**2. Research Framework of the Study**

This section conveys the theoretical research framework of our analysis, including an introduction of the Theory of Planned Behavior (TPB) which is the main guideline for the identification of relevant factors within the scientific literature. This section also introduces additionally considered predictors which were identified when screening relevant literature.

Built upon the Theory of Reasoned Action (TRA) [29], the Theory of Planned Behavior was developed by Icek Ajzen [30]. This was done by adding the predictor 'Perceived behavioral control' to the TRA predictors 'Attitude toward the behavior' and 'Subjective norms' [14]. With these predictors, the TPB is intended to deal with behaviors over which people have incomplete control. In the context of the TPB, the predictor 'Attitude toward the behavior' refers to the extent of which a person has a favorable or unfavorable evaluation or appraisal of the behavior in question. The second predictor is named 'Subjective norm'. This predictor refers to the perceived social pressure to perform or not perform the behavior. The third factor is the degree of 'Perceived behavioral control' and refers to the perceived ease or difficulty of performing the behavior and it is assumed to reflect past experience, individuals' resources and related anticipated barriers. In general, the greater the 'Perceived behavioral control' and the more favorable the 'Attitude' and 'Subjective norm' with respect to a behavior, the stronger is an individual's intention to perform the behavior in question [14]. Thereby, the individual contributions of the three predictors are expected to vary across situations and behaviors [14].

However, according to Ajzen, the developer of the TPB, and Driver [31], the TPB postulates–at the most basic level of explanation–that performance or non-performance of behaviors depends on the beliefs behind the introduced TPB predictors. In addition to *Behavioral beliefs*, which are assumed to affect the predictor 'Attitudes toward the behavior,' these are *Normative beliefs* and *Control beliefs*. While *Normative beliefs* constitute the underlying determinants of 'Subjective norms,' *Control beliefs* refer to the predictor 'Behavioral control' [31].

Based on the TPB we utilized factors associated to these beliefs for the differentiation of "Future-Refurbishers" and "Non-Refurbishers". These factors as well as additional contextual aspects were identified by a screening of the existing scientific literature. The identified additional aspects refer to individuals' *Environmental awareness* and *Building conditions*. The latter were also considered by Organ et al. [32] as important for understanding house owners' motivation in the context of EERM. In addition, Black et al. [22] also pointed out a building's physical structure as relevant in the context of capital investments in residential energy efficiency. Considering of house owners' *Environmental awareness* in the analysis is supported by two reasons. The first relates to the interaction of energy consumption and environmental damages and the perceived high relevance of environmental and climate protection in Germany but also other European countries [33]. The second and more important reason is the identified relationship between environmental awareness and related attitudes in previous empirical research considering the adoption of measures to reduce the environmental impact of buildings [34,35]. Thus Rajaie et al. [36] explicitly suggest that environmental awareness should be addressed in research that considers technological advancements for the reduction of the energy demands of buildings and consequently their impact on the environment.

Finally, a legitimization for the utilization of the TPB as a basis framework can be found in the studies of Wang et al. [37], Wu et al. [38] or Abrahamse and Steg [39], in which the TPB was already used successfully in similar contexts (energy efficiency and buildings).
