Gross floor area — meaning and calculation
What is the gross floor area (GFA)? The definition
The gross floor area is defined as all surface and underground floor areas of a building. It is important to note that, despite widespread use, the term gross floor area not defined as binding IS.In Switzerland is the SIA https://www.sia.ch/de (Swiss Engineering and Architecture Association) responsible for defining key figures and standards. The term gross floor area is not included in the relevant SIA 416 standard. The closest is the term floor area (GF), which is defined as “the floor plan area of the accessible floors, including the construction areas, which is enclosed and covered on all sides.”
The SIA defines the following compulsory area names:
GF Graph floor areaDetermination of the realizable floor area (GF) with the utilization figure (AZ)
The utilization rate is used by cantons and municipalities to determine the permitted development of a plot of land and is expressed as a percentage. It is determined by multiplying the eligible land area by the utilization figure. The eligible land area comprises the plot of land to be developed, minus green and free zones, bodies of water and forest areas, as well as access roads and sidewalks as well as traffic facilities for which the required permit process has already been initiated. The utilization rate can be found in the building and zoning regulations (BZO) of your municipality.
Example: You have a plot of land with an eligible land area of 1,000 m2 and a utilization rate of 80%. The realizable, above-ground floor area is therefore 800m2.
Determination of the realizable main usable area (HNF)
In order to calculate the main usable area from the floor area, all construction areas (walls), traffic areas (stairwells and corridors outside the apartments), functional areas (e.g. building services rooms) and ancillary areas (e.g. laundry rooms) must be deducted. As a rule of thumb, it can be assumed that the ratio of floor area to main usable area is approximately 0.75.
Example: You now know that you are allowed to build a floor area of 800m2. Multiply the GF by 0.75, the result is a main usable area of 600m2. This allows you to create approximately 600m2 of living space or gross living space.
Read our article about living spaces HERE.
What is the difference between gross living area and gross floor area?
There is a risk of confusing similar terms when looking at the key figures of a property.
- The gross living area includes all usable interior areas of a building, including the outer wall cross-sections.
- However, the gross floor area also includes external stairwells, balconies, terraces and workshops.
From gross floor area to energy index
The energy index is used to easily and quickly assess a building's capacity as an energy consumer. It is regulated in SIA standard 180/4. This key figure shows the energy consumption of a building and makes it possible to compare different objects. For calculation, the gross floor area is divided by the energy requirement of the property (e.g. heating oil, gas, electricity or water consumption).
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