In a PPE sale in Geneva, one figure carries authority in every discussion: the weighted surface area. It’s what allows an attic flat with a terrace to be compared to a ground floor flat with a garden, it’s what serious estimations are based on — and it’s the figure that listings distort the most. Here is how it is actually calculated, with a complete example, and the pitfalls to know before comparing two properties.
What is the weighted surface area?
The idea can be summed up in one sentence: not all square metres are equal. A square metre of living room does not have the same use value as a square metre of balcony, which does not have the same value as a square metre of cellar. The weighted surface area therefore adds up the surfaces of a unit by assigning each one a coefficient according to its use value: living space counts in full, annexes count as a fraction. The result provides an honest basis for comparison between properties with different configurations — it is the common language of condominium transactions in Geneva.
The usual weighting coefficients
Weighting is not a legal standard: it is a market practice, and the coefficients vary slightly depending on the expert and the actual quality of the surfaces. The orders of magnitude commonly accepted in Geneva are:
- Living surfaces (interior rooms, sufficient ceiling height): 100%;
- balconies and loggias: around 50%;
- terraces: roughly 30 to 50% depending on their use — a south-facing attic terrace is not weighted the same way as a shaded passageway;
- cellars and accessible annexes: around 25%;
- convertible attic space: 30 to 50% depending on comfort;
- private gardens: roughly 10%;
- walls: excluded — a common mistake is to include the walls within the living surface.
It is precisely because these coefficients are open to interpretation that a serious calculation requires a professional: two fifteen-square-metre terraces do not carry the same value depending on orientation, view and access.
The calculation, with a complete example
A flat with 100 m² of living space, with a 10 m² balcony, a 15 m² terrace, a 6 m² cellar and a 40 m² private garden:
- Living space: 100 m² × 100% = 100 m²
- Balcony: 10 m² × 50% = 5 m²
- Terrace: 15 m² × 30% = 4.5 m²
- Cellar: 6 m² × 25% = 1.5 m²
- Garden: 40 m² × 10% = 4 m²
Weighted surface area: 115 m² — whereas the raw total of the surfaces would give 171 m². The gap illustrates the whole issue: depending on which surface figure is used, the “price per square metre” of the same property changes by half. This is why comparing two listings without knowing which surface figure they display compares nothing at all.
Weighting is open to interpretation, measuring is not: the SIA 416 standard
Two operations that are constantly confused need to be distinguished. Weighting — deciding that a balcony is worth half a living room — is a market practice, debatable and debated. Measuring — stating that this balcony is ten square metres — is not: Switzerland has its own standard, SIA 416, published by the Swiss Society of Engineers and Architects, in force in its 2003 edition.
It distinguishes thirty-one types of surfaces — floor surface, useful surface, secondary surface, clearance surface, technical surfaces… — and sets out how each one is measured: horizontal surfaces according to their actual dimensions, sloped surfaces according to their vertical projection. This standard underpins PPE plans, new-build construction and statistical estimation models.
The direct consequence for a buyer: when a listing states “120 m²”, the useful question is not “is that a lot?” but “which of the thirty-one?”. Ask for the PPE plan: it carries surfaces measured according to the standard, and that is where a weighting calculation must start from. A figure that is not linked to any named surface is not a measurement, it is an assertion.
The PPE plan states the origin, not necessarily the current state
A nuance we regularly encounter on the ground: the PPE plan describes the unit as it was originally constituted. A loggia closed in ten years later, an attic converted, a partition moved — the lived reality of the property drifts away from the document without the document itself changing. The discrepancy is not fraud: it is simply the life of a flat.
It is dealt with by naming it. Before selling, an on-site contradictory survey, checked against the plan, avoids the unpleasant discussion on the last day — the one where the buyer discovers that the square metres advertised are not those on the register, and reopens negotiations a fortnight before signing.
From calculation to price: the right and the wrong method
The weighted surface area becomes a price when it is multiplied by a price per square metre — and that is where everything is decided. The wrong method: taking an average of listings, which mixes heterogeneous surfaces and prices that were never signed off. The right one: starting from the actually registered transactions for the commune, or even the very same street, then adjusting for what the figures do not say — condition, floor, view, age, building amenities. This is exactly the work involved in a professional estimation; the weighted surface area is its foundation, never its outcome.
Weighted, living, useful, PPE: which one is authoritative?
The weighted surface area is just one of the surface figures circulating in a sale file: the living surface excludes walls and annexes, the useful surface adds accessible spaces, the gross surface includes the walls, and the PPE sheet from the land registry defines the unit’s ownership shares. Each has its own use and exclusions — our guide to surface types covers them all. The habit to keep: whenever you see a surface figure, ask which one — and on what basis it was measured.
What to remember
The weighted surface area is the benchmark for PPE transactions in Geneva: it counts living space in full and annexes as a fraction, according to use-based coefficients that are open to interpretation. It makes properties comparable — provided it is calculated rigorously and converted into a price using registered sales, not listings. To get a sense of where your property stands, explore the properties for sale on the Left Bank and the terms in the glossary; for a figure you can rely on, an estimation does the complete work, weighted surface area included.