# The Smart Buildings Revolution: A Comprehensive Review of the Smart Readiness Indicator Literature
## 1 Introduction  
Buildings play a dual role throughout their entire life cycle, from construction to operation, demolition and end of life disposal, as energy consumers and carbon emitters [1]. The reliance on new construction alone poses a significant threat of exhausting the remaining carbon budgets [2]. The utilization of energy within buildings accounts for more than one-third of the total global primary energy consumption [3]. This is due to the incorporation of new appliances, rising comfort standards, and longer periods of indoor occupancy [4]. Reducing the environmental impact of buildings and improving their overall environmental performance are primary goals of sustainable development [5]. Buildings in Asia account for a quarter of the total energy consumption [6], while in the United States, this sector accounts for about 37% of the total energy consumption [7], in Africa for 34% [8] and in the European Union (EU) for 40% [9; 10; 11]. Furthermore, 75% of buildings in the EU exhibit inadequate energy performance, and 85% of buildings were constructed before 2000 [12]. Within the built environment, smart technologies are particularly effective in enhancing operational efficiency, energy flexibility, and occupant well-being [13]. Empirical studies confirm that digital technologies contribute to reducing operational emissions in buildings, particularly by optimizing energy use [14; 15]. The European Commission (EC) has recognized the pivotal role of digitalization in boosting the sustainability transition of EU Member States [16]. One of the primary goals of the EC by 2050 is to achieve climate neutrality [17], and the building sector is instrumental in fulfilling the EU's environmental and energy targets. To enhance building energy performance, tackle the existing building stock, and progress toward achieving decarbonized and highly energy-efficient buildings by 2050, the Energy Performance of Buildings Directive (EPBD), recast in 2024, was introduced [12]. Aligned with the EPBD's objective of expanding the transparency of individual buildings' energy performance [18], it is essential to strengthen the role of buildings in becoming both energy producers and providers of flexibility [19]. The EPBD has emphasized the significant potential for energy savings through efforts directed at enhancing building performance and associated energy efficiencies [20]. The EC has identified digitalization as a primary factor in enhancing the energy efficiency of EU Member States [16]. Moreover, the EPBD advocates for the integration of intelligence technologies and has introduced the smart readiness indicator (SRI) [10; 21]. The initial reference to these measures can be traced back to the Clean Energy for All Europeans package [22]. The \"smartness\" of a building refers to its capability to utilize information and communication technologies effectively, which allows the building to dynamically address the demands of the grid and occupants, thus improving the overall building performance and energy efficiency [18]. The general framework for calculating the smartness indicator for buildings [23], as outlined in the proposal to amend the EPBD, focuses on the following key SRI functionalities: (i) the readiness of a building to interact in the demand response with the district infrastructure and the energy system, (ii) the building's technological readiness to adapt to user requirements, specifications and the energy environment; and (iii) the readiness of a building to operate more efficiently. The SRI raises awareness of the benefits of smart building technologies, including automation and electronic monitoring of building systems such as domestic hot water, heating, ventilation, electricity and lighting [23]. Implementing the SRI framework is expected to promote technological innovation in the construction sector and incentivize the integration of advanced smart technologies in buildings.