Handcrafted, natural materials and refined construction techniques are combined to create a quiet sensitivity
School pavilion Allenmoos II
The projects of Roger Boltshauser appear to work and re-work the same small number of themes, forms and materials to an extent that other architects might tire of, but which in his case have produced a consistent oeuvre of quiet sensitivity.
Simple orthogonal buildings with a reduced formal articulation are constructed using rammed earth and/or in-situ concrete together with glass bricks and box skylights. These limited means have allowed Boltshauser to carefully refine particular construction techniques, providing a sensuous palette of handcrafted, natural materials.
All these elements are present in his latest work, Schulpavillon Allenmoos II, a renovation of a 1958 school building in Zurich. The new building retains the existing foundations and basement along with some of the above-ground structural walls but is otherwise newly constructed, although a precondition of the development was that the footprint and height of the previous building must be kept to.
Source: Beat Buehler
New elevations are clad in stone tiles provided by Petersen, and a new green roof is punctured by a strip of clerestory lighting.
The plan is extremely simple, featuring a series of classrooms with connecting doorways at the front and a shared space to the rear. The central spine wall steps in and out, allowing the linear box skylight above to provide high-level light to both front and rear spaces. A thin clay/casein mixture has been applied to internal wall and floor surfaces.
Source: Beat Buehler
Critical in defining the architectural character of the building is the loggia, constructed of rammed earth, forming a new front that frames views from the classrooms out to the neighbouring small park. The shallow depth of the loggia space and the generous width of the verticals create a subtle ambiguity as to whether this is a colonnade or a broken wall, and reveals the architect’s continuing interest in the threshold between outdoors and indoors as a moment of critical architectural importance.
The use of rammed earth has been almost a constant within Boltshauser’s work, culminating in the construction of a new house in 2008 in Schlins, Austria, for Martin Rauch, one of Europe’s leading specialists in earthen construction.
While that building provided an essay in the various possible uses of earth within building construction, the school pavilion isolates the loggia piers as the single rammed earth element, massive in contrast to the supported thin slab, and visually associated with the main body of the building through the use of protruding courses of stone tiles of the same type as used for the external walls generally. These courses are increasingly spaced as they rise towards the roof of the building and shed water from driving rain away from the earth surface, thereby reducing the erosive impact.
The piers have been constructed using similar processes to those developed in the Rauch House walls; no reinforcement was used, the strength coming purely from compaction and the binding of loam to stone.
Similarly, no surface treatment was used; the fine loam content is washed away soon after construction so that larger rock granules are left to stabilise and slow the erosion process.
Architect, project manager & main contractor Boltshauser Architekten
Client City of Zurich
Structural engineer BKM Ingenieure
Services engineers Mühlebach Partner, Haerter & Partner,Walter Salm, Meier & Partner
Facade Howoldt Metallbautechnik
Landscape architect Schmid Landschaftsarchitekten
Windows & doors supplier Ziltener Metallbau
Photos: Beat Buehler