Located in the center of the old town, the 'Spalenhof' is one of Basel's most important buildings. Dating from the 13th century, it was converted into a merchant's home in the 15th and 16th centuries and was sold to the city in 1956. New apartments were planned as part of a program to upgrade the district as a residential area. In 1984, a preliminary investigation into the building's condition revealed that the Kaisersaal's roof structure at 12 x 12 meters was too huge by medieval standards, along with its massive, timber post-and-beam system and a painted cassette ceiling.
Two cabaret theaters had been created in the Kaisersaal in the 1970s: the Fauteuil in the basement, and the Tabourettli on the first floor. In the center of the building, the main timber beam had sunk, a problem that was compounded by the removal of three supports to create an unobstructed space in the Tabourettli's auditorium. Calatrava proposed suspending the ceiling, a load of 211 tons. The Kaisersaal's main beam was thereby relieved by the addition of a braced, triangulated structure embedded within the partition walls, distributing some of the load to the outside masonry. Support tension rods of brushed steel were suspended down through the building to carry the theater ceiling below, which now has an acoustic function.
Further support of the Tabourettli floor was required from below; and yet the foundations were almost non-existent. As an alternative to more drastic solutions that would have considerably altered the building's fabric, Calatrava introduced a steel trestle, strategically placed to divert the forces and further brace the sagging longitudinal beams of the first and second floors. This intervention saved the building. The trestle, onto which the loads of the building's first-floor beam are concentrated at a single point, supports two cantilevered structures: a translucent glass stair leading to the anteroom and cloak room on the first floor; and a glass bridge going across the double-height space to the theater.
The need for massive bearing members is thus avoided, and the new bracing forms a functional and modern counterpoint to the ancient framework. The acoustic ceiling of the theater is comprised of elongated, tapering panels of pear wood. The window shutters, which resemble winged lapels, fold upward. When closed, the shaped entrance door is designed to reveal a side entrance for late-comers. The bar, light fittings and furniture were also designed by Calatrava. His cloak room in the anteroom features an octagonal box that can be folded open for use — an exploration of a transformational, geometric object.
1986 - 1987