The supporting structure of the extension is executed as a massive construction with a roof that has a lightweight steel and wood design and a wooden façade. The existing wooden roof construction over the main swimming pool had serious corrosion damage around the steel connecting elements and no longer met the structural safety requirements. The existing trussed girders were replaced by trussed glulam girders arranged in the grid of the existing trussed girders and resting on the existing support columns. The design of the girders was selected such that they could be installed from the interior, without taking off the roof, be-cause the roof cladding was still in good condition.