<Refurbishment and conversion of the Wallstrasse building ensemble, Basel, 2018–2025

Continuity and Transformation at the Bollwerk

Between the Elisabethenanlage, Basel’s main railway station and the historic city centre, the building ensemble occupies a point of intersection between different urban spaces and patterns of movement. For decades, the two former administrative buildings of the Basel Regional Telecommunications Directorate have given the site between Wallstrasse and Bollwerkpromenade, in the immediate vicinity of Basel SBB railway station, a precise and self-assured presence. The central location and direct access to public transport provide particular advantages for urban living.

The transformation of the ensemble, designed by Arnold Gfeller and his practice in the 1960s and 1970s, exemplifies the fundamental shift taking place in our culture of building. The functionalist administrative buildings are converted into new homes. The design does not begin by replacing the existing architecture with a new order, but by asking which spatial, structural and architectural possibilities are already inherent in the existing fabric.

The project therefore follows the principle of reusing existing land and building resources as comprehensively as possible. The massing, based on a development plan dating from 1950, accommodates a high density on land that is already built upon. The existing load-bearing structure, circulation systems and substantial parts of the interior fit-out within the basement levels are retained and incorporated into the transformed ensemble. The extensive technical infrastructure within the basement and plinth levels also remains operational. The new residential use is concentrated on the upper floors, allowing the ensemble to evolve within its established urban order.

The clear structural system provides a robust and adaptable basis for this transformation. The largely retained concrete frame, floor-to-floor heights of approximately three metres, deep floor plates and closely spaced façade columns allow for a new spatial organisation without the need for extensive intervention in the building fabric. The consistent reuse of the load-bearing structure reduces the material intervention while preserving the characteristic order of the existing architecture.

The Apartment as Loggia

The former office floors accommodate 105 compact apartments of varying sizes. Subtle shifts between the structural grid, the organisation of the rooms and the new façade allow for differentiated layouts. At the same time, they reveal the slender hexagonal façade columns, which become defining elements within the interiors.

Generously opening windows and low parapets extend the living spaces towards the building envelope. The low horizon of the parapet reinforces the vertical presence of the columns while opening broad views across the city. In the larger apartments, sliding doors connect the rooms along the façade. Interior, outlook and envelope are thus brought into a close spatial relationship: the apartment itself begins to resemble a loggia.

The compact apartments, most of which face in a single direction, are complemented by a series of shared amenities. Communal laundries with small adjoining living areas, a shared room opening onto the planted courtyard, garden courtyards and a communal roof terrace provide places for meeting and exchange. They extend private living into a collective realm while making use of the ensemble’s distinctive views and central location.

The Façade as Power Station

The architectural expression likewise evolves from the existing buildings. The horizontal façade bands and enclosed circulation cores remain defining elements of the ensemble, while the regular order of the former administrative buildings is given a new rhythm. Differing divisions of windows and parapets, recessed opening sections and fabric blinds overlay the structural grid with a layered, polyrhythmic composition.

The new façade makes the residential use perceptible without concealing the buildings’ origins. It translates the abstract order of the administrative architecture into a finer scale related to domestic life. The ensemble remains legible as a transformed office complex, and it is precisely this continuity that gives the project its distinct identity.

At the same time, the architectural language of post-war modernism provides ideal conditions for integrating photovoltaics into the building envelope. Rather than forming an additional technical layer, the solar modules are part of the architectural composition. Integrated into the parapet bands and the solid faces of the circulation cores, their textured surfaces respond to changing light and weather. The new façade not only improves the energy performance of the building envelope but also generates electricity.

Working with the existing fabric, introducing a new use, creating homes and embracing renewable energy shape the design. Rather than limiting its architectural possibilities, the consistent reuse and transformation of the existing structure form the basis for the project’s distinctive spatial and architectural qualities. The ensemble demonstrates how existing architecture can be developed through precise interventions and adapted to changing social and environmental requirements.