PENZISBETTINI Extends Limmattal Cantonal School in Urdorf with Concrete Wings Built to Outlast Their Floor Plans

School extensions usually follow a simple formula: add classrooms, match the old brick or render, and keep the new building quiet. At Limmattal Cantonal School in Urdorf, PENZISBETTINI Architekten took a different route. The existing campus, built by Bolliger Hönger Dubach between 1984 and 1986, sits as a green island between small-scale housing to the south and an industrial and commercial belt to the north. Two pressures forced a rethink: the arrival of the Limmattalbahn tram line and a planned 50 percent increase in enrolment. The response is roughly 14,000 m² of new program, including an auditorium, a double gymnasium, science classrooms and a canteen, spread across new wings that turn a closed campus toward the street.

The program list is not what makes the project interesting. The structure is. The architects designed a concrete frame that sets where walls can connect, so rooms can be rearranged later without changing the character of the building. That is a sober, unglamorous idea, and it produced a building that earned the office a 2025 Betonpreis. We think it also offers a useful lesson about how public schools should be built when nobody can predict how teaching will change over the next fifty years.

Facing the Tram Instead of Hiding From It

The street corner tells you most of what you need to know. Large lettering spelling out AULA SPORT sits over wide steps, a few metres from the tram wires. This wing reads as civic infrastructure rather than as a private institution behind a fence. The auditorium and gyms are the parts of a school that a neighbourhood actually uses in the evening, and putting them at the public edge is a deliberate choice.

Above the ground floor, the facades settle into a disciplined rhythm of concrete piers, ribbed infill panels and tall glazing. The bays repeat without becoming monotonous because the depth of the piers creates shadow, and the glass reflects the surrounding buildings. On a five-storey block, that steady order does more to give the building presence than any formal gesture could.

Concrete With a Range of Surfaces

The architects use concrete as the main material, but not in a single finish. Rough surfaces with deep-set windows, pebbled aggregate faces with stepped projections and long smooth walls under corrugated metal bands sit beside each other across the campus. Each finish suits its job: heavier textures near the ground, where people touch and lean, and lighter cladding higher up.

The corrugated metal volumes matter more than they might seem. They acknowledge the industrial neighbours to the north instead of pretending the school sits in a park. The campus now takes its material cues from both sides of its site, and the extension feels like it belongs to Urdorf rather than to a catalogue of Swiss school buildings.

A Plaza Stitched Into the Old Campus

Working with S2L Landschaftsarchitekten of Zürich, the architects created a new plaza courtyard, the Platzhof, and linked it to the existing outdoor spaces with generous seating steps. The granite steps double as circulation and as a place to sit, which is the kind of overlap a school courtyard needs during breaks.

The planting is still young: bare trees with whitewashed trunks, mulch beds and timber benches set against grey concrete. The landscape will take a decade to catch up with the architecture. That is a realistic timeline for a public campus, and it is better than covering the site with instant greenery that will not survive.

The Spiral Stair as Centrepiece

The foyer of Trakt F centres on a spiral staircase made of passivated steel. It rises through a tall concrete hall next to a glazed wall with views back toward the town. Against raw concrete walls and a ceiling of oxidised metal panels, the brushed steel reads as the one polished object in a deliberately rough room.

It works because the room around it stays restrained. The stair does not need to compete with decorative finishes, and its curved balustrade frames the plainer details, such as wall lights and dark doorways, in a way that makes them feel considered. A school foyer gets used hard, and these materials will hold up to that use.

Prestressed Stairs and Steel Columns

A second stair takes a more technical approach. It is built from prefabricated concrete elements that are prestressed against each other, so the joints carry real structural load rather than simply being where the pieces happen to meet. Next to polished cylindrical columns and corrugated walls, the stair shows how it was assembled.

Seen through open glass doors, a galvanized steel stair sits under exposed ducts and concrete beams lit by fluorescent tubes. Nothing is hidden behind a suspended ceiling. Some readers will find that austere. We read it as honesty about how a building like this actually runs.

Trakt E: Laboratories With the Services Left in View

Trakt E holds the chemistry labs, music rooms and a central zone that can stay unfinished as an exhibition space or be fitted out as an open biology collection. A lit terrarium of bromeliads set into a corridor wall suggests the second option is already in use. Science teaching gains when the specimens leave the storeroom and sit along the corridors students walk every day.

The structure is visible here, with building services integrated into it during the shell construction. The labs keep their heavily serviced ceilings exposed, so ducts and pipes can be reached and changed without demolition. In the music rooms, the concrete walls are modulated to diffuse sound. That is a careful use of the material: the walls handle the acoustics without needing applied panels.

A Frame Built to Outlast Its Floor Plans

Trakt E uses prefabricated facade columns, and the construction photographs show them standing in a row beside a tower crane before the rest of the building went up. Prefabrication here is not just about speed. It keeps the structural grid fixed and precise, and that grid is what allows future change.

Because the load-bearing system defines where walls can connect, the interior partitions become replaceable. A classroom can become a lab, and a lab can become a seminar room, while the building keeps its identity. The timber auditorium, set inside the concrete as a room within a room, follows the same logic: it echoes the structure behind it but does not depend on it.

Plans and Drawings

The site plan shows the angled new wings and courtyard blocks fitted into an irregular plot alongside the original complex. The section through Trakt F shows two stacked ribbed halls with a central void for the spiral stair, and the floor plans place a tiered lecture hall next to an open foyer. The most revealing drawings are the exploded axonometrics. One separates services, prefabricated ribs and columns, and non-load-bearing walls into distinct layers. The other uses a Rubik's cube diagram to explain how the double gymnasium is rotated 90 degrees within the structural system.

Why This Project Matters

Swiss school design has a strong tradition of well-made concrete, so a good concrete school in the canton of Zürich is not news in itself. What sets Limmattal apart is that the structure carries the long-term planning. The building is designed around what will change inside it rather than around one fixed program, and that thinking shows from the prestressed stair to the exposed lab ceilings.

The project also handles growth well. A 50 percent increase in students could easily have produced a defensive block. Instead, PENZISBETTINI used the new tram line as a reason to face outward, put the shared spaces at the public edge and give the neighbourhood a plaza. For any town expanding an existing campus, this is a strong example of how to add capacity and become more public at the same time.

Limmattal Cantonal School by PENZISBETTINI Architekten, with landscape architecture by S2L Landschaftsarchitekten. Location: Urdorf, Switzerland. Area: 14,000 m². Year: 2024. Photography: Federico Farinatti.

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