The Kaifu Baths are the oldest swimming baths in Hamburg. As a result of structural deficiencies and the threat of the 115-year-old roof structure failing, the swimming hall was in dire need of modernization. New thermal saltwater baths were therefore created inside the historical outer walls. The saltwater pool is a jointless waterproof concrete construction integrated into the existing swimming pool. The monument preservation authorities insisted that the original shape of the arched roof be retained. Given the high ambient humidity and the six-percent salt content of the saltwater baths, a wooden structure using a veneered laminate was chosen. The main trusses span 14 metres with a thickness of mere 13 cm. The few supporting steel components were dimensioned such that they guarantee structural stability for many years even if the corrosion protection fails. The entire space under the roof is accessible for maintenance. All wooden sections were industrially prefabricated and rapidly assembled using a modular system. The supported LVL roof panel functions as a membrane to brace the swimming baths’ 27.5-metre-long exterior masonry walls.