Ambitious building retrofits are often hardly justified by energy savings only. A previous research project has shown that dividing by two the energy consumption of a building (like a school) may lead to a return on investment superior to 25 years [RS4E, 2010]. In this configuration, decision-makers are often not inclined to invest. Thus there is a need to investigate in more details and highlight the benefits of such retrofits or new buildings with a broader point of view. That is why the DECADIESE methodology has been developed by a consortium of major construction and energy companies (EDF R&D, Bouygues Construction, Vinci Construction, Foncière des Régions) and academic partners (CentraleSupélec, Université Paris Diderot – Paris VII, Mines ParisTech) in the frame of a French research agency-supported research project (2012-2014). DECADIESE considers an extended value of a building by incorporating sustainable dimensions through externalities integration, but also by recentering the value created by a building around the benefits for its users. This paper focuses on the latter. On one hand, costs are broken down into seven usage functions, which highlights possible mismatches between functional objectives and associated amounts of money. On the other hand, the functional performance of the building is assessed thanks to 95 criteria that are then aggregated into seven usage functions scores. Once those elements identified, DECADIESE gives to a project owner the ability to compare building variants. A complete overview of the methodology is given in section 2, and the functional aspects are explained in more details. Section 3 presents the first results and a short discussion. Finally, section 4 highlights the main conclusions and perspectives.