Buildings energetic retrofit is key to the Swiss « 2050 Energetic strategy », but the refurbishment rate is low. eREN [1] has analysed the 20th century multi-dwelling housing stock in Western Switzerland from a constructive point of view and developed refurbishment scenarios for the envelope of 10 buildings. The goal is to achieve balanced solutions between energy efficiency, constructive feasibility, building physics, cost, architecture and use value. Our investigation shows that “wrapping” is not the only solution to meet the standard, whatever the solution it is technically complex, the cost are high but could be mitigated, projects must be led by qualified professionals and interdisciplinarity must be actively promoted.