Total renovation and conversion of a 1960s concrete service building
The public swimming pool Gartenbad Bachgraben was built in 1962 after plans by Otto and Walter Senn in collaboration with the engineer Heinz Hossdorf. The concrete buildings distributed across the site are exemplary of post-war modernism and are listed in the inventory of the Basel-Stadt monument preservation authorities. The service building directly next to the main entrance to the pool grounds had only been partially renovated since its construction and was in need of a complete refurbishment. The staff areas no longer met the current use requirements and the restaurant had not been in operation since 2011 due to various issues.
The brief called for the integration of three different uses: a self-service restaurant, operation rooms for the pool staff and a youth centre with year-round operation, but without access to the pool grounds. MET Architects won the planner selection process and, after a careful analysis of the existing building, convinced the client to relocate the youth centre to the former caretaker's building, which was much better suited for this purpose. This enabled the restaurant building to be refurbished in a respectful and substance-preserving manner, subordinating the programme requirements and technical demands to the listed building.
In line with the maxims of the 1960s, the load-bearing structure of the building was designed in a functional manner with minimalist dimensions. The new uses were integrated according to the spatial possibilities. The upper floor, which previously accommodated a large production kitchen with a kiosk-like window for customer service, was converted into a self-service area accessible to all guests, which opens onto a partially covered terrace with a view of the outdoor area of the pool. The new restaurant kitchen with ancillary rooms extends along the north-west façade facing the street. Where structural alterations were necessary, they were implemented as faithfully as possible to the builders' intentions. The new concrete beams, for example, are barely distinguishable from the existing ones thanks to the carefully planned formwork.
A lift and an additional staircase were installed for disabled access, transport of goods and easier access to the upper floor. On the ground floor, public toilets, changing and break rooms for staff, a first-aid room, a multifunctional room and a garage for maintaining the grounds of the garden pool were added. New openings on the garden facing side of the ground floor were carefully integrated into the façade and reveal the use of the space behind them, while the new folding garage door on the side of the building blends seamlessly into the existing structure.
The exposed concrete façade was in very poor condition before the renovation. The reinforcement, which had corroded over the years, had been improperly repaired and the façade surfaces had been plastered and painted over several times. Instead of a CO2- intensive reconstruction, a detailed ‘repair concept’ was developed in collaboration with the conservation authorities. After removal of the surface layers and restoration of the reinforcement, the concrete was waterproofed and the colour and graphic formwork structure of the historical surfaces restored by means of retouching.
The energetic optimisation was also planned with a focus on preserving the building's fabric. The existing interior insulation was replaced in the same thickness, new double glazing was installed in the existing wooden window frames and motorised solar shading was added to minimise undesired heat gains. A heat pump with geothermal probes and a flat photovoltaic system on the green roof, invisible from the outside, supply most of the electricity required by the cold storage rooms and appliances. These targeted measures have enabled the listed exposed concrete building to be adapted to current sustainability goals and energy standards.
The interior of the building, which was originally not open to the public, was designed in a functional and monochromatic style. To accommodate the restaurant with up to 7,000 guests at weekends, the interior surfaces were completely overhauled. A floor pattern in the anteroom from the time of construction served as inspiration for the layout of the tiled floor with friendly swimming pool colours. Walls, built-in furniture and panels in a confident royal shade of blue create a unified spatial coherence in the rooms accessible to the public, while the operating rooms are designed in subdued tones in keeping with the historical logic.
Construction management: Martini Schäfer Baumanagement GmbH, Basel
Structural engineering: wh-p Ingenieure AG, Basel
Electrical engineering: Eplan AG Elektroengineering, Reinach
Mechanical engineering: Herrmann + Partner Energietechnik GmbH, Basel
Sanitary engineering: Bogenschütz AG, Basel
Photographer: Barbara Bühler
