Sustainable retrofitting of existing buildings: A comprehensive review of technologies, management strategies, and digital tools

The building sector is a major contributor to global energy consumption and greenhouse gas emissions, making energy retrofitting a critical strategy for advancing sustainability and decarbonisation. This systematic review synthesizes the current state of knowledge on sustainable retrofitting of existing buildings by integrating evidence across three interconnected domains: retrofit technologies, implementation and management strategies, and digital decision-support tools, encompassing residential, commercial, and industrial buildings. Retrofit interventions are classified into passive and active approaches. Passive measures reduce thermal loads through improvements to the building envelope, whereas active measures enhance operational efficiency through HVAC upgrades, energy-efficient lighting, renewable energy integration, and intelligent control systems. The review identifies financial, regulatory, and technical challenges as the principal barriers to retrofit implementation, while economic benefits, improved occupant comfort, and supportive policy frameworks emerge as the primary drivers. The synthesized evidence demonstrates that energy savings vary considerably depending on retrofit depth, baseline building characteristics, and climatic conditions, with deep retrofit strategies consistently achieving greater energy reductions than single-measure interventions. Furthermore, the review highlights that zero-capital operational strategies can deliver substantial energy savings but remain largely overlooked in existing policy frameworks. It also identifies a persistent gap between simulated and measured post-retrofit performance, underscoring the need for more robust evaluation methodologies and evidence-based decision-making in future retrofit projects.