*4.3. Discussion*

In this study we analyzed multiple factors that influence the realization of EERM in owner-occupied single- and two-family houses in Germany. The specific subjects of our empirical analysis, which is based on a relatively highly educated sample, were owner-occupiers of single- and two-family houses who stated their intention to conduct EERM ("Future-Refurbishers") and those owner-occupiers of such houses who stated a need to undertake EERM but do not intend to take action ("Non-Refurbishers").

Utilizing an extended version of the TPB as a framework for our analysis appears justified in our point of view as it has already been previously used successfully in the context of buildings and energy efficiency and factors of all predictor domains contribute to group differentiation in our study. Additionally, Wilson and Dowlatabadi [45] state, that "Residential energy use is characterized by a wide range of decision types and contexts, as well as psychological and contextual influences on behavior. [Thus] Decision models from different research traditions are all relevant to some aspect of residential energy use". Adding further aspects in connection with the original TPB is not unusual and provides, as Kastner and Stern [18] state, the possibility to improve and adapt the purpose of the analysis. Additionally, considering house owners' perceived specific *Building conditions* and *Environmental awareness* in this study contributed to a better differentiation of "Future-Refurbishers" and "Non-Refurbishers".

Before discussing the results of our study some limitations and methodological aspects need to be addressed. As outpointed earlier, our data was collected with an online survey in June and July 2016. Choosing this time of the year might have led to a bias of our results due to an omission or an overrepresentation of certain house owners. Evidence for such effects can be found in [46]. Additionally, some limitations refer to the depth of further statistical evaluations, e.g., carrying out a more detailed analysis of our research framework differentiated by older or younger respondents in interaction with their income. The reason for not realizing such type of analysis relates to the limited sample size. Even though the number of respondents was suitable for the statistical analyses presented, the sample size was not sufficient for such more specific statistical analyses. The limited sample size was also the reason why further statistical tests to underpin the predictive power (e.g., cross-validation; for details see [47]) were omitted.

Related to our results, specifically referring to the considered *Behavioral beliefs*, the literature states that individuals are likely to perform energy efficiency measures in order to increase indoor comfort and to reduce energy bills and their environmental impact [32]. However, the results of our study regarding the last aspect suggest the opposite as the perception that EERM do have a positive effect on the environment is more characterizing for the group of "Non-Refurbishers." A reason for this result could originate from house owners' thoughts about the necessary building components and the origin of the materials for these components that are required for carrying out EERM. While "Non-Refurbishers" might only consider the usually desired positive effects of EERM on the environment, "Future-Refurbishers" answers could be influenced by their higher involvement and know-how about the refurbishment such as the necessary amount of insulation material or construction material for windows and doors, which are often based on fossil fuels. Regarding the factors *Indoor comfort* and *Energy bills,* our results are congruent with the thesis of Organ et al. [32]. Further underpinning results referring to these aspects originate from empirical studies conducted in Ireland [48] and Sweden [49]. The Irish study concluded that EERM are mainly driven by monetary goals while comfort gains were identified to be of secondary relevance. Environmental benefits of EERM were identified to be of low relevance in both studies. In terms of *Doubts about desired e*ff*ects,* our results go along with the cause-effect relationship stated by Zundel and Stieß [19] who identified doubts concerning the results of EERM as a hindering aspect.

Regarding the *Normative beliefs,* our results associated with the factor *Esteem friends*/*family* indicate that a supportive opinion of friends and family favors the uptake of EERM, what is supported by Earl and Peng [50] who state that the desire of an enhanced standing within the social surrounding (e.g., friends and family) is a motivating factor for the uptake of EERM. Furthermore, a case study carried out in British communities [51] also suggests that 'social capital' is important for home energy innovations what partly is related to the wish of individuals to gather information from people they know—e.g., from friends or family members who value such home energy innovations or EERM.

When considering *Control beliefs* and the factor *Financing problems*, our results go along with Organ et al. [32] and Zundel and Stieß [19], who state a lack of financial resources as a barrier for energy efficiency measures. Concerning the factors *Consulting during conduction* and *Consulting during planning*, our results indicate that a refurbishment is more probable in the case of a low demand of professional help or advice. This could be influenced by the house owners' *Own capabilities*, but also by low trust in energy advisers. Support for the latter reason can be found in the study of Risholt and Berker [52] who identify a lack of knowledge and expectation of bad advice from professionals as impeding aspects for homeowners. Lacking possibilities to conduct EERM by themselves is also stated as impeding factor in our study. A further result in the field of the *Control beliefs* shows that high availability of time results in a higher probability of realizing EERM (*Time conduction, Time planning),* what is in line with the findings of Zundel and Stieß [19] who show that house owners who conducted EERM have had more time to deal with the planning than those who conducted standard refurbishment measures. A higher time intensity for larger home improvement projects is also outlined in [53]. Further support for our findings can be found in empirical studies conducted in Greece [54], Norway [55] and The Netherlands [56]. In the latter two studies financial aspects were also identified as barriers for the adoption of EERM. Moreover, in [54] a missing expertise or knowledge was identified as an impairing factor, too. Further critical influencing factors identified were a lack of reliable experts and information, time and effort to find information and complexities in the refurbishment process. The latter aspects found in [56] do not only support our finding regarding the relevance of time to carry out EERM but also our findings referring to the trust in energy advisers.

Besides the TPB components we also analyzed *Environmental awareness* aspects in the study on hand. From six initial factors, only the factor *Impacts of decisions* was identified to contribute significantly to a differentiation of "Future-Refurbishers" and "Non-Refurbishers." This factor indicates that individuals who do not put high relevance on environmental aspects during decision-making rather belong to the group of "Non-Refurbishers." When additionally considering the results associated

with the factor *Reasonable for environment*, both findings together allow for the conclusion that even though "Non-Refurbishers" might support the idea that EERM are good for the environment, it might be less likely that environmental aspects are of high relevance during the decision-making in terms of EERM for this group. This conclusion suggests to regard political initiatives critically that emphasize the environmental benefits of energy-related refurbishment activities to influence house owners' decisions positively in order to persuade them to conduct EERM.

When considering the predictor *Building conditions*, our analysis shows that the perceived *Energy e*ffi*ciency* as well as the *Comfort and visual appearance* strongly contribute to a differentiation between the analyzed groups. At a first glance, it is reasonable that those house owners who perceive a greater need for actions belong to the group of "Future-Refurbishers." However, when considering the construction periods of the houses of the analyzed groups, it comes up that the houses of "Non-Refurbishers" are on average older compared to those of "Future-Refurbishers" and thus should generally call for a higher need of action. Taking into account the finding of Stieß and Dunkelberg [20] who conclude that house owners with standard refurbishment measures are more likely to believe their house to be in a good condition, this might support the assumption that the actual (energy) status of the houses of "Non-Refurbishers" is more negative than perceived by their owners even though they have performed some efforts to reduce the energy consumption of their houses in the past.

German and European goals and legislations have become steadily more important to fulfill the *Legal requirements* in the context of EERM. Our results suggest that a future refurbishment is more likely the lower the perceived problems are to comply with existing regulations. According to the review of Kastner and Stern [18] neither approving nor disproving results could be detected in the existing literature for this factor.

Further initially surprising results refer to the variables *Complex promotion* and *Appropriate craftsmen.* Our findings suggest that house owners are more likely to belong to the group of "Non-Refurbishers" if they think it is easy to find appropriate craftsmen for carrying out EERM or if they do not perceive governmental promotions as complex. These results might be explained by the low involvement and experience of "Non-Refurbishers" related to the practice of refurbishment activities. Thus, such house owners might not be very concerned when it comes to aspects as finding craftsmen or dealing with governmental promotions. This might originate from a lack of a threat of "Non-Refurbishers" compared to house owners who intend to undergo EERM and who not only risk losing time but also money, due to potential incorrect craftsmen-work, missed grants and subsidies because of non-compliance with legal requirements. This reasoning is supported by Pepels [57],who points out that extensive investments (such as in EERM) are associated with more extensive risk evaluations or intensified search for information.

## **5. Conclusions**

In order to increase the currently rather low energy efficiency-related refurbishment activities in Germany it is necessary to take a wider range of measures into account. While it is widely acknowledged that private house owners and their respective buildings play a key role for achieving the climate targets until 2050 set by the German Government [4] and elsewhere, the results of this study show that pure political appeals to house owners to conduct specific energy-related measures are not expedient.

Based on the results of our analysis and with respect to our second research target, we suggest that, along with already existing financial support *(Financing problems)* that was identified as relevant, an increased non-monetary support might supplement existing efforts to trigger individual house owners towards increased energy-related refurbishment activities. An enhanced presentation of refurbished "best-practice houses" and their owners, who already have mastered the task of refurbishment, could be such an additional non-monetary support activity.

These kind of measures could supplement existing information and capacity building measures that are provided by the German Energy Agency (Dena, "Deutsche Energieagentur") or the KfW ("Kreditanstalt für Wiederaufbau"), which support interested house owners inter alia during financing EERM activities. An enhanced provision of best-practice houses could be provided by regional contact points for energy efficiency or by the German Energy Agency itself, as their objectives involve the design of campaigns in the context of energy efficiency, the distribution of information to the public, and the support of the building sector (architects, craftsmen, etc.) in order to ensure aligned work with current standards and regulations [58].

Directed towards "Future-Refurbishers," a presentation of already refurbished houses in collaboration with energy advisors and craftsmen could be used to level up the currently low refurbishment efficiency in the residential building sector in Germany. Since our results indicate a rather low acceptance of advice from professionals (*Consulting during planning, Consulting during conduction)*, providing more neutral information during such best-practice events could foster additional efforts from those house owners who already intend to take specific individual energy-related refurbishment measures. Thus, potential doubts (*Doubts about desired e*ff*ects*) about the implementation and the effects of additional measures of "Future-Refurbishers" could be eliminated. A key role in this regard is assigned to the owners of the refurbished best-practice houses. While professionals could take care of the presentation of the individually conducted measures and the overall refurbished building, or answer specific questions from the visiting house owners, these hosting house owners could ensure the trustworthiness of the professionals and provide further credible answers. Besides information on promised and actual costs and energy savings, those owners can also provide reliable information on technical aspects such as the effort associated with technical systems (e.g., in terms of operation and maintenance aspects) or the refurbishment process itself.

Such a trustworthy and informative situation can also be used to inform and persuade house owners who are aware of energy-related deficiencies, but also perceive financial problems (*Financing problems*) and thus neglect the uptake of efficiency measures. By lowering these house owners' doubts regarding financial savings or costs associated with certain efficiency measures, this could also reduce these house owners' perceived financial problems. Additionally, information on technical aspects provided by the professionals but also the best-practice-house owners can also lower their concerns due to a perceived lack of skills and capabilities (*Own capabilities)*.

A further promising activity could be providing Do-It-Yourself workshops to individual house owners. During such workshops, energy advisors and craftsmen could present measures that allow for identification and removal of energy-related weak points of residential buildings. This could involve for example, the insulation behind radiator niches, or, for technically skilled house owners, the insulation of neuralgic spots like cellar ceilings. In addition to the direct effect of such measures, meaning the provision of capabilities and skills (*Own capabilities*) to "Non-Refurbishers" but also "Future-Refurbishers," there are also indirect effects connected to such workshops, i.e., multiplier effects among house owners, since applied know-how very likely will be spread within the neighborhood and among friends (*Esteem friends*/*family*). Additionally, such workshops might have positive effects related to trust in and the image of EERM since "Future Refurbishers" as well as "Non-Refurbishers" are likely to look for approval from their social network (e.g., families, friends, neighbors) instead of trusting highly unknown governmental or professional experts.

Workshops of this nature can also be used to provide information on legal obligations (*Legal requirements*) that have to be met according to the German "Energieeinsparverordnung" (energy saving ordinance) when implementing specific EERM. Other relevant information could concern e.g., legal obligations, when old or polluting heating systems need to be replaced. In addition to "Non-Refurbishers" and "Future-Refurbishers," another group of house owners could be targeted with such workshops, namely those who are basically not aware of the energy efficiency of their houses. By providing information on average energy consumptions for houses of different construction periods as well as information on energy savings associated with different kinds of EERM, all groups of house owners could be triggered to re-evaluate their actual need for energy efficiency measures and their intentions to take measures. This is also true for "Non-Refurbishers" who perceive a lower

need for actions (*Building conditions*) but live on average in older houses with mostly lower energy efficiency standards.

A further opportunity associated with the presentation of best-practice refurbishment projects is the possibility to allow visiting house owners to experience a high level of indoor comfort and the nice appearance of a comprehensively refurbished building envelope. Such measures would address important influencing factors according to our results such as *Building conditions* and *Behavioral beliefs* and the factors *Comfort and appearance* and *Indoor comfort,* respectively.

Even though the extent and the effects of best-practice campaigns in private residential houses might be unknown, the realization of the proposed measures is a way forward to increase the energy efficiency in the existing building stock in Germany but also in other European countries. Furthermore, this kind of initiative would largely go along with Article 17, information and training, of the Energy Efficiency Directive 2012/27/EU [2], which demands that "Member States shall, with the participation of stakeholders, including local and regional authorities, promote suitable information, awareness-raising and training initiatives to inform citizens of the benefits and practicalities of taking energy efficiency improvement measures."

Due to the initially mentioned fact that a large share of single- and two-family houses is located in cities and urban districts, such measures might be especially promising when focused on these spatial and social environments. Since financial issues, capabilities and social acceptance were identified as relevant, enhanced initiatives considering these aspects could help to reduce the high energy consumption and GHG emissions in such conurbations. Thereby, the mentioned focus on specific districts is essential. Besides the possibility to enhance the outlined multiplier effect in the regional social surrounding, also regional-typical energy-related weak points of the commonly similar buildings could be addressed. These weak points could be covered during the mentioned practice-orientated workshops as well as in funding programs, e.g., for subsidized refurbishment management or for specific EERM. Increasing prices because of such funding programs, however, could be prevented by contractual arrangements with regional partners.

Nevertheless, the potential negative effects of such local initiatives also need to be considered, e.g., the fact that people with lower incomes might not be able to afford living in such houses or apartments anymore due to increased rental fees after refurbishment activities. Overcoming this phenomenon, however, is another aspect that is and needs to be considered by politicians and also scientists [59].

**Author Contributions:** Conceptualization, methodology, statistical analysis, writing—original draft preparation, writing—review and editing: R.B. supervision, project administration, funding acquisition: T.D., K.M.

**Funding:** This work was supported in part by a grant provided by the Bavarian State Ministry of Education, Science and the Arts [project number 1512-DW-78-01].

**Conflicts of Interest:** The authors declare no conflict of interest.
