF) — living spaces, offices and retail spaces.
- Auxiliary areas (NNF) — areas for warehouses, technical rooms.
- Traffic areas (VF) — Areas for stairwells, corridors and elevators.
- Construction surfaces (KF) — Areas required for walls, columns and other load-bearing components.
- functional surfaces (FF) — rooms for building services, e.g. boiler rooms.
The calculation formula is:
- floor area number = sum of all floor areas/ eligible land area
It is important that rooms with a clear height below the specified minimum dimensions are excluded from the calculation. The exact minimum amount regulations vary from canton to canton and must be obtained from the responsible building authority before the planning phase begins.
What is the eligible land area (AgSF)?
Die eligible land area (AgSF) comprises all areas of a plot of land that belong to the building zone and are relevant for development. According to Swiss SIA standard 421, house access roads and internal roads that open up the property are included in the calculation. On the other hand, areas that are part of the general development of the property, such as roads and roads for fine, rough and land development, are excluded. If the building plot is located in different building zones, the AgSF must be calculated individually for each zone.
What alternatives to the floor area figure are there?
Since construction law in Switzerland is regulated by canton, there is no uniform solution with regard to the floor area figure. Some cantons prefer other indicators to manage building density:
- Utilization rate (AZ): The utilization rate is an older calculation variable that is established in many cantons. It indicates the relationship between land area and floor area, but often only takes into account habitable areas and excludes usable areas such as cellars or balconies.
- kConstruction mass figure (BMZ): The building mass figure indicates the ratio between land area and aboveground building volume that may be realized. This indicator is becoming increasingly important in Switzerland.
Regional differences and developments
Not all cantons have included the floor area figure in their planning, and some still prefer the utilization rate. However, the IVHB allows cantons to choose between various indicators or to develop their own regulations that meet local requirements. By 2024, 18 cantons have committed themselves to IVHB and are thus using harmonised terms and measurement methods for development management, including indicators for distance and height measurements.
It is important for building owners, investors and developers to find out about the respective building law situation and the specific regulations on the floor area figure in the affected cantons, as these can have a direct impact on construction projects and the profitability of a project.
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