Every Swiss plot carries a maximum that anyone can compute: plot area times Ausnützungsziffer. Two numbers and one multiplication give the floor area a Gemeinde will let you build. The arithmetic is public. The second number is where it gets interesting, because the AZ belongs to the cantons.

The IVHB, the intercantonal agreement on harmonised building terms, was adopted on 22 September 2005 by the Bau-, Planungs- und Umweltdirektoren-Konferenz and covers 30 building-law terms and measuring methods, as the Stadt Luzern Stadtplanung summary by Michèle Kühnis (version 10.10.2021) records. It harmonised four density figures: Geschossflächenziffer, Baumassenziffer, Überbauungsziffer and Grünflächenziffer. As the Kanton Luzern Erläuterungen to its Planungsvorschriften put it, the agreement deliberately does not provide for the Ausnützungsziffer, which the cantons regulate “unterschiedlichst”. Luzern now states the Überbauungsziffer in place of the AZ, while other cantons and Gemeinden keep it. The planners and conference members behind those 30 terms spent years agreeing what a word measures. Their quiet work is why a figure on a zoning plan means anything at all.

That patchwork is why a Swiss feasibility study is a GIS problem before it is a design problem. Before a single volume is drawn, someone has to know the parcel, its zone and the figure that zone allows. That data lives in public geodata, kept current by surveying offices whose names rarely reach a project credit list.

The chain we teach

Our online course “Maximale Ausnützung: Grundstücksoptimierung von GIS bis zu BIM” sits on the workshops page with the status “Warteliste! Start in 2026!”. It reads as one chain in six sections. It opens by loading GIS data from any source into usable 3D ground, then moves from manual steps to automated workflows. The third section is the heart: “Von Unsicherheit zu Klarheit über das maximale AZ”, where building-law and volume calculations run across several Bebauungsvarianten at once. Optimisation follows, then BIM objects that respond to changes, then visualisations a client can read.

The FAQ is plain. Rhino, Grasshopper and freely available GIS data; no GIS or BIM prerequisites; 3–5 hours a week, designed to sit beside a full-time job; years of access; a 14-day guarantee; a certificate on completion. The course description says the path runs 8 weeks, built around one practice project. The waitlist lives on our workshops page.

←TODAY: In 2026 the AZ still differs canton by canton, 21 years after the IVHB left it out.
→3012: Zurich-3012 reads every plot’s maximum from the ground it stands on; the argument starts at the variants.
Fulcrum: Because the ratio is public arithmetic, the hours it frees belong to design.

The lineage is our own. Since 2010 the house has built Rhino and Grasshopper add-ons, and the Grasshopper Volumenstudie add-on takes exactly the inputs this course teaches you to reason with: “AZ, Gebäudehöhe, maximale Ausnützung”. Grasshopper itself, David Rutten’s work at McNeel, is what lets a ratio drive geometry in the first place. At the BIM end, the separate Archicad Volumenstudie add-on asks for plot area, AZ and building height and builds envelope, slabs, walls and zone stamps with their floor areas: Archicad automation at the moment a variant becomes a model.

Why it matters on the desk: PAZ’s own Machbarkeitsstudie-Zeitrechner estimates the manual route at “15-25 Stunden pro Machbarkeitsstudie”, spent re-typing GIS data, remodelling each variant and re-checking ratios. Read that as our estimate; it has never been a measured study. The trade-off is real too: an automated chain is only as current as the zone figure you feed it, and a wrong AZ produces wrong variants faster.

Yesterday’s piece, The 1.15 City, followed the same ratio up to city scale.

Atelier: For a small Zürich studio testing AI-assisted variant tools, the risk sits in the input: an optimiser will chase whatever maximum you hand it, so the AZ has to be sourced and checkable. On Monday, set one office rule: every variant sheet references a single cell for permitted floor area, with the Bau- und Zonenordnung citation written beside it, and nobody retypes it.

Hack: Pin the plot’s maximum before any volume exists, then see what it means per floor. Drop this into a GhPython component in Grasshopper, or run it as plain Python; the values are placeholders for your own plot.

plot_area = 1000.0   # m², placeholder: from your cadastral plan
az = 0.8             # placeholder: AZ from your Bau- und Zonenordnung
max_gf = plot_area * az
for floors in (3, 4, 5):
    print(floors, "floors ->", round(max_gf / floors), "m² per floor")

Three floors means a fat footprint; five means a slim one, if the Gebäudehöhe allows five. The building height caps the loop, and that cap is your next input.

Write your plot’s three numbers on one line before you open Rhino.