Haus A | Duplex Architekten

A total of 370 apartments, shops, restaurants, workshops and artist’s studios, day care centres, and a guesthouses have been constructed at the Hunziker Areal in Zurich. Besides the urban master plan, Duplex Architekten have been responsible for the design of two buildings on the site, the Cluster House («House A») and the Housing Community («House M»). The vision was to create a part of the city rather than an estate.

Instead of the usual large-scale forms of rows and blocks, the urban planning concept proposes a cluster of smaller detached buildings, their close arrangement forming a system of routes, squares and open spaces with a marked urban character.

The tension-filled sequence of the outdoor spaces as well as the public-oriented use of ground floor areas livens up the quarter. Besides the ample provision of a wide variety of common areas, the quarter also requires individual places of retreat. The special characteristic of this project lies exactly between these opposite priorities: security and privacy on the one hand, and varied opportunities to engage in activities of the community on the other.

In the dialogue phase, which followed after the urban planning competition, the projects were revised by the participating architectural practices (Duplex, Futurafrosch, Müller Sigrist, pool, Miroslav Šik) according to the agreed set of rules. A variety of residential forms and floor plans is thus implemented in the Hunziker Area, which fulfil the demands on living together cooperatively in various ways.

The cluster apartments of the «House A» are a new type of modern flat- sharing community with a generous common area (living/dining) and sleeping areas each with a separate bathroom. Smaller, private apartment satellites are coupled to larger common areas. Since the kitchens and living rooms need not be fully laid out for each private unit, less space is required. As a result, shared kitchens and joint living rooms can be planned more generously. The retreat to one’s private sphere is nonetheless possible at all times because each private room also includes an individual bathrooms and a small kitchenette. This novel, communal form of living is also attractive for elderly people or single parents. Furthermore, an apartment in House A offers assisted living for people with disabilities.

The compact building shape and the decision in favour of a single-layer wall construction made it possible to achieve very low energy consumption values without additional insulation. However, the limited load-bearing capacity of the porous blocks normally allows only three to four storeys. For the six-storey building, this difficulty was solved by means of windows strictly arranged above one another, a weight-saving construction with only 20cm thick floor slabs as well as the design of a stiffening concrete core in the centre of the building.

Thoughts about the construction

The single-layer wall construction or more precisely speaking, the used Porotherm clay block was introduced to the project during the feasibility analysis in 2010. At that time, the building block was rather unknown in Switzerland. We came across a product brochure by chance and presented the idea to the clients, who supported us immediately. From that moment on we have tried to give this project a «clay block- suited» design.

One of the challenges was to observe the maximum pressure resistance of the building block. The recommendation by ZZWancor was specified as 3-4 storeys, whereas we had planned six levels. So we started to reduce weight:

Since the building should be built of brick, we reduced the number of concrete walls to four earthquake-proof walls, which simultaneously form the staircase. In order to reduce the thickness of the floor slabs, the span is restricted to slightly more than 6 metres. The cells of the floor plan concept provide the load-bearing structure.

Owing to the ventilation systems required today for buildings with favourable energy consumption, the thickness of floor slabs is usually not determined by the span but the building services placed inside them. Today, specialised technical planners demand a floor slab thickness of 26cm, so that acoustic specifications for ceilings with ventilation ducts and their intersections can be complied with. We have removed the ducts from the ceilings, rearranged the vertical ducts and laid out the air circulation by applying a kind of cascade principle. The floor slab thickness could thus be reduced to 20cm. Related to all storeys this equals a whole floor slab with a thickness of 30cm.

In the next step, we introduced a building block format into the planning. This was no requirement and caused a surprise when we first announced that we wanted to re- plan the building according to the block format. We had two reasons to do so: firstly, we had initially planned to leave the pattern of the building blocks visible on the façade and only protect the brickwork through, for example, whitewashing. For technical reasons, however, this was not possible. The brick is too porous and absorbs water. Secondly, it was obvious that it would probably be painstaking to cut such a big and heavy brick. By revising the layout according to the block format, we were able to plan storey heights, wall lengths and window dimensions to fit. The exterior wall was thus divided into wall segments, for which - with the exception of ceiling front areas - not a single stone had to be cut.