The staircase as a solid timber construction

Conradin Clavuot: School in St Peter (CH), 1998

Systems in architecture

Fig. 45: The ends of the steps

Fig. 46: General view of stair

Fig. 48: Longitudinal section

The interior of the school in St Peter is determined by the material presence of the pine beams in log construction. The design of the staircase blends seamlessly into this constructional concept. The steps are made from untreated beams which appear to grow out of the module of the solid timber wall, running between wall and balustrade. While the steps were shown let into the wall in the early drawings (see Fig. 49), this was not carried out on site because the solid timber wall is one of the shear walls of the building whose structural action would have been interrupted by the inclusion of such members. The support on the wall side was therefore accomplished with a mortise and tenon joint additionally secured on the far side of the wall with metal bolts (see Fig. 48). The steps are suspended on bolts (concealed by dummy tenons) from the balustrade, which is also made from solid timber members and spans the distance between the floors. The individual members of the balustrade are joined by a number of threaded bars so that the balustrade acts as a deep beam and can span the full distance between floors.

Solid timber undergoes contraction and hence settlement in the first years of the life of a structure. In this school the settlement per storey was up to 10 cm. This resulted in the balustrade, which runs between the floors, undergoing a minimal (calculated) rotational movement. That in turn subjected the steps to a certain amount of torsion because their two supports were each subjected to different movement caused by the settlement. This factor and the contraction of the individual components of the staircase has led to small but noticeable gaps between the individual timber components. However, this in no way impairs the overall character of the construction. The elegant rawness of the solid components easily accommodate this phenomenon; indeed, it tends to emphasise their expressive character.

Fig. 47: Section

Fig. 48: Longitudinal section

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