This multi-family building built in 1982, is the result of a retrofit intervention characterized by the change in its appearance thanks to the use of coloured photovoltaic...
building renovation
Architect Karl Viriden
`It is important to highlight that the first goal of renovation projects is to try to reduce energy consumptions as much as possible and then to design solar systems such as BIPV to provide renewable energy.`
PV camouflage

This multi-family building, built in 1982, is the result of a retrofit intervention, with a forth-floor extension, which is characterized by the change in its appearance thanks to the use of coloured photovoltaic modules which allow the facade to assume an homogeneous appearance as the “active” parts are not immediately recognizable. The PV modules have a matte surface and this causes a reduction of the solar power output by about 39% as the green/grey colour is given by the front glass.

Floor plan

Before the retrofit. Credits Viriden+Partner AG

View of the building before the retrofit

Dummy modules were used on 2% of the total surface area of the facade.

Building characteristics
  • Building typology
  • Construction type
  • Year of construction
    1982, retrofit July 2015  – August 2016
  • Energy reference surface
    2,870 m²
  • Energy index
    33.7 kWh/m²a (heating and electricity)
Architect Karl Viriden
`In order to collect feedback on this architectural design, we showed the picture of this building to an audience and we asked them if the building of the future could look like this. Surprisingly from over 3500 responses, only 5% provided negative opinions, while 77% answered that this could actually be the answer for both the aesthetical and ecological aspects in future buildings. 18% of the participants declared that electricity production is better than a nice facade because of the eco-funding.`
Active solar surface 165 m² 1586 m²
Active solar surface ratio n/a >75%
Peak power 20 kWp 159 kWp
Building skin application Flat roof Cold facade
Storage n/a n/a
Energy production
Source: Viridén + Partner AG
Building skin
  • Application
    Standard modules are laid on a metallic support system.
  • Description
    Flat roof with a layer of 34 cm of insulation.
  • U value
    0.09 W/m²K
  • Fastening system
  • Other

On the flat roof solar thermal collectors and an applied photovoltaic system were installed.

  • Application
    PV cladding integrated in a cold facade.
  • Description
    Custom-made BIPV modules in 13 different sizes + 5 types of dummies (non active panels).
    Brick walls with a layer of 34 cm of insulation.
  • U value
    0.10 W/m²K
  • Fastening system
    Continuous fixing system (aluminium tracks).
  • Other
    The presence of structural glazing sealant on the back-rails allows better absorption of the horizontal load in comparison with fixed point connections.
Installation of optimizers. Credits Viriden+Partner AG

The air cavity and thermal insulation are hidden behind the modules.

  • Application
  • Description
    Triple glazing with wooden frame
  • U value
    0.80 W/m²K
Cladding. Credits Viriden+Partner AG

The new cladding is made of “invisible” PV modules with a matte surface.

BIPV module
  • Manufacturer
    Sonnenkraft GmbH
  • Cell technology
  • Front glass type/customization
    Digital ceramic print on glass/glass BIPV modules
  • Dimension
    Custom made
  • Power
    28 – 170 Wp
  • Specific power
    110 Wp/m²
Technical details

The existing 4-storey residential building was a 2-shell masonry with an intermediate insulation of 8 cm.
For static reasons, the perimeter wall could not fulfil the requirements of the new cold facade and was therefore completely removed. The aim of the project was to develop a building envelope, which was not only the protective, aesthetic and energetic layer but would also serve as an energy supplier.

Hotspot image
Vertical section
Hotspot image
  • Total cost of the building
  • Square meter price
    1,050/m² CHF (facade cost considering materials and electrical components)
    The cost of the facade is not representative of the current BIPV market as it is a constructive element which was developed specifically within the “Pilot, demonstration and flagship project” of the Swiss Federal Office of Energy.
Building geometry. Credits Viriden+Partner AG

The realization of a BIPV facade requires the involvement of several actors at the same time.

Parties involved
  • Owner
    Private owner
  • Architect
    Viridén + Partner AG + EcoRenova AG
  • Photovoltaic Installer
    Diethelm Fassadenbau AG
  • Photovoltaic consultant
    Diethelm Fassadenbau AG
  • Façade installer
    GFT Fassaden AG
  • Photo
    Viridén + Partner AG
Awards and recognitions
  • Schweizer Solarpreis 2017

    Prixforix 2018, Award for the most attractive facade in Switzerland, Audience Award

  • Publications