The development completed by Heim Kuntscher Architekten just north of the city centre is a pertinent example for this type of densification. Three years ago, the courtyard at 28 Zieblandstrasse was occupied by single-storey garages. In the meantime, they have been removed to create space for a three-storey apartment building. A single-carriage stairway positioned along the windowless, north-facing rear wall provides access to the three apartments (or four if the middle one is separated into two smaller units). The upper storey floor plan is almost symmetrical, with a bathroom at either side of the staircase and a long corridor in-between. The rooms are arranged alongside the southern facade. The partition walls are made of plasterboard to allow for greater flexibility for future needs. The corner rooms in the upper floor apartment are particularly spacious. Despite their depth of seven metres, they are light and airy thanks to the floor-to-ceiling windows. The central rooms are slightly smaller since they have been set back to create a loggia zone.
The loggias function as intimate retreats, which the residents have furnished with tables and chairs. The semi-opaque balcony parapets also contribute to increased levels of privacy. Like the facade cladding, they are made of spruce battens, which were coated with white silicate paint before being installed.
Hybrid construction
The timber cladding envelops a hybrid construction made of brickwork, cross-laminated timber and a larch glulam framework. Before the superstructure could be erected, elaborate foundation work was required: in order to reach stable ground, the foundation piles had to be sunk down to a depth of eleven metres. The ground floor slab is made from reinforced concrete and a U-shaped boundary wall made of insulated blockwork is built above the ground piles. The wall is stabilised by concrete peripheral tie beams at each level of the building. The double garage incorporated in the ground floor is also made of brickwork and concrete.
The bulk of the building is a timber structure. Cross-laminated timber panels made of spruce with industrial-grade finish are used for the floors and the load-bearing interior walls. The loggia zone is supported by a separate structure made of larch glulam columns and beams. The few closed facade areas incorporate full-storey prefabricated cross-laminated timber elements. The floor panels do not tie into the blockwork walls, but are supported by neoprene-lined steel brackets, which are fixed to the concrete peripheral tie beams.
The dark-oiled parquet flooring, the cross-laminated timber ceilings and white plasterboard wall surfaces offer a pleasant contrast in the rooms. There is a similar triad of colours in the loggias where the white balcony parapets, the black metal cladding of the balcony doors and the larch floorboards harmonise well.
District heating and decentralised ventilation
In order to meet the German KfW-40 standard, passive house components have been used throughout the building envelope. The energy for heating and hot water is supplied by the local district-heating network. All rooms in the residential building are fitted with an underfloor heating system. Every apartment is equipped with its own decentralised ventilation unit with a heat recovery system that meets passive house standards. The technical equipment is accommodated in plant rooms located close to the staircase. Fresh air is drawn in from the roof and distributed to the rooms via air ducts that are accommodated in the suspended ceilings of the corridors.
