## 1 Introduction  
On a global scale, buildings are responsible for more than one-third of the final energy and global CO\({}_{2}\) emissions, and 55% of the total electricity consumption [1]. The 2030 Climate and Energy Amhibition of the European Union (EU) establishes a target of 55% emissions reduction by 2030 compared to 1990 [2]. The building sector is pointed out as having the largest potential for cost-efficient reduction of emissions [2]. An explanation for that can be contributed to the large share of aging and inefficient buildings. It has been reported that residential buildings in the EU account for about 75% of the total building stock, where more than half were built prior to 1960 [3]. It has been estimated that reaching the environmental targets requires 3% of the building stock to be renovated annually [4]. While it is rather complex to measure, study [5] reports annual rates for renovation in the period 2012-2016 to be just 0.2% for deep renovations (above 60% energy use reduction) and 1.1% for medium renovations (between 30 and 60% energy use reduction). To accelerate the process and ensure an increase in renovation rate and depth, the EU Commission has published a renovation wave communication [6]. The objective of the communication is to at least double the annual rate of energy renovation in the EU by 2030 and accelerate deep energy renovations. A number of initiatives are established to speed up the progress and boost the renovation sector across all levels. Communication [6] underlines the need for long-term renovation strategies on a national level to convert existing buildings to nearly Zero Energy Buildings (NZEB). The recast Energy Performance for Buildings Directive (EPBD) defines NZEB as a building with low energy demand that is mainly covered by renewables [7]. The EPBD recast establishes NZEB as a standard for all new public buildings from 2020. The definition remains the same in the latter published Directive 2018/844 [4], which has a strong focus on renovation of existing buildings. While the overall definition is established on the EU level by the aforementioned directives, Member States have the responsibility of defining and implementing national definitions [8]. Reports show that only a few Member States have generated policies for stimulating cost-effective NZEB renovation [9]. Quite extensive research has been carried out in the area of NZEB renovation [10,11]. As the renovation field is quite vast, multiple aspects related to NZEB have been investigated. Definitions and indicators have been reported for specific countries [12] or building types [13, 14, 15, 16]. Studies have also focused on the evaluation of specific solutions for building parts to reach NZEB standard. [PERSON] et al. [17] presents a rooftop extension as a solution; [PERSON] et al. [18] analyze the addition of sun spaces, or rooms to the exterior wall, while variations of facade additions are studied in [19, 20, 21]. In addition to solutions for reaching NZEB, studies have also investigated the gap of expected and achieved energy performance [22]. Possible financial discrepancies that can be caused by occupant behavior are studied in [23], while study [24] investigates the investment gap between cost-optimal and NZEB solutions by macroeconomic scenarios. [PERSON] et al. [11] conducted an extensive literature review of 234 studies, concerning the renovation of multi-family buildings in temperate climate. The authors found that the most occurring strategies for residential renovation consider energy efficiency, whereas other represented topics, such as economic, environmental, architectural, comfort, or risk are also applied to a different extent and depth. The large share of methodologies involving energy and economic factors is partially caused by the well-established cost-optimal approach, incorporating Life Cycle Cost (LCC) calculations.