Space-effective frame construction in a rigid grid in one of the largest timber buildings in Switzerland
Cantons of St. Gallen and Thurgau, represented by the Canton Building Department of St. Gallen
Staufer&Hasler Architekten BSA SIA, Frauenfeld/CH
J.Siegfried Holzbauplanung, Roggwil; Ingenieurbüro Marcel Nobel AG, Wil; Conzett Bronzini Gartmann AG, Chur
The very announcement itself of the two-phase competition held in 1997 for a new canton school in Wil, Switzerland, requested that timber be used as the building material. In the winning design, the architects arranged the extensive spatial programme around a central, tree-filled courtyard in a compact, graduated volume ranging from two to four storeys. The entire building is conceived as a timber frame structure based on a strict grid of 3.90 x 5.40 metres. Four concrete cores, which hold both staircases and the necessary wet rooms, organise the building in accordance with fire protection requirements while at the same time providing supportive bracing. Larger rooms such as the sport tract or auditoriumwere spanned without interim supports. Following strict structural logic, the rooms with the largest spans are all set at the top of the building and hence have comparatively low roofloads to carry. Also interesting is how the jointing of the support structureof glue-laminated timber has been arranged in almost a textbook manner. The posts carrying the heavy loads are joined with the end-grain. The main beams are slit into deep studs and the joists notched in outside the main load-bearing axes. In this way, the natural properties of the material of wood are ideally exploited, eliminating the necessity for complicated joints. The treatment of the facade is similarly consistent: here, solid oak was chosen, which has demonstrated good durability in exterior use. In order to keep maintenance costs down, the wood was left untreated. The measures selected for protecting the timber used in the construction keep the critical areas of the facade damage-free, while profiles that project from the building volume minimisewith their play of light and shadow the unavoidable traces of weathering on the wood. In both the design and construction of the Canton School in Wil – one of the largest timber buildings in Switzerland – the special qualities of timber as building materialhave been utilised in an exemplary fashion.