Wohlen High School, Roofs and Hall

Calatrava approached the commission as a spatial definition of each respective building component. Four separate interventions are treated as independent events within the complex as a whole. For each space, Calatrava used a dramatically different system of construction, choosing one dominant material which was then exploited and investigated according to inherent physical and aesthetic qualities. These qualities were reflected and heightened in turn by the high standard of craftsmanship achieved. The Entrance: The courtyard is defined by the southwest ends of two converging blocks, which form the geometric basis of the complex. The entrance canopy fills the narrowing space between these blocks and is supported by a steel, tubular arch that in plan runs obliquely to the surface of the glazed facade. Spanning 20 meters, this arched spine is the point of attachment for a series of tapering profiles that make up the ribs supporting the two glazed, dihedral surfaces that form the sections of two intersecting cones. In plan, the outer edges of these surfaces are parallel, with the arch running diagonally across their combined rhomboid shape. The structure is steadied against the mullions of the facade, which are extended as required to match the sweeping rhythm of the canopy.

This steel construction, with its materials and rhythm, forms a unit with the entrance facade and is thus continuous with it from both the aesthetic and structural point of view. The Lobby: A circular opening in the roof brings a unifying focus to an otherwise irregular entrance hall. A series of radial, repeating timber units fills the annular roof space and rests on a steel tension ring at its edge. Each petal-like segment is elegantly cut away, and loads are carried to the central compression ring through laminated and turned pine spindles set in steel sleeves. The units are 5.4 meters in length on their lower sides, and the pattern is repeated 20 times to create a petal-like design over an opening of 11.36 meters diameter. The diameter of the glazed roof lantern is two meters. The Library: For the library, which is located off the lobby, the roof explores the structural properties of a concrete shell. Four thin, reinforced planes meet to create a compound form that imitates an open book.

A single, strengthened, steel column four meters high is located at the intersection of the four vaults that make up the space, and takes the entire weight of this roof. At the same time, it serves as the down-pipe for rainwater. The shell, which does not extend to the walls, accentuates the relationship between its flowing surface and the column, while allowing daylight to filter into the space below. The roof, cast in-situ, is stabilized using small-scale, discretely placed steel spindles. The Assembly Hall: The concrete columns of the assembly hall are cast in two bonded halves and are designed to directly absorb the loads transmitted by the roof structure. Facing each other as a mirror image across the 'vault' of the auditorium, the columns add a sphinx-like dignity to this lofty space, with its central access aisles to both sides. The assembly hall also functions as a large music room with modern electronics studio. At 16 by 28 meters, it is roofed by five precisely prefabricated three-pin parabolic arches of eight meters span. Such was the accuracy of fabrication that the arches were erected in a single day.

The arches are of a deep triangulated section. Individual rough cut, untreated pine battens — organized in a radial pattern fanning upward from a theoretical mid-point below the floor surface — form the braces between the laminated lower member and the shallower parabola of the upper members. The upper members are joined by acoustically treated horizontal board. The arches bear the full weight of the barrel roof, thus relieving the walls and enabling the non-supporting skylight to run the full length of the roof's edge.

As with the library and lobby, the choice of materials and artificial treatment of light in the assembly hall encapsulates the basic design approach. The window arrangement is not only important to the overall architecture of the building; it is also arranged to control the flow of light into the interior spaces. These four designs are not to be understood as stylistic exercises in construction or in the interaction of concrete, timber, steel and glass. They are experiments in light and reflected light as an extension of the materials available to the architect.