A pioneering retrofit first, retaining and reusing as much of the existing facade as possible; preserving intricate detailing whilst extending the life of a building.

Building V of UNESCO Headquarters is undergoing a major transformation after its first 55 years of operation and forms part of a pioneering pilot glass recycling project. The office building, designed in a creative partnership between the architect Bernard Zehrfuss and the engineer Jean Prouvé, must be brought up to current energy performance standards without exceeding the schedule or budget. Eckersley O’Callaghan, as part of a team including PATRIARCHE, won the competition with a simple ambition that respects its architectural heritage by reusing the existing facade.

These facades bear witness to an innovative and pioneering era in many respects: recycling of flat glass (architectural products such as windows and doors), prefabrication in the workshop, an innovative block curtain wall system integrating comfort ventilation, thermal insulation, solar protection, access for maintenance and above all a facade whose kit of parts approach initiated and accommodated our reuse process.

The UNESCO project will test a more circular approach for flat glass where the existing glass panels will be carefully removed and transported to a glass recycling factory and remanufactured into internal glass partitions for the building.

Our objective was to create a new thermal skin by inserting itself between the existing skin and the period structure, while minimizing the visual impact of this adaptation. A systematic verification of the carbon footprint of our design iterations was carried out, leading us to propose a wood frame wall to ensure thermal, sealing and safety performance. The existing aluminum elements – cheeks, gratings, consoles and frames – are refurbished and come to dress the new facade. This reuse resulted in a gain of 500 tCO2eq. Added to this is the recycling of approximately 113 tonnes of existing glazing, which saved 34 tCO2eq.

Paris, France