What does the floor area ratio specifically mean?

The floor area ratio (AZ) is the ratio between the maximum permissible gross floor area (BGF) of a building and the chargeable plot area. An AZ of 0.6 on a 600 m² plot means that a total of 360 m² BGF — summed across all storeys — may be created. The AZ is the most important quantitative steering instrument of Swiss zoning planning alongside height, boundary setback and number of storeys.

Where do I find the AZ for a specific plot?

The AZ applicable to a specific plot is set out in the municipality's communal building and zoning regulations (BZR), in conjunction with the zoning plan. On the cantonal GIS portals (e.g. maps.zh.ch, geo.ag.ch, geo.gr.ch) the zone allocation is visible; you must look up the specific AZ per zone in the text of the regulations. The building authority provides information if the values are not unambiguous.

Is the attic counted towards the gross floor area?

This depends on the canton or municipality. Typically only those attic areas are counted whose clear height reaches a defined minimum (often 1.50 m, sometimes 2.00 m). Basements likewise only count towards the BGF if they are used for residential or commercial purposes — pure cellar rooms, technical rooms and underground car parks are generally not chargeable.

How much is a floor area reserve worth?

An unused reserve has a value that varies strongly depending on the location. Rule of thumb: 20 to 50 per cent of the average building land price per m² BGF — i.e. per m² of additional BGF that can be created. In urban locations with square-metre prices from CHF 5,000, even a 30 m² reserve produces a calculated added value in the six-figure range. The reserve is, however, only valuable if it can actually be realised under building law (boundary setbacks, height, number of storeys, monument protection).

Floor area ratio (Ausnützungsziffer, AZ): calculation, BMZ/GFZ distinction, reserve

Q: What is the difference between AZ, GFZ and BMZ?

The floor area ratio (AZ) measures the gross floor area in relation to the plot area and is a traditional Swiss term. The storey area ratio (GFZ) is the counterpart harmonised in the IVHB concordat — it counts, however, according to harmonised rules (chargeable storey area aGF). The building mass ratio (BMZ) does not measure the area but the above-ground building volume in m³ per m² of plot area and is therefore more relevant for industrial buildings and halls. AZ and GFZ are functionally related, BMZ is a different measurement dimension.

The floor area ratio (Ausnützungsziffer, AZ) is the ratio of gross floor area (Bruttogeschossfläche, BGF) to chargeable plot area and is therefore dimensionless. AZ 0.6 on a 600 m² plot allows a maximum of 360 m² BGF — summed across all storeys. It is the most important quantitative lever of Swiss land-use planning alongside height, number of storeys and boundary distance. The RPG (SR 700) makes no numerical requirements; the figure is set by cantons and municipalities in the building and zoning regulations (BZR). Typical residential-zone values lie between 0.3 and 2.5.

How do you calculate the floor area ratio?

AZ = gross floor area (BGF) ÷ chargeable plot area. Example: a 600 m² plot with AZ 0.6 yields a maximum of 360 m² BGF. Spread over the ground floor (120 m²), the 1st upper floor (120 m²) and an attic with a clear height over 1.50 m (100 m²), this gives 340 m² of chargeable BGF — just under the limit of 360 m². The basement (cellar, technical rooms) with 120 m² is not counted.

What is the difference between AZ, GFZ and BMZ?

The AZ measures BGF ÷ plot area (typically 0.3–2.5). The GFZ is the IVHB-harmonised counterpart using chargeable floor area (anrechenbare Geschossfläche, aGF), likewise 0.3–2.5. The BMZ, by contrast, measures the above-ground building volume in m³ per m² of plot (2–10 m³/m²) and is more relevant for industry and halls. The site coverage ratio (Überbauungsziffer, ÜZ, 0.2–0.5) limits the building footprint: ÜZ 0.3 on 600 m² allows a maximum of 180 m² of building footprint area.

Which areas count towards the gross floor area?

The BGF includes residential and commercial rooms of all above-ground storeys, heated winter gardens with residential use, converted attics with sufficient clear height, and circulation areas serving chargeable rooms. Not chargeable are pure cellar, technical, laundry and bicycle rooms, underground garages without residential use, open balconies and attic areas below the cantonal minimum. Customary for attic chargeability is a clear height from 1.50 m, in some cases 2.00 m.

How much is a floor-area-ratio reserve worth?

The reserve is the difference between the permissible and the actually built BGF. Example: an 800 m² plot with AZ 0.45 allows 360 m² BGF; with an existing 260 m² (ground floor + 1st upper floor, 130 m² each), 100 m² of reserve remain. Rule of thumb for the value: 20 to 50 percent of the average building-land price per m² of additionally buildable BGF. At per-square-metre prices from CHF 5'000, even 30 m² of reserve yields a calculated added value in the six-figure range — provided it is realisable under building law.

Where do the cantons differ on the AZ?

The IVHB (in force since 26 November 2010) harmonised 30 building terms — the AZ is deliberately not among them. Zurich, Aargau and Ticino continue to use the floor area ratio (ZH residential zones 0.4–1.0, centre 2.0–2.5; AG 0.3–0.7), Bern, Basel-Stadt and Graubünden use the GFZ. The canton of Zurich extended the IVHB implementation deadline from the original 28 February 2025 in early 2026 to 29 February 2028.

What does realising a reserve via up-zoning cost?

Since the RPG revision (in force since 1 May 2014, RPG Art. 5), up-zoning in almost all cantons is linked to an added-value levy of at least 20 percent, payable upon realisation or sale. With up-zoning-related reserves, 20 to 60 percent of the land's added value can flow to the canton or municipality — this sum belongs in the profitability calculation from the outset. Individual municipalities grant AZ bonuses of 5 to 10 percent for energy-efficient building or 10 to 20 percent for affordable housing.