New Mythenquai 20/28 Replace­ment Building – House-in-House Trans­formation
New Mythenquai 20/28 Replace­ment Building – House-in-House Trans­formation

New Mythenquai 20/28 Replace­ment Building – House-in-House Trans­formation

Swiss Re’s new Lake Mythenquai 20/28 replace­ment building is taking shape where the building by the name of Mythenschloss once stood on the beach named Mythenquai. From the previous building, only the dia­phragm walls and facade will remain. Marti Zurich is the lead con­sortium partner for the construction work.

Some 100 years ago, the original Mythen­schloss was built as a re­sidential building in an ex­clusive location on Lake Zurich. In the early 1980s, the aging original building was de­molished and re­placed with a resi­dential and office building. Only the re­con­structed neo­classical facade was left in place as a reminder of the palatial building from a former era. Some time ago, it be­came clear that the second building’s days were also numbered. Changes in the structural require­ments and a sub­stantial need for reno­vation made it im­perative that the building be re­placed.

Demolition of the old building began in the summer of 2020, and all floors above the ground level were de­molished in spring 2021. In this way, the ground­work was laid for be­ginning more complex de­molition work on the su­blevel. This second­ary work was challenging due to the nearby lake and the corres­ponding ground­water, which means that there are massive forces acting on the cons­truction site below the terrain’s upper edge. Elaborate measures were re­quired to secure the premises, such as lowering of the ground­water level and cross­wise arrangement of the struts. Before de­molition of the sub­levels could even begin, around 2,500 tons of steel had to be in­stalled. For con­struction of the new replace­ment building below ground level, it was fortunately possible to reuse the shell of the original building, more specifi­cally the diaphragm walls and facade. That is why it is referred to as the house-in-house method.

The project is ex­ceptionally de­manding and complex – and precisely the sort of challenge that inspires me!
Oliver Meier,
Project Manager, Marti Zürich

Once the builders arrived at the foun­dation of the original building, the next highly complex task was tackled. The existing base­plate was a strut plate that provided hydro­logical counter-pressure against the forces of the terrain. If this base­plate had been re­moved all at once as a single piece, the ex­cavation either would have collapsed or would have been flooded by Lake Zurich. For this reason it was ne­cessary to de­molish the existing base­plate in staggered phases in a checker­board manner. In each of these individual found­ation panels, the old baseplate was re­moved and immediately re­built at a level that was 60 cm lower. In the mean­time, the old and new base­plate segments were in per­manent contact, as this was the only way to en­sure the continuous support of the struts. After being defined and meti­culously calculated by the General Planning Team, this construction process was imple­mented according to a highly complex script, making it possible to achieve un­rivaled safety through perfect orchestration.

In the meantime, the new base­plate and two of a total of four sublevels have been completed, and the con­crete construction is progressing on the next two su­blevels. Due to the location of the con­struction site, the new project remains a challenge. The con­struction peri­meter is encircled by four roads, space is in short supply, and deliveries need to be planned on a just-in-time basis. Most people associate the name Mythenquai with strolling along the beach and engaging in carefree recreation on the lakefront. At Marti, we think of Mythenquai as a fascinating construction site.

Hard Facts

  • SIA m³: 201 730 m³
  • Concrete: 36  042 m³
  • Wall formwork: 34 525 m²
  • Ceiling formwork: 43 169 m²
  • Reinforcement: 5 347 t
  • Steel construction: 2 150 t

The stakeholders include