Evaluating Thermal Insulation Strategies for High-Rise Residential Buildings in Sarajevo

Abstract

Aging residential buildings in urban areas require effective thermal insulation to enhance energy efficiency and indoor comfort. In Bosnia and Herzegovina (BiH), expanded polystyrene (EPS) is the most commonly used insulation material due to its affordability, despite concerns regarding its flammability and environmental impact. While regulatory changes since 2019 have recommended rock wool for high-rise buildings, the absence of binding fire safety regulations has allowed the continued use of EPS, often driven by financial constraints. This study examines energy efficiency refurbishments in Sarajevo’s high-rise residential buildings and analyze the implications of the partial implementation of recommended measures. Using case studies, surveys, and expert interviews, this research identifies key challenges, such as limited funding, fragmented renovations, and inconsistent coordination between stakeholders. The findings indicate that facade insulation is often prioritized over comprehensive upgrades, including window replacement and heating system improvements, leading to suboptimal energy savings and minimal cost reductions for residents. Additionally, the complexity of multi-apartment ownership structures hinders uniform improvements in energy efficiency. Despite these challenges, property values tend to increase after renovation, highlighting the long-term financial benefits. To maximize energy savings and ensure sustainable urban housing, stronger interdisciplinary collaboration, improved funding mechanisms, and adherence to fire-safety standards are necessary. These measures would enhance the effectiveness of renovations and support long-term energy efficiency strategies.

1. Introduction

The global urban population is increasing at a consistent rate, as indicated by a United Nations (UN) study that projects that two-thirds of the world’s population will reside in cities by 2050 [1]. In response to the escalating urban contribution to climate change due to rising greenhouse gas emissions from cities [2], enhancing the energy efficiency of existing building structures may be a viable solution. However, it is important to note that most buildings are only given superficial maintenance, resulting in a lifespan of approximately 50 years [3]. According to strategic data on the construction sector collected by the European Commission, 60% to 85% of new investments are in housing [4]. Housing has a considerable impact on people’s lives, given that they spend the majority of their time in houses or apartments [5]. The thermal insulation of a structure is a key factor influencing its energy expenditure. Consequently, the implementation of thermally insulated walls has been demonstrated to reduce the energy consumption of heating and cooling systems [6].

In the context of Bosnia and Herzegovina (BiH), a confluence of factors has led to a significant shortfall in the quality of the building sector, as evidenced by numerous studies [7]. The prevalence of substandard or non-existent thermal insulation and deteriorating joinery in existing buildings, substandard quality of new constructions, inadequacy or dilapidation of heating systems, and exorbitant costs of natural gas and other “clean” energy sources have contributed to this situation. Furthermore, there has been a notable shift towards the utilization of traditional, less expensive fuels such as coal and wood, which further exacerbates the challenges faced by the sector. In the specific context of school buildings, which play a pivotal role in the social sphere, Katić et al. (2021) [8] elucidated the suboptimal energy performance attributed to the absence of thermal insulation. This conclusion was substantiated by data derived from energy audits of 185 school buildings in BiH. The implications of these findings are extensive, affecting the quality of life of all citizens, both within and beyond the confines of their dwellings. This assertion is corroborated by Korjenic et al. (2023) [9] in a comparative case study of residential building projects in Germany, Croatia, and BiH. The study found that Sarajevo exhibited the lowest livability due to the complete avoidance of sustainable building standards by the authorities in BiH. However, as humanity continues to make advancements in the field of construction, the necessity for shelter and weather protection—particularly the mounting demand for comfort—is driving a progressive increase in the utilization of thermal insulation for buildings to enhance energy efficiency. Nevertheless, the incentives for enhanced energy efficiency in high-rise residential buildings in Sarajevo are limited, as most of them are heated by a centralized district heating company, where the cost to the resident is fixed per square meter of the heated area, regardless of energy consumption.

The primary objective of this study is to assess the effectiveness of thermal refurbishment in three selected high-rise residential buildings in Sarajevo. This investigation will place particular emphasis on the impact of refurbishments on energy efficiency and occupant satisfaction. This study seeks to demonstrate that the implementation of rehabilitation measures that lack strategic direction often falls short of delivering substantial energy savings. The study’s findings, which elucidate the prevalent challenges and deficiencies in renovation practices in BiH, are expected to provide valuable insights for policymakers, investors, and construction companies in BiH, highlighting the extent to which retrofitting measures can enhance the indoor environmental quality and reduce energy consumption. This research is a robust advocacy tool for promoting more responsible and sustainable public investments in energy efficiency. This study underscores the need for the development of more effective action plans and the implementation of improved building stock databases, as there is currently a lack of information about the energy performance of existing buildings and the number of buildings in urgent need of renovation. This study underscores the significance of interdisciplinary collaboration and strategic partnerships in enhancing the efficacy of energy efficiency initiatives. Given the reliance on public funding, a more pronounced commitment from public investors is imperative to ensure the long-term success and sustainability of energy efficiency improvement.

Following the presentation of the study’s methodology, the findings from the three case studies are outlined, followed by a summary of the questionnaire survey results and key insights from the expert interviews. Subsequently, the main conclusions derived from the combined methodological approaches are analyzed, culminating in a discussion of the challenges associated with the energy-efficient retrofitting of high-rise buildings in Sarajevo.

2. Materials and Methods

The methodology of this scientific research work includes a combination of qualitative and quantitative methods. First, case studies of selected buildings were conducted, followed by interviews with experts in the field of energy efficiency (qualitative). In addition, a questionnaire survey was administered to tenants of three selected high-rise residential buildings in Sarajevo to collect quantitative data on their housing satisfaction (quantitative). The buildings in question are located in Phase B of the “Alipašino Polje” settlement, the “Hrasno” settlement, and the “Jezero” settlement, respectively.

The collected and analyzed case study data provided insights into the present conditions of the selected high-rise residential buildings. The survey data were then used to assess the impact of the completed thermal retrofits, as reported in the case studies, on tenants’ housing satisfaction. An in-depth interview was conducted with experts who thoroughly evaluated the valuable information from the case studies and data collected from the residents of the selected high-rise buildings. This comprehensive analysis established a robust correlation between all three segments of this paper. The aforementioned methods provide a stable and proven approach for analyzing the objective of this paper, which is to evaluate the effectiveness of thermal refurbishments using EPS in high-rise residential building complexes in BiH, specifically in Sarajevo.

According to the “Rulebook for Fire Protection of Tall Buildings” in the Canton of Sarajevo, a high-rise building is defined as a building for temporary or permanent residence of people with residential, business, or residential-business character, where the highest floor is at least 22 m above the lowest elevation of the terrain [10]. To investigate thermal retrofitting practices throughout the canton, three case studies of high-rise residential buildings in three different municipalities were selected. The high-rise residential buildings are located in Phase B settlement “Alipašino Polje” (Case Study 1), in the settlement “Hrasno” (Case Study 2), and in the settlement “Jezero” (Case Study 3), all in the urban zone of the City of Sarajevo. The selection of these buildings was driven by their recent participation in a thermal rehabilitation initiative, specifically the implementation of thermal insulation measures within the building envelopes. The geographical locations of the selected high-rise residential buildings are shown in Figure 1, which also illustrates the urban context of the study.

The subsequent steps constitute the case study analysis of the selected buildings.

First, general information about the buildings will be analyzed. This includes the location, year of construction and renovation, number of floors, structural system used, number of apartments, type of heating system, heat billing, and presence of ventilation or cooling systems. Then, geometric parameters will be defined. These include envelope elements, orientation, total area, total envelope area, heated area, heated volume, and compactness ratios. The thermal and energy parameters will also be defined. These include elements and their U-values, energy consumption, and CO₂ emissions of the selected high-rise residential building.

In addition, the following elements will be analyzed:

• thermal rehabilitation practices;
• the thermal renovation of the building envelope (elements, technical renovation solutions, results);
• photos of the state of the building before and after the renovation;
• information on the improvement of existing equipment (heating, cooling, ventilation, domestic hot water, lighting, and renewable energy systems).

The information collected and analyzed from the case studies was used to provide insights into the current structural conditions of high-rise residential buildings. However, it is also important to consider that people live in these selected buildings. To consider this social aspect, a questionnaire survey was conducted, which is predicated on two multi-criteria assessment methods: the Home Quality Mark system and NF Habitat HQE, which is a tool for objectively assessing, comparing, and improving the quality of housing projects in Europe [4]. These two multi-criteria evaluation methods were selected because they consist of different categories that can be used to formulate potential questions for the questionnaire survey. For this research, two categories will be used: The first category is comfort, which includes sound insulation and temperature. The second category is quality of life, which includes indoor air quality, building thermal comfort, and living comfort. It is important to emphasize that these two categories and their subcategories are influenced by the architectural factors. The most common factor is the choice of thermal insulation material. This is why the definition of the factor (influencing the quality of living environment) and its measurement methods are an important task in the process of improving people’s living conditions [11].

The questionnaire survey comprised ten questions, which were answered using a binary scale. The survey was administered to the residents of the selected high-rise residential buildings in both digital and print formats. However, a significant proportion of tenants in the buildings declined to respond to the survey, possibly due to the lingering reluctance to share information that has been prevalent since the Bosnian War (1992–1995). The demographic statistics of the sample of people approached with questionnaires are shown in

Table 1. Questionnaire survey statistics.

	Case Study 1 (CS1)	Case Study 2 (CS2)	Case Study 3 (CS3)
Settlement	Alipašino Polje	Hrasno	Jezero
Location	Novi Grad	Novo Sarajevo	Centar
Residential units	69	162	53
Questionnaires answerd	25	21	8
Response rate	36%	13%	15%

.

Following a thorough analysis of the case studies and completion of the questionnaire survey, an interview was conducted with two individuals from a company that specializes in energy consulting services, with a focus on energy efficiency and renewable energy sources. This particular company was chosen for the interview because it conducted an in-depth energy audit [12,13,14] of the high-rise residential buildings that were studied as part of the research. The valuable information from the case studies and the data collected from the residents of the selected high-rise buildings were thoroughly evaluated by experts through in-depth interviews. This comprehensive analysis resulted in a strong correlation between all three sections of this paper.

3. Results

A dual approach was employed to analyze the collected data, encompassing both qualitative and quantitative methods. This approach yielded valuable insights and conclusions, as discussed in the following sections.

3.1. Case Studies

For the case studies, three high-rise residential buildings located in different municipalities of the city of Sarajevo that have undergone thermal refurbishment in the last 15 years were selected for analysis. All three buildings were constructed over a period of approximately 10 years, with Case Study 3 being the earliest, as shown in

Table 2. General data of the selected high-rise buildings [11,12,13,14,15].

	CS1	CS2	CS3
Floors above ground floor	15	20	12/13 1
Year of construction	1971–1975	1968–1969	1964
Heat supply	District heating 2	District heating 2	District heating 2
Ventilation/cooling system	None 3	None 3	None 3
State Before Renovation	Poor facade condition, mechanical damages	Worn-out facade, poor insulation	Moderate condition, outdated insulation

¹ 13 floors on the east side and 12 floors on the west side. ² CPUC Toplane–Sarajevo. ³ individual air conditioning units installed.

. The buildings included a basement, ground floor, and 12 to 20 standard floors; Case Study 2 was the tallest in terms of the number of floors. The selected high-rise buildings were served by district heating. The relevant general data of the case study buildings are listed in Table 2, and the relevant building geometry parameters are listed in

Table 3. Building geometry parameters of the selected high-rise buildings [11,13,14,15].

	CS1	CS2	CS3
Total envelope area [m2]	4759.89	6958.14	2803.88
Heated area [m2]	4466.19	6847.23	2574.23
Heated volume [m3]	12,742.34	19,598.90	n.d. 1
Compactness ratio [m−1]	0.33	0.36	n.d. 1

¹ not declared.

. Detailed geometric data are presented in Appendix A.

The thermal renovation measures examined in the case studies were analogous: the external walls were retrofitted with an external thermal insulation composite system (ETICS) composed of EPS; the external windows and doors were replaced with PVC windows featuring double insulating glazing; and the flat roofs were insulated with a 10 cm layer of EPS beneath a roofing membrane (CS1) or a new bituminous waterproofing and a 10 cm (CS3) or 20 cm (CS2) layer of extruded polystyrene (XPS) with a gravel top. Following the retrofit measures, resident satisfaction was shown to improve in all three case studies, as evidenced by the results of the questionnaire survey (see Section 3.2). Comprehensive data on the renovations are presented in

Table 4. General data on the renovation of the selected high-rise buildings [12,13,14].

	CS1	CS2	CS3
Year of renovation	2016	2018	2018
Thermal insulation material 1	EPS	EPS	EPS
Thickness of insulation 1	10 cm	10 cm	10 cm
Resident satisfaction	Improved, moderate satisfaction	Improved, high satisfaction	Significantly improved, high satisfaction

¹ of exterior wall.

. Technical drawings illustrating characteristic post-retrofit details are provided in Appendix B.

3.1.1. Case Study 1

The first case study focuses on a high-rise residential building complex in the municipality of Novi Grad, situated in the settlement of “Alipašino Polje”. The facility comprises five high-rise residential buildings in the B phase of the “Alipašino Polje” settlement. One exemplary building was selected for further analyses. The residential units in this building are oriented toward all four sides, and the building has a basement that is partially buried and contains storage rooms. The exterior walls of the basement were not treated with thermal insulation and remained in their original materialization with a new layer of finishing plaster. The calculation of the thermal energy for heating is collective for all apartments, based on the heat meters located in the basement. The consumption of hot and cold water was calculated on an individual basis. The analyzed building was not designed or equipped with a ventilation or cooling system. However, individual apartment owners have installed air conditioning units on their premises, which are visible on the building’s facades [12].

In the course of planning the rehabilitation of the building, the property management established a series of guidelines for the reconstruction and redesign of the facades. During the war, the facades suffered mechanical damage, primarily from the impact of grenades, shrapnel, and bullets. Inadequate maintenance of the damaged facade elements resulted in further deterioration and the loosening of certain components to the extent that these elements posed a hazard to passersby. The primary objective of the reconstruction and redesign initiative was to ensure the safety of individuals and property, addressing the concerns raised by damaged facades. Additionally, property management placed emphasis on enhancing the insulation of the facades to optimize thermal protection and energy efficiency. The redesign of the facades was guided by three overarching principles: aesthetic enhancement, functional justification, and addressing the issue of unplanned balcony closure, installation of air conditioners, antennas, and other fixtures [12].

A visual representation of the transformation of the high-rise building is provided in Figure 2, showcasing a before-and-after comparison of the renovation.

3.1.2. Case Study 2

The edifice selected for Case Study 2 is situated in the “Hrasno” settlement in the municipality of Novo Sarajevo. It is a high-rise residential building with ground floor spaces that are partially utilized as offices, and later adapted service spaces on the flat roof or terrace that were converted into apartments. Following the war, the building’s exterior walls and woodwork sustained significant damage, prompting repairs in 1998. This included the reconstruction of damaged sections of the building shell and the replacement of damaged woodwork. To date, approximately 60% of the original carpentry and lockwork have been replaced, including wood and PVC components.

The high-rise residential building did not have a central cooling system. Consequently, decentralized air-conditioning units were installed on the facade, and hot and cold water consumption was calculated on an individual basis [13].

A study of potential energy efficiency methods, in conjunction with an analysis of the status of the thermal properties of the selected high-rise residential building envelope, resulted in the implementation of the following energy efficiency measures: replacement of the current thermally inefficient carpentry and lockwork, thermal insulation of the building’s exterior walls with EPS, and renovation and upgrading of the building’s flat roofs [16].

A comparison of the building before and after retrofitting is shown in Figure 3.

3.1.3. Case Study 3

The high-rise residential building selected for Case Study 3 is located in the “Jezero” settlement, with ground floor spaces utilized for both commercial and residential purposes, and with the consumption of hot and cold water calculated on an individual basis [14].

Since the last war, only the flat roof above the building has been partially repaired in 2011. The exterior walls of the high-rise residential building are composed of different materials: on the ground floor, on the east and west sides, as well as on the top floor of the building, there are solid brick walls with finishing facade plaster; the parapet walls on the standard floors are solid brick with finishing asbestos-cement boards, and the side facade walls are reinforced concrete walls with finishing coating of asbestos-cement boards. Over the years, approximately 70% of the original exterior carpentry has been replaced by the building’s occupants, while the asbestos-cement board facade has not yet undergone renovation. In 2011, the roof terraces of the building were renovated as part of a comprehensive initiative to renovate the building’s flat roof. This initiative also encompassed the repainting of facades [14]. However, the implementation of thermal insulation measures for the facades was postponed until 2018.

A comparison of the tower’s appearance before and after the last renovation is shown in Figure 4.

3.2. Questionnaire Survey

The design and implementation of the survey presented certain challenges, primarily due to the necessity of coordinating with tenants’ business and personal commitments to complete the survey. Ensuring the receipt of responses from all tenants also proved to be a challenge, as many were absent from their apartments on multiple occasions during the survey period. Another significant factor that contributed to the limited number of responses was that many of the current tenants did not reside in the building prior to the facade renovation. Consequently, their perspectives were deemed irrelevant for evaluating the impact of the facade renovation, as no discernible differences could be observed before and after the renovation. The questionnaire survey comprised a series of questions and ratings, the full list of which is presented in

Table 5. Questions and ratings of the questionnaire survey.

	Question	CS1	CS2	CS3	Results in Total
1	Have you been informed about the reconstruction of the building envelope (installation of thermal insulation and replacement of windows) in your building?	YES: 21 (84%) NO: 4 (16%)	YES: 19 (90.5%) NO: 2 (9.5%)	YES: 6 (75%) NO: 2 (25%)
2	Have you noticed the difference in temperature in your apartment before and after the renovation of the facade envelope?	YES: 24 (96%) NO: 1 (4%)	YES: 20 (95.2%) NO: 1 (4.8%)	YES: 8 (100%) NO: 0 (0%)
3	Have you noticed that the rooms in your apartment stay warm longer after the central heating in the apartment is turned off after the renovation of the buildingʹs facade envelope?	YES: 23 (92%) NO: 2 (8%)	YES: 21 (100%) NO: 0 (0%)	YES: 8 (100%) NO: 0 (0%)
4	Before the renovation of the building envelope, did you have to use additional methods of heating in the apartment apart from the city’s central heating?	YES: 7 (28%) NO: 18 (72%)	YES: 10 (47.6%) NO: 11 (52.4%)	YES: 4 (50%) NO: 4 (50%)
5	After the renovation of the building envelope, did you have to use additional methods of heating in the apartment apart from the city’s central heating?	YES: 1 (4%) NO: 24 (96%)	YES: 3 (14.3%) NO: 18 (85.7%)	YES: 0 (0%) NO: 8 (100%)
6	Have you noticed a difference in the noise coming from the outside into your apartment before and after the renovation of the facade envelope?	YES: 21 (84%) NO: 4 (16%)	YES: 16 (76.2%) NO: 5 (23.8%)	YES: 6 (75%) NO: 2 (25%)
7	Have you noticed the appearance of window fogging or mold on the surface of the walls after the renovation of the facade envelope of the building?	YES: 2 (8%) NO: 23 (92%)	YES: 1 (4.8%) NO: 20 (95.2%)	YES: 0 (0%) NO: 8 (100%)
8	Did you have health problems related to the indoor air quality in the apartment after the renovation of the building envelope?	YES: 0 (0%) NO: 25 (100%)	YES: 1 (4.8%) NO: 20 (95.2%)	YES: 0 (0%) NO: 8 (100%)
9	Are there thermostatic radiator valves installed in your apartment that enable automatic temperature regulation in the room?	YES: 0 (0%) NO: 25 (100%)	YES: 2 (9.5%) NO: 19 (90.5%)	YES: 7 (87.5%) NO: 1 (12.5%)
10	Are you satisfied with the completed works on the reconstruction and insulation of the facade envelope?	YES: 24 (96%) NO: 1 (4%)	YES: 19 (90.5%) NO: 2 (9.5%)	YES: 7 (87.5%) NO: 1 (12.5%)

.

Despite the relatively low response rate of approximately 19% (see also Table 1), the survey responses offer valuable insights. The operational schedule of the communal heating system is from 5:00 a.m. to 10:00 p.m., at the latest [16], regardless of the energy performance of the building. Prior to the renovation, a significant concern was the rapid decline in apartment temperature after deactivating the heating system, which was primarily attributable to inadequate insulation. However, following the renovation, a substantial proportion of respondents (96.3%) attested to a discernible difference in temperature compared to their previous experiences, with an observed increase in the duration of sustained warmth. Facade renovation also reduced reliance on supplementary heating sources beyond the primary system. Moreover, a significant majority of respondents (76.6%) reported a decrease in noise levels in their flats after renovation. Furthermore, a substantial proportion of tenants, 94.4%, reported a decline in the incidence of condensation on windows and mold on walls following the renovation. Only one tenant, constituting 1.8% of the sample, reported health concerns related to indoor air quality. Additionally, it is noteworthy that 83.3% of respondents lacked thermostatic radiator valves, which hindered their capacity to regulate apartment temperature. While the majority of respondents expressed satisfaction with the facade renovation, they also articulated concerns regarding its potential impact on their energy expenditures.

Subsequent to the inquiry regarding the respondents’ affirmative or negative responses, an additional question was posed, inviting tenants to offer their feedback on the energy efficiency of the building, quality of the workmanship, and their overall satisfaction following the facade renovation. The specific inquiry posed was as follows: “Do you have any comments on the project and the works that were carried out during the renovation of the facade envelope?” The predominant interest of the tenants pertained to their heating expenditures, as they anticipated that the renovation of the envelope would result in substantial savings and enhancements to the ambient temperature of their residences. In fact, the majority of residents expressed satisfaction with the temperature achieved, even during the colder winter months.

A notable phenomenon that has been observed is that a considerable number of tenants routinely ventilate their living spaces and leave specific windows open, asserting that the ambient temperature is higher than necessary. Concurrently, the tenants continued to pay the same amount for heating. Consequently, some tenants have inquired about the possibility of reducing heating bills, given the significantly improved energy efficiency in terms of energy consumption.

3.3. Interview

The interview was conducted with two individuals from a company specializing in energy consulting services with a focus on energy efficiency and renewable energy sources. One individual is identified as a “Project Manager”, while the other individual holds the position of “Project Management/Laboratory Manager”. The rationale for selecting this particular company for the interview is that it conducted an in-depth energy audit of the high-rise residential building facilities that were studied as part of the research. The objective of the interview was to gain insight into the experts’ perspectives and experiences, as well as the issues that arose during the energy audits they performed. A transcript of the interview is provided in Appendix C.

The subjects deemed to be of particular relevance are as follows: the selection of buildings for renovation; the financing of renovation works; the most commonly used types of thermal insulation materials for high-rise buildings in theory and practice; the proposed energy efficiency measures within the selected buildings; the challenges or obstacles in the process of implementing energy efficiency measures; measures related to the EU Directive for Nearly Zero Energy Buildings; impressions after renovation; and the audit process.

The experts elucidated that an endeavor was undertaken to renovate four high-rise residential buildings in the “Hrasno” settlement, with the municipality committing to finance approximately 80% of the costs and the tenants responsible for the remaining 20%. However, only in one of the four high-rise buildings did the tenants successfully raise the necessary funds. The municipality frequently issues similar public appeal.

The process of renovating the building envelope and improving the building’s energy efficiency typically commences with an energy audit prior to the main project. However, experts emphasize that the main project may or may not adhere to the recommendations outlined in the energy audit. For instance, an energy audit may recommend the installation of 10 or 15 cm of facade insulation; however, the primary project may opt for an 8-cm alternative. Additionally, the audit may suggest replacing existing windows with aluminum or wooden windows, but the primary project may select PVC windows to reduce costs. This dynamic also applies to the type of insulation that is recommended. For instance, an energy audit may suggest rock wool insulation, which is frequently substituted with EPS insulation. This discrepancy may be attributed to the fact that the audit and the primary project are not carried out by the same company.

A further challenge arises when the individual tasked with preparing the audit and proposing measures, such as facade renovation and window replacement, also suggests modifying the thermal heating system. This is because optimizing the building envelope reduces the need for heating. Despite the emphasis on the interdependence of these two areas, owners and facility managers often have limited resources, which makes it difficult to implement all of the proposed measures. However, the implementation of a limited number of measures identified in the energy audit will not yield optimal results. While the implementation of these measures requires financial investment, various sources of co-financing and public calls are available. However, property owners often decline these opportunities, aware that they will incur similar expenses on utility bills regardless of any investments made in renovations. The reasons for this illogical situation are the lack of thermostatic radiator valves or other technical means to regulate heating and fixed prices for district heating per square meter of heated area, regardless of the energy efficiency of the building. While tenants who have upgraded their building’s energy efficiency may have increased the value of their property, this alone is insufficient to motivate others, given the challenges posed by older buildings with two-pipe heating systems, which are more difficult to upgrade and install. Administrators and owners should consider these findings.

The experts recommend nearly zero-energy building measures for special customers, but they have not received any requests for detailed energy audits. However, the energy certificates indicate that none of the buildings are nearly zero-energy buildings. Furthermore, the energy audits are not followed up with consultation requests from the interviewed experts, and the project is conducted independently, with the subjects uninformed about the process and outcomes. The supervision of the implemented measures is conducted by the project manager, who is not the auditor, highlighting the lack of continuity and oversight in the projects.

3.4. Combined Analysis

A dual approach was employed to analyze the collected data, encompassing both qualitative and quantitative methods. This approach yielded valuable insights and conclusions, as discussed in the ensuing paragraphs.

First, a case study was conducted, revealing that from 2016 to 2018, the external facades of high-rise buildings in Sarajevo were predominantly insulated with 10-cm-thick EPS. However, a subsequent analysis revealed a substantial reduction in the heat transfer coefficients (U-values) of the external walls, flat roofs, windows, and doors after the renovation of three high-rise residential buildings. For the flat roof in Case Study 1 and the floor slab above the basement, the post-retrofit U-values remained constant due to the absence of thermal retrofit measures. As the U-values after renovation did not reach the limits of the proposed maximum U-values, as shown in

Table 6. U-values in [W/m²K] of the main building components of the selected high-rise buildings before and after refurbishment, compared with the suggested values [12,13,14].

Element	Suggested U-Values [17]	CS1		CS2		CS3
		Before	After	Before	After	Before	After
Exterior walls	<0.18	0.84	0.27	1.34	0.34	1.93	0.23
Flat roof	<0.13	0.35	0.35	0.53	0.12	0.69	0.35
Windows and doors	<1.40	3.20	1.40	2.50	1.40	2.55	1.40
Floor over unheated basement	<0.13	0.79	0.79	1.89	1.89	2.82	2.82

, the findings underscore the prevalence of unsustainable practices throughout the canton.

It is imperative to underscore that the thermal energy calculation of each high-rise building is collective for all apartments. A comparison of the average temperature for the winter months from

Table 7. Average temperatures during the winter months in Sarajevo [18].

Average Temperature for Winter Months in °C
	Jan.	Feb.	Mar.	Nov.	Dec.	Average	Annual Average
2014	5.0	7.8	8.1	8.9	2.7	6.5	10.01
2015	0.9	1.7	5.3	6.0	−0.5	2.7	10.8
2016	1.2	7.4	6.1	6.1	−0.9	4.0	10.9
2017	−4.8	5.2	8.5	4.9	2.1	3.2	11.0
2018	4.1	0.6	5.4	7.6	0.5	3.6	10.5
2019	−1.5	2.5	7.7	10.6	3.1	4.5	11.7
2020	−0.6	5.0	6.5	5.3	4.5	4.1	11.2
2021	1.3	5.0	4.6	7.0	2.5	4.1	11.2
2022	−0.7	3.9	4.4	7.4	5.3	4.1	11.8

with the amount of energy consumed by the high-rise residential buildings 2 years before and 2 years after the renovation (see

Table 8. Energy consumption and average temperatures for the case studies [19].

Years	Consumption in kWh/m2a			Average Temperatures in °C
	CS1	CS2	CS3	CS1 1	CS2 2	CS3 2
2 years before renovation	100.6	121.1	204.6	6.5	4.0	4.0
1 years before renovation	120.8	125.4	220.4	2.7	3.2	3.2
1 years after renovation	102.5	96.4	182.5	3.2	4.5	4.5
2 years after renovation	121.2	97.3	181.9	3.6	4.1	4.1
Average change (before/after renovation)	+1%	−21%	−14%	−1.2	+0.7	+0.7

¹ Renovation in 2016. ² Renovation in 2018.

) reveals a proportional relationship between the average temperature and the energy consumption of the buildings. Consequently, the observed energy consumption reductions of 21% for Case Study 2 and 14% for Case Study 3 cannot be attributed exclusively to the renovation; rather, they are likely attributable to the varying intensity of the winter months during the specified years. In Case Study 1, no significant change in energy consumption was detected after the renovation.

A secondary conclusion that emerged from the questionnaire survey is that the general consensus of residents regarding the renovation of the building facade and the improvement of thermal comfort in the residences is that, in the post-renovation period, the indoor air temperature has increased to a point that is warmer than necessary during the winter months. Concurrently, residents have not observed a decrease in their heating expenses as the heating system remained unchanged following the renovation, lacking any regulatory capability by the residents. It is noteworthy that thermostatic radiator valves, a pivotal component of the energy audit, were not installed in the apartments. This oversight has led to substantial energy expenditure, as many respondents have had to resort to opening windows when temperatures are excessively high, as they lack alternative means to reduce the indoor temperature.

In accordance with the “Rules for Fire Protection of Tall Buildings” in the Canton of Sarajevo, the facade of a building must be composed of materials that do not facilitate the transmission of fire from one floor to another. The minimum distance between openings on two adjacent floors on the facade was stipulated as 1 m. In instances where this distance is less than 1 m, the flame path between the floors must be extended by installing cantilevered parts of the building structure at the level of each floor [10]. For the thermal insulation of CS1, EPS was used for all four facades, with rock wool fire barriers positioned 20 cm above the windows and 20 cm from the edge of the openings. However, the break distance between openings on two adjacent floors was less than 1 m, thereby failing to meet the minimum requirement for fire safety. It is also noteworthy that the code stipulates materials that are incapable of transmitting fire from one floor to another. EPS is a material classified as flammable. Consequently, its utilization in the facades of high-rise buildings is in conflict with the “Rules for Fire Protection of Tall Buildings” in the Canton of Sarajevo.

Finally, the expert interview underscored the considerable potential for energy consumption reduction through the comprehensive implementation of the measures enumerated in the audit. These measures encompass, among other aspects, the enhancement of thermal insulation for external building components and adaptation of the heating system. In the case studies examined, the implementation of all measures proposed in the energy audits was constrained by budgetary limitations. The execution of these measures, to the extent that they were implemented, did not result in the anticipated energy savings for residents. Consequently, these high-rise residential buildings have merely been endowed with a new facade and excess heating.

4. Discussion

The renovation of high-rise residential buildings in Sarajevo is primarily financed through a combination of municipal co-financing and citizen contributions. Despite the existence of public funding programs, financial constraints often necessitate the selection of the most cost-effective solutions, such as the extensive use of expanded polystyrene (EPS) for insulation. However, regulatory changes since 2019 have recommended the use of rock wool for taller buildings due to its improved fire resistance. Nevertheless, the use of EPS remains prevalent due to the absence of legally binding fire resistance regulations.

A significant challenge in implementing comprehensive energy-efficient renovations is the partial implementation of the recommended measures. Energy audits propose a comprehensive set of interventions, including facade insulation, window replacement, and heating system upgrades, to achieve significant energy savings. However, financial constraints often result in the selective implementation of these measures, where only facade improvements are carried out. This fragmented approach diminishes the overall effectiveness of renovations, as heating demand reductions are not realized when there is no temperature regulation, leading to minimal cost savings for the residents. Consequently, while buildings may appear aesthetically improved, they may fail to achieve the anticipated energy efficiency benefits.

This issue is further complicated by the diverse ownership structures characteristic of multi-apartment buildings. In contrast to public institutions, where a centralized authority can enforce systematic renovations, privately owned residential buildings face logistical and technical challenges. The heterogeneity of individual apartment modifications, including variations in radiator installation and enclosed balconies, hinders the implementation of uniform energy efficiency measures. Moreover, some tenants expressed satisfaction with indoor temperatures prior to the renovations, underscoring that their primary concern pertained to heating costs rather than thermal comfort. Consequently, the implementation of a multifaceted strategy is imperative to incentivize energy efficiency measures in individual apartments. This multifaceted strategy should entail two components: the installation of temperature regulation and meters of energy use and the implementation of a fee-based energy usage charge. The latter should be calculated on a per-unit basis, regardless of the heated area of an apartment.

Despite the aforementioned challenges, energy efficiency renovations have been demonstrated to yield long-term financial and qualitative benefits, as indicated by Dedović et al. (2020, 2024) [20,21]. These studies propose the use of photovoltaic systems for heating buildings in order to ensure clean air and reduce energy poverty in BiH. In addition, property values have been shown to increase following renovations, with improved insulation and window replacements contributing to higher market demand, which was analyzed by Österbring et al. (2019) [22] on a building portfolio scale. However, the fragmented implementation of energy audits and renovation projects, often managed by disparate entities, can result in inconsistencies in material selection and technical execution. Furthermore, instances in which construction commences exclusively based on energy audit recommendations, devoid of a comprehensive main project, underscore the necessity for a more systematic approach to ensure optimal outcomes.

As emphasized by Klaric et al. (2019) [23], state support for formal and non-formal education at all levels is essential for fostering interdisciplinary collaboration among key stakeholders, including policymakers, industry representatives, and academic institutions. The implementation of such initiatives would facilitate knowledge transfer, innovation, and long-term strategic planning in the housing sector. Increased public awareness, streamlined funding mechanisms, and mandatory adherence to holistic renovation strategies can significantly improve energy efficiency outcomes. Furthermore, the establishment of robust public-private partnerships, in conjunction with adherence to fire safety standards, is anticipated to generate more sustainable and resilient urban housing solutions. Government-backed incentives, such as tax exemptions and subsidies, in conjunction with targeted funding for research and education, have the potential to expedite the adoption of sustainable construction methods. The establishment of a national climate database would facilitate the optimization of building solutions based on reliable, long-term meteorological data.

5. Conclusions

This study examined the energy and environmental effectiveness of the thermal renovation of high-rise residential buildings in Sarajevo, the capital of Bosnia and Herzegovina. A questionnaire survey was administered to residents to assess their quality of life after the renovations, which were subject to three case studies. The results of the survey and case studies were discussed in an expert interview.

A significant proportion of the survey respondents reported an improvement in indoor temperature stability after the facade renovation, underscoring the effectiveness of thermal insulation. Many occupants expressed satisfaction with the indoor temperatures achieved even during the colder months. However, the full potential for energy savings was not realized due to the inadequate implementation of the experts’ recommendations. For example, thermostatic radiator valves to reduce heating were not installed in all the apartments. As a result, the building’s energy consumption was reduced by only 14% and 21% for the CS3 and CS2 buildings, respectively. In the case of CS1, the energy consumption did not change significantly after the renovation. This unsystematic and fragmented implementation of retrofit measures is bound to lead to disappointment among occupants, as the expected energy cost reductions do not materialize. In fact, the residents of the three case study buildings pay the same amount of heating bills after the renovation as before, because the heating costs for central district heating are calculated at a fixed value per square meter of living space, regardless of the actual consumption.

Achieving substantial energy savings in high-rise buildings necessitates effective design, meticulous implementation, occupant acceptance, and strict adherence to expert recommendations. On a global scale, the utilization of EPS, predominantly for insulation purposes, is pervasive in the construction industry, particularly in roofs, walls, and foundations. However, the flammability of EPS poses a significant concern, especially in high-rise buildings. While legislation in the Canton of Sarajevo [10] and other urban centers globally mandates the utilization of non-combustible materials for building facades, these regulations are not consistently enforced in practice.

To foster a more sustainable and cost-effective future, it is imperative to implement mandatory monitoring and data collection for all energy efficiency projects, a practice that is currently absent in the Federation of Bosnia and Herzegovina. Future research should prioritize the analysis of price, quality, and selection of different thermal insulation materials to provide more sustainable solutions for future applications in high-rise residential buildings.