The growing focus on energy retrofitting of existing buildings, a key strategy for decarbonizing the construction sector, highlights the need for integrated approaches to assess environmental performance and circularity across the building life cycle. In this context, this study proposes a multi-phase methodology combining Life Cycle Assessment (LCA) and Circularity Assessment (CA) to analyze different building envelopes and typologies. The approach addresses the limitations of many sustainability assessments, which often focus solely on environmental impacts while overlooking resource recovery, component disassembly, reuse, and end-of-life management. The methodology integrates environmental and circularity indicators, providing a cradle-to-cradle perspective on construction systems and reducing inconsistencies that may arise when the two methods are applied separately. This research develops a holistic framework for building retrofitting, focusing on the building envelope due to its role in energy performance and material flows within the built heritage. Expected outcomes include the identification of key parameters influencing sustainability and circularity and development of decision-support tools for energy renovation. The framework is currently being validated through case studies, supporting the transition toward resilient, resource-efficient, and environmentally responsible energy-efficiency practices.