In the new spa area of the Palais Thermal, a roof made by formTL consisting of a thin white membrane protects bathers from the elements and from prying eyes.
Radolfzell / Tübingen, October 2012. For 165 years, the old Graf-Eberhard Baths in Bad Wildbad, situated in the northern part of the Black Forest, have been considered one of Europe’s finest bathing temples. Built in 1847 directly over a thermal spring, the baths have undergone many different extensions and modernisations over the years. The ensemble is characterised by the new Eberhard baths, a terraced structure from the 70s, which has been empty for some years. These historic leisure baths with their ‘Maurische Halle’ (Moorish Room) and ‘Fürstenbädern’ (Prince’s Baths) are now extending their range of facilities with an outside canvas-covered spa area.
The town of Bad Wildbad lies in the idyllic and narrow Enztal valley in the northern part of the Black Forest. Due to this, it was decided to use the empty exterior area of the 70s structure for the extension. The renowned Stuttgart architecture firm Kauffmann Theilig & Partner created a friendly spa landscape, characterised by warm wood tones, on the second and third floors of the terrace structure. This landscape is enhanced by specially selected lighting. Bathers can access the new area via wooden stairs that lead up from the sauna’s inner courtyard in the historic baths. Here, they find themselves in a polygonal wooden landscape, with various sauna experiences on offer, before coming to the highlight of the area: a new outdoor rooftop pool that offers swimmers an impressive view of the valley.
In order to prevent people looking in from the nearby hotel and to offer sauna users privacy, the entire north-facing side of the pool level is covered by a filigree membrane construction. It also offers protection against the weather, as well as framing the view towards the south and east of the valley.
Despite the geometric and constructional challenges, or rather because of these, the light construction appears to float. As structural engineers, formTL (membrane specialists from Lake Constance), were responsible for the membrane roof project, from the drafting of the design to the supervision of its actual construction. Its basic structure consists of a pre-tensioned membrane with three high points and lateral anchoring. In order to offer effective protection from prying eyes, the membrane roof is tilted on its longest axis, forming some extreme geometrical shapes: the construction comprises some very steep and some very flat areas, the latter posing a particular challenge due to winter snow.
Moreover, the organically shaped high point rings around the masts are perfectly geometrically integrated into the double-curved membrane surface, offering unhindered views up to the sky. The unusual length of the freestanding front side is extraordinary. Even on open ground, this construction would have been a challenge. However, the fact that the construction was carried out on the already existing structure in Bad Wildbad increased its level of difficulty. Both the membrane protection and the outside pool by Kauffmann, Theilig & Partner had to be planned with as few interventions as possible into the existing construction. When placing the foot and anchoring points, added care had to be taken regarding the positions of the beams in the underlying levels. With its complexity and sophistication, this construction can compete with any of the challenging large-scale projects in the portfolio of membrane specialists formTL.