Start at the rails. At the junction of Kalkbreitestrasse and Badenerstrasse in Zürich Kreis 4, VBZ trams still roll into a working depot every night. Above them sits a small city. Kalkbreite is one tiered, polygonal perimeter block wrapped around and over that depot, with a single public route climbing through it. Müller Sigrist Architekten won the 2009 competition and built it between 2012 and 2014 for CHF 75 million. The client was Genossenschaft Kalkbreite, a cooperative founded in 2007. It worked with the City of Zürich, which owns the land and grants it under a Baurecht.

Pascal Müller put the intent plainly to Metropolis: “We did not want to make a division between the tram and the building, or commerce and living.” Read the project as a vertical section.

The section, layer by layer

• Rails: the VBZ depot, still operating. The tram stop is folded into a café and plaza set back from the street.
• City ring: about 20 commercial and cultural spaces, roughly 5,000 m² in total, including the Kino Houdini cinema, restaurants, shops, offices and a guesthouse. About 200 people work there.
• Depot roof: a public courtyard about three storeys above the street, open to the neighbourhood, plus roof gardens for residents.
• Housing: 88 flats of up to 9.5 rooms plus 9 short-let “joker rooms”, for about 256 residents. The types include family flats, cluster apartments and a Grosshaushalt of about 50 people who share a professional kitchen, each keeping a small private flat.
• Connector: the rue intérieure, an internal street that links the cafeteria, workshop, music room, sauna and every level into one walkable loop.

Credit belongs to more than the architects. Neighbourhood advocates asked for housing on this depot from the 1970s onward, and the city opened the site to proposals in 2007. VBZ agreed to keep a live yard under 256 people’s floors, and its depot crews still work beneath the courtyard every shift. The block exists because all of them kept going.

The rule set is the architecture

The geometry holds the uses together, and so do a few written rules. German Wikipedia, citing cooperative data, records that residents average 31.2 m² each, against a Zürich average of about 39 m². There must be at least one person per bedroom. Residents sign a declaration that they will not own a car, because the tram is at their feet. Rent is set on cost, with construction amortised over 60 years, not on the market. Metropolis reported about CHF 2,000 a month for a 100 m² flat. The building is Minergie-P-Eco, and since January 2017 it has been one of only five Swiss sites certified as a 2000-Watt-Areal in Betrieb. That target works out to about 48 kWh of primary energy per person per day, and Zürich wrote it into its constitution after a 2008 vote.

The rules carry a real trade-off. The occupancy rule and the car-free pledge keep the block dense and cheap, but a household that shrinks or changes has to move within the building or leave. The flexibility sits in the rules and the joker rooms, not in the individual flat. PAZ has touched this thread before. Our piece on 24 affordable units in Igualada named Kalkbreite as the precedent for treating shared space as a productive factor, and noted that governance, not floor plan, decides whether that holds.

←TODAY: In 2026, Zürich still runs trams under 256 residents, and the depot roof is a public square. →3012: Every yard, depot and station roof in the city is read as a foundation for housing that is still waiting to be built. Fulcrum: Infrastructure lasts for centuries while housing turns over every generation, so a stack only works when the rules let the upper layers change without touching the rails.

What to take from the section

Stacking a programme over infrastructure is mostly an interface problem. You need three things. The first is a transfer level that respects the depot’s grid and clearances. The second is a public layer that absorbs the noise and the edge. The third is a circulation spine that keeps the upper floors from sealing into a podium. Kalkbreite puts the transfer at the courtyard and the spine in the rue intérieure. Offices that treat the rules as design inputs from the first sketch reach a buildable section faster.

Atelier: When a canton or a transport operator puts a depot, yard or station roof into a Wettbewerb, the winning office will be the one that presents the section and the rule set side by side. The Monday move: draft a one-page “rules sheet” template covering m² per person, parking stance, rent basis and energy target, and require it next to every section study in your next competition.

Hack: Stack the Kalkbreite section as named, parameterised layers above a footprint, so that a changed depot clearance lifts every floor above it. In a Grasshopper Python component, feed in a footprint rectangle and a list of “name:height” strings. The heights below are placeholders, not measured values.

import Rhino.Geometry as rg
z, bands = 0.0, []
for name, h in (s.split(":") for s in stack):  # e.g. "depot:7", "city:9", "court:0.5", "housing:18"
    bands.append(rg.Box(base.Plane, base.X, base.Y, rg.Interval(z, z + float(h)))); z += float(h)
a = bands

Pass each band to Archicad as its own story or zone through the PAZ Grasshopper↔Archicad Library. PAZ BSS graduate Monika Lenczuk used the same Rhino-to-BIM path for her Honeycomb City. If you change the depot band, the whole section re-seats.

From where I sit, the cities that came through well had no spare land and kept their yards anyway, by building over them. Before your next site visit, walk the nearest depot and sketch its section from the rails up.