Built between 1963 and 1971, the Lignon satellite precinct in Geneva (Georges Addor, Dominique Julliard, Louis Payot, Jacques Bolliger architects) is regarded as the most spectacular housing development in post-war Switzerland. The heritage protection agencies in the Geneva Canton have recognised the value of this emblematic scheme – urban, architectural, technical and social - with a conservation plan (plan de site) for the Lignon put in place in May 2009. This affords protection within the urban setting and seems adequately to meet the objective of conservation of the ensemble - the preservation of the architectural unity of the buildings, the planning design and the landscape quality of the exterior spaces - without having to resort to a listing in the Monuments Inventory, something which would impose major constraints on a precinct which blends social housing units with owner-occupied dwellings. For some it is an energy-guzzling black hole, for others an historical monument; either way the Lignon is under scrutiny. Given the rash of unauthorised modifications that have been made, and faced with new imperatives to reduce energy consumption whilst at the same time endorsing the conservation plan, a pilot project in the area of "preventive conservation" of the Lignon facades has been devised. For this, two Canton of Geneva agencies - the Heritage and Sites Bureau and the Energy Service, have teamed up with the Lignon Central Committee, the association representing building owners. The École Polytechnique Fédérale de Lausanne has been tasked with carrying out the research, which will look at economic, architectural and energy efficiency aspects of the site.