SBP
Gross floor area — surface brute de plancher (SBP), Bruttogeschossfläche (BGF), superficie utile lorda (SUL) — is the sum of a building's floor areas measured to the outer face of the walls, expressing its construction capacity. It is the numerator of the land utilisation index used across Switzerland.
The technical reference is standard SIA 416 "Areas and volumes of buildings", which sets a measurement method shared by architects and authorities. Gross floor area adds up the floor areas of every level, walls included, and differs from living area or net area: it measures capacity, not usable comfort.
What really matters, however, lies elsewhere: the municipal building regulations decide which areas count towards the index. Habitable basements, attics below a minimum height, covered balconies, technical rooms, stairwells and circulation may or may not be included depending on the municipality. The intercantonal agreement harmonising construction terminology (IVHB/AIHC) introduced common definitions, but it only applies where the canton or municipality has formally adopted it.
Gross floor area is the numerator of your building rights: permitted floor area = index × the parcel's reference area. A divergence over what counts can shift the result by several dozen square metres — a whole room, sometimes a whole storey.
It also determines whether a roof extension or an annexe stays within the permitted ceiling. Before drawing anything, two things must be known: the index applicable to the zone, and the definition of countable area used by the municipality. The second is far more often the source of error than the first.
Add the floor areas of each level measured to the outer face of the walls, then deduct the areas your municipal regulations expressly exclude. Where a basement, attic or circulation space is uncertain, the interpretation belongs to the municipal building department — have it confirmed before design work.
Gross floor area is measured to the outer face of the walls and covers every storey the regulations take into account; living area counts only the genuinely usable interior surfaces. Gross floor area is therefore always larger.
It depends on the municipality. Many regulations only count underground storeys if they are habitable or exceed a given height. The local definition prevails over any general rule.
SBP in French-speaking Switzerland, BGF in German-speaking cantons, SUL in Ticino. Their regulatory definitions do not overlap exactly from one canton to another.
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