The transition towards a decarbonised energy system, driven by European objectives such as the Green Deal and the ‘Fit for 55’ package, increasingly relies on the integration of intermittent renewable energy sources. This requires shifting from a paradigm in which generation adapts to demand to one where demand also supports grid balancing, through Demand Side Management strategies and, in particular, building energy flexibility. Given the high share of electricity consumption in the building sector and the growing diffusion of electrified HVAC systems, buildings represent a key resource for Demand Response programmes. In this context, the building envelope, traditionally considered passive, can become an active component, here referred to as an Advanced Building Envelope (ABE), capable of supporting flexibility while maintaining indoor comfort.