**1. Introduction**

Energy efficiency in the building sector plays a crucial role in Germany and in other European countries. Both Germany and the EU have passed several laws and regulations to improve the energy efficiency of buildings. As examples the 2010 Energy Performance of Buildings Directive [1], the 2012 Energy Efficiency Directive [2] of the European Union, the German National Action Plan on Energy Efficiency [3] and the German Federal Government's energy concept [4] can be mentioned. The stipulations and objectives in these frameworks deal with the high energy demand of the existing building stock and consequently its negative effects on the climate as well as the environment. In total, the European building stock accounts for 40% of the European final energy consumption as well as 36% of the overall European greenhouse gas emissions (GHGE) [5]. For Germany, these figures are similar, with the total building stock accounting for 38% of the final energy consumption and 30% of the overall GHGE [6]. In order to achieve significant reductions in consumption and emissions, the stock of owner-occupied single- and two-family houses is of special importance in Germany. Compared to the more complex ownership structure associated with multi-family houses, owner-occupiers of singleand two-family houses are more independent in their decision-making related to energy efficient refurbishment measures (EERM) [7]. Additionally, these house owners are responsible for 11% of the

total final energy consumption in Germany what also suggests a high energy saving potential [8]. Based on an average energy consumption of 177 kWh/m2·a, the estimated potential savings could range between 50% and 70% by 2050 [6].

However, despite several governmental actions such as setting legal requirements, grants or low interest loans [9], the refurbishment rate in Germany has currently not yet reached the politically focused target value of 2% p. a. [4,8]. With regard to residential buildings, Rein and Schmidt [10] actually point out a decline of more than 6 billion Euros between 2010 (EUR 40.9 billion) and 2014 (EUR 34.8 billion) in the financial investment in EERM.

In order to achieve an almost climate-neutral building stock by 2050, as determined in the existing German regulations, and moreover benefitting from multiple societal benefits (e.g., decreased energy import dependency, lower residential energy bills and increased residential comfort [11–13]), a better understanding of house owners' reluctance towards EERM is essential. Against this background, the present study considers owner-occupiers of single- and two-family houses in Germany with a specific focus on two groups of owner-occupiers. Next to owner-occupiers who stated their intention to conduct specific EERM in the next years, hereinafter called "Future-Refurbishers," the second group consists of "Non-Refurbishers", who stated a need for EERM but also a lack of intention to take action. For the comparative analysis of these groups we analyze data gained from an online survey. Within this survey we considered influencing factors derived from the scientific literature which are related to the Theory of Planned Behavior [14], Building conditions and individuals' Environmental awareness.

Based on this research framework, our research target is the identification of those factors allowing for a differentiation and consequently a better understanding of "Future-Refurbishers" and "Non-Refurbishers" (research target 1). Furthermore, we intend to provide ideas on how relevant identified factors can be utilized to trigger increased energy-related refurbishment activities among owner-occupiers of single- and two-family houses in Germany and beyond (research target 2). This is of special relevance for cities and urban districts where globally 70% of all GHG originate from [15] and where 57% of all single-family houses are located in Germany [16].

By focusing on willing house owners pre-refurbishment ("Future-Refurbishers") and house owners who do not intend to take actions despite a perceived need ("Non-Refurbishers"), this study is a contribution to the still lacking understanding of decisions regarding EERM [17]. In contrast to our study, which is focused on future refurbishment activities, the existing decision-making literature focused on EERM is, as pointed out in the review of Kastner and Stern [18], primarily characterized by studies considering past decisions (retrospective studies) or experimental/hypothetical approaches. As examples the retrospective studies of Zundel and Stieß [19], Stieß and Dunkelberg [20], Michelsen and Madlener [21] or Black et al. [22] can be mentioned. Experimental/hypothetical approaches are followed in the studies of Achtnicht [23], Achtnicht and Madlener [24], Grösche and Vance [25] or e.g., Alberini et al. [26].

In [19,20], the authors pursued a comparative concept by comparing German homeowners with different refurbishment activities, i.e., energy-efficient and standard refurbishment activities. Michelsen and Madlener [21] also conducted an analysis among German homeowners but with a focus on motivational factors that influence the decision-making in the context of residential heating systems. In the study of Black et al. [22] various energy-related efficiency measures were considered in order to investigate relevant factors that determine the decisions of the analyzed US citizens. Next to insulation activities also activities referring to the heating system were considered.

As a prominent experimental/hypothetical approach, the analysis of Achtnicht [23], who conducted a choice experiment among German house owners, can be mentioned. Besides the role of environmental benefits, this study also analyzed the willingness-to-pay for CO2 savings. The study of Achtnicht and Madlener [24] is a continuation of Achtnicht [23] and differs with regard to the considered choice sets. Grösche and Vance [25] analyzed data of German homeowners who conducted one or more EERM (e.g., roof insulation, façade insulation, replacement of the heating system or replacement of windows). Based on this measures and further details, the authors elicited the households' willingness to pay per

kWh saved. Alberini et al. [26] surveyed Swiss owner-occupiers of houses that haven't been renovated in the past years. The considered owner-occupiers had to choose between hypothetical refurbishments during the conducted conjoint choice experiments. These refurbishments were defined by different attributes such as upfront cost, rebate offered by the government or savings on the energy bills per year.

While there is a number of retrospective and hypothetical/experimental studies, only a few studies considering future refurbishment activities can be identified in the existing literature. As examples, the studies of Klöckner and Nayum [27] and Friege [28] can be mentioned. In their study of 3787 Norwegian households, Klöckner and Nayum [27] considered drivers and barriers (in different stages of the decision-making process) referring to planned EERM such as e.g., insulation activities or the replacement of windows. Insulation activities were also regarded in the study of Friege [28] who considered planned refurbishment activities as well as past refurbishment activities in his study among 275 private German homeowners. On the one hand, we want to contribute to the limited understanding of decisions regarding EERM [17] by adding a study using a future-orientated approach in a research field that so far was predominantly analyzed with retrospective and experimental/hypothetical studies. On the other hand, the present study aims to enhance the insights related to the current political activities focused on increasing the refurbishment activities in Germany.

The study is structured as follows: the theoretical and methodological background is outlined in the Sections 2 and 3. Our results related to research target 1 are presented and discussed in Section 4. Finally, we provide conclusions and implications in Section 5 based on our results to meet research target 2.
