A historic 1960s swimming complex in Allschwil, Switzerland, has reopened after an innovative restoration that preserves its mid-century modern heritage while meeting contemporary needs. The Gartenbad am Bachgraben, originally built in 1962 by renowned architect brothers Otto and Walter Senn in collaboration with engineer Heinz Hossdorf, underwent a comprehensive renovation of its restaurant and service building by Basel-based MET Architects.
The swimming facility, now protected as a heritage site, represents a prime example of post-war recreational architecture. The complex features several low concrete buildings arranged around pools set into expansive lawn areas near the Basel-Allschwil border. While the entire ensemble bears the distinctive design signature of the Senn brothers, each building was crafted to reflect its specific function, creating a harmonious yet varied architectural landscape.
Otto Heinrich Senn, the better-known of the two brothers, gained recognition for notable works including the Parkhaus Zossen apartment complex in Basel (1938) and his residential contribution to Berlin's Interbau exhibition in 1957. Walter Senn joined his brother's firm in 1933, typically handling construction execution while Otto Heinrich focused on design and public representation. Their collaborative approach proved particularly effective for the Gartenbad project, where functional diversity demanded both creative vision and technical expertise.
The restaurant and service building, located in the northwest corner of the sprawling complex, had been closed since 2011 and required urgent attention. The flat, cubic structure presents a stern, closed facade to the street while opening generously toward the pool area with deep terraces on both levels. The Basel-Stadt Building and Transportation Department initially envisioned three uses for the renovated space: a self-service restaurant, operational facilities, and a separate youth center.
MET Architects, specialists in post-war building restoration, won the open competition with their sensitive approach to heritage preservation. They successfully convinced the client to relocate the youth center to the complex's former gatehouse, preventing overcrowding in the main building. Having completed the gatehouse renovation in 2021, MET applied lessons learned from that project to the larger restaurant building, which encompasses nearly 900 square meters of floor space.
The architects faced significant challenges with the deteriorating concrete facades, which had suffered from corroded reinforcement and multiple layers of inappropriate repairs, plaster, and paint over the decades. Rather than reconstructing the surfaces with new concrete layers, MET developed an innovative 'patch concept' in collaboration with heritage preservation officials. This approach involved carefully removing accumulated surface layers before applying deep hydrophobic treatment to protect near-surface pores against moisture penetration.
The restoration team then executed targeted retouching to recreate the color and texture of the original board-marked concrete surfaces. This meticulous process preserved the building's authentic mid-century character while ensuring long-term structural integrity. The technique represents a breakthrough in heritage concrete restoration, balancing preservation principles with practical durability requirements.
Inside the renovated building, the upper floor now houses the self-service restaurant, while the ground level accommodates restrooms, staff changing areas, a medical room, a multipurpose space, and a garage. New additions include an elevator and staircase, designed to blend seamlessly with existing elements. The architects matched the formwork patterns of additional concrete beams to maintain visual consistency throughout the structure.
MET replaced the original interior insulation with materials of identical thickness, installed new glazing within existing wooden frames, and added motorized sun protection systems. The building's energy needs are largely met by a heat pump system and a low-angle photovoltaic installation on the roof, demonstrating how heritage buildings can achieve modern sustainability standards without compromising their historic character.
The interior surfaces received careful color treatment, with designers drawing inspiration from an original laying pattern found in an anteroom for the new flooring design. This attention to historical detail ensures that up to 7,000 weekend visitors can enjoy an authentic 1960s atmosphere in the Senn brothers' architectural creation. The project's construction costs totaled approximately 5.5 million euros, representing a significant investment in preserving Switzerland's post-war architectural heritage while adapting it for contemporary use.
