The apartment building, hosting 48 flats, was built in 1970 as a modest, practically non-insulated, concrete structure. A change in the...
Apartment building
Architect Beat Kämpfen
``Sustainability and ecology are not just a marketing gag but a vital part of the concept.``
An energy makeover

The apartment building, hosting 48 flats, was built in 1970 as a modest, practically non-insulated concrete structure. A change in the apartment sizes was therefore impossible for cost reasons. Consequently the structure has been maintained with small apartments, even though it was possible to add a top storey with larger apartments. The house now comprises 50 apartments with 1 to 3 rooms.

About 60 people live in the building with a total space requirement of 35 m² per person. The demand for hot water is correspondingly high. The large closed facade areas and the removal of an exhaust air duct of the underground car park led to a new energy concept: 180 m² of thermal solar collectors integrated in the facades and a 19 m high water storage tank in the former exhaust duct. A heat pump with four geothermal probes and 150 m² photovoltaic on the roof complete the energy system. The energy colander of the past is now fully equipped for the demands of our times. The vertical solar collectors stretch the building upwards and are covered with a glass that changes its appearance from bronze to silver (Kromatix). In addition, hop plants are a guard part of the facades, making a contribution to urban ecology.

Section of the building, in red is highighted the added top storey.

View of the building before the retrofit

Interior view of the top storey.

Building characteristics
  • Building typology
  • Construction type
  • Year of construction
    1970, retrofit 2017
  • Energy reference surface
    2,132 m²
  • Energy index
    19.4 kWh/m²a (heating and electricity)
  • Energy labelling
    Minergie-A ZH-045-A
Architect Beat Kämpfen
“Our buildings aim to fit into the immediate environment and often come along with a modest appearance. They are showing that solar energy usage can be a simple, everyday issue.”
Active solar surface 230 m² 181 m²
Active solar surface ratio >75% <25%
Peak power 36 kWp n/a
Building skin application Flat roof Cold facade
Storage Water tank, storage battery 19000 lt, 20kWh
Energy production
kWh (photovoltaic)
Source: Kämpfen Zinke + Partner AG
kWh (solar thermal)
Source: Kämpfen Zinke + Partner AG
Solar Thermal
Building skin
  • Application
    Photovoltaic modules added on a flat roof
  • Description
    Flat wooden framed roof insulated with 34-46 cm of mineral wool
  • U value
    0.14 W/m²K
  • Fastening system
    Continuous fixing system (aluminum tracks)
  • Other
    On the roof there is a PV surface of 230 m² (35.7 kWp).

View of the roof with the photovoltaic installation.

  • Application
    Solar thermal collectors integrated in three facades
  • Description
    Concrete walls insulated with 22-34 cm of mineral wool
  • U value
    0.12/0.15 W/m²K
  • Fastening system
    Continuous fixing system (aluminium tracks)
  • Other

The projecting part on the northen facade was covered with the same Kromatix glass. Instead of a solar thermal panel, behind the glass is hidden the insulation layer.

  • Application
  • Description
    Triple glazing with wood/aluminium frame
  • U value
    0.70 W/m²K
  • g value
  • Other

Large windows were used in the new top-storey floor.

The existing windows have been all replaced.

Solar Thermal Collector
  • Manufacturer
    DOMA Solartechnik GmbH and SwissINSO
  • Cell technology
    Flat plate collectors with aluminum absorber and highly selective Miro-Therm coating
  • Front glass type/customization
    Kromatix Solar Glass. Multilayered coating deposited on the inner glass surface and treatment of the outer glass surface for diffused reflection.
  • Dimensions
    Custom made (variable, approx. 1120x3080mm)
  • Specific power
Technical details

DOMA FLEX large-area solar thermal collectors are located on three facades: 36m² each are located on the East and West Facades and 108m² on the southern facade. Because of the different locations of the solar collectors, energy is produced throughout the entire day. Although the vertical installation of the solar collectors reduces the yield in the summer, it optimizes the warmth production in the winter. The glass for the solar collectors are custom-made by Doma-Schweizer in Vorarlberg (Austria). They are coated with a Kromatix glass from Swissinso. The color of the collector changes from grey to bronze, depending on the angle of view and the intensity of the sun.

Hotspot image
Vertical section of the eave connection
Hotspot image
  • Total cost of the building
    6,500,000 CHF
  • Price per m³  
    850/m³ CHF

Hops is covering part of the facades, contributing to urban ecology.

Parties involved
  • Owner
    David and Ana Dubois
  • Energy specialist
    Edelmann Energie – Energie und Nachhaltigkeit am Bau
  • Engineer HVAC 
    Naef Energietechnik
  • Solar thermal installer
    Ernst Schweizer AG as well as other participants
  • Photo
    Kämpfen Zinke + Partner AG
Awards and recognitions
  • Awards
    Schweizer Solarpreis 2017 – Plus Energy Building
  • Publications
    Vom Vielfrass zum Energieproduzenten

    In: db-Metamorphose / deutsche bauzeitung 3.2019