Examining Energy Efficiency and Retrofit in Historic Buildings in the UK

Abstract

The energy efficiency potential of a considerable number of Europe’s historical buildings is noteworthy. However, policymakers often express concerns about energy retrofits that may compromise the integrity of these structures and their surroundings. On the contrary, various strategies exist for enhancing energy efficiency in historic buildings without compromising their architectural constraints. The main aim of this study is to examine energy efficiency and retrofit strategies for historic commercial buildings in the UK. The case study that was selected is a historical building constructed in 1865 for the Water Works Company in the UK, whose function has changed through the years. The research methodology employed a combination of techniques that incorporated literature reviews, a case study, semi-structured interviews, and dynamic thermal simulations. For the purpose of obtaining reductions in emissions of greenhouse gases and consumption of energy, the energy performance of five different retrofit treatment methods that have the smallest damaging effect on historical significance was examined. This study demonstrates the effectiveness of integrating advanced building performance strategies, including wall enhancements, the optimisation of HVAC systems, and the implementation of minimally intrusive photovoltaic solutions. These interventions collectively contributed to achieving remarkable reductions in energy consumption, with electricity usage reduced by 100% and natural gas consumption decreased by 88.2%. Applying retrofit strategies reduced CO₂ emissions by approximately 95% from 20,493.51 kg to 1274.76 kg per year. The findings underscore that, despite the considerable potential for enhancing energy efficiency in historic structures, there exists an extensive absence of understanding among homeowners concerning accessible regulations, grants, and practical energy-saving measures.

1. Introduction

A sharp rise in carbon dioxide released prompted action from every country. In total, 195 countries came to a consensus in Paris in 2015 to reduce their emissions in an effort to reduce this rise in global temperatures [1]. The European Commission has put forward a proposal to reduce net greenhouse gas emissions by a minimum of 55% by the year 2030, relative to the levels recorded in 1990 [2].

The building sector, accounting for approximately 40% of worldwide energy consumption, plays a significant role in global energy usage. Primarily reliant on non-renewable sources, this sector also contributes up to 30% of annual greenhouse gas (GHG) emissions on a global scale [3]. The building stock in Europe is responsible for around 40% of the overall energy consumption in Europe, as stated by the European Commission in 2020 [4]. Of the total number of homes, 20% were constructed prior to 1919, while 24% were built after 1980 in the UK [5].

To address the issues imposed by climate change and reduce reliance on fossil fuels, it is crucial to investigate potential avenues for decreasing energy consumption and enhancing the energy efficiency of the current building inventory through the implementation of retrofitting methods and strategies [6]. Thus, finding solutions for these buildings that are consistent with conservation can play a major role in helping the EU achieve its goals for lowering CO₂ emissions [7].

A pertinent inquiry arises regarding the attainable level of energy performance that can be targeted for historic buildings. Presently, building regulations emphasise achieving near-zero energy consumption for newly constructed and refurbished buildings. However, it is important to acknowledge that this ambitious objective may not be feasible for numerous historic buildings, although exceptions do exist [8].

To address climate change, it is crucial to minimise its impact by enhancing the energy efficiency of current buildings [9]. Among these buildings, historic and cultural heritage structures require special attention. Additionally, Webb [10] argues that energy retrofits can lower building energy use and carbon emissions; nevertheless, they present difficulties when applied to historically significant and conventionally built structures. Moreover, Mazzarella [11] states that the most interventions encompass regulations that are inadequate, despite historic buildings meeting all energy-saving objectives. Their preservation and restoration necessitate meticulous planning, and improving their energy efficiency often presents significant challenges [10].

Lidelöw et al. [12] implemented an extensive review of energy-saving techniques for heritage buildings, reaffirming the complexity associated with this endeavour. To support the sustainable development goals outlined in Vision 2030, it is imperative to enhance the energy and environmental performance of existing historical structures [13]. This objective can be accomplished not only by reducing energy demand but also by integrating efficient technologies into these buildings. As an initial step, it is essential to assess the actual energy usage of historical buildings; however, there have been limited comprehensive studies on energy conservation measures in historical buildings in the United Kingdom. Hence, the purpose of this research is to contribute to the existing literature by identifying the factors contributing to high energy consumption in historic buildings and proposing viable and suitable solutions that uphold their architectural significance in accordance with current policies.

The lack of understanding of the current regulations for retrofitting historic buildings is a problem for homeowners, professionals, and local authorities [7]. Despite many directives and guidelines, conflict between energy strategies and architectural value continues. Energy improvements may decrease building energy use and carbon emissions, but they present difficulties when applied to historically significant and conventionally built structures [10]. Therefore, the following specific objectives can be identified:

• Analyse the impact of energy retrofits of the historic buildings on energy consumption;
• Identify the challenges the homeowners, architects, and professionals face during retrofitting;
• Outline the guidelines of intervention strategies for enhancing energy efficiency in historic buildings.

An existing Victorian building in the UK is examined with its current state. DesignBuilder software v7 is used to conduct modelling and simulations of the historic building [14]. Semi-structured interviews are designed to understand the challenges that the architects and homeowners faced. Findings from the literature review contribute to proposing the suitable improvements to enhance the energy efficiency in historic buildings. Improvements are also evaluated to indicate the impact of reducing CO₂ emissions and energy consumption. Finally, a comparable table is presented, which provides an outline of the guideline for retrofit strategies in historic buildings.

2. Context and Background Knowledge

This study conducts a comprehensive literature review on two main research themes: policy and energy efficiency. By analysing various works, approaches, and conclusions of different authors, this research delves into the topic and sheds light on any existing research gaps and presents both conflicting and equivalent perspectives. From worldwide legislation to local policies, the UK government and energy efficiency strategies that can be applied to historic buildings during retrofitting are given, examined, and discussed. Different authors’ studies are analysed according to energy performance and the best solutions for every intervention. Implementation processes and challenges for renewable strategies, HVAC systems, glazing, and insulation are given.

2.1. Policy Framework for Energy Efficiency in Historic Buildings

The only regulation regarding architectural heritage worldwide is the World Heritage Convention [15], which was approved by 190 countries in 1972. After 13 years, the Granada Convention, which was formulated by the Council of Europe, was signed by 46 countries in 1985. The primary objective of the convention is to strengthen and advocate for policies aimed at preserving and improving Europe’s heritage [1].

European Union directives Directive 2002/91/EC [16] and 2010/31/EU [17] aimed to reduce consumption of energy, which became 40% of the overall energy usage in the Union (EUR-lex). Eight years after Directive 2002/91/EC, the EU established a new directive in 2010 named Directive 2010/31/EU, which stated that “in order to achieve cost-optimal levels, member states must take the necessary steps to ensure that minimum energy performance requirements are set for building elements that are a part of the building envelope and that significantly affect the building envelope’s energy performance when they are replaced or retrofitted”. However, it mentions that member nations may exempt certain buildings from energy performance requirements, including the following:

• Protected Buildings: Buildings of architectural or historical significance where compliance would alter their character.
• Religious Buildings: Structures used for worship and similar purposes.

Directive (EU) 2018/844, as an amendment of Directive 2010/31/EU, states that every member state must develop a comprehensive plan for renovating residential and non-residential buildings, including public and private ones, to make them extremely energy-effective and low in carbon emissions by 2050. This plan should make it easier and more affordable to convert existing structures to almost zero-energy buildings [18]. The effective use of energy is not included in the legislation on the preservation of architectural heritage, and neither are the regulations based on European standards mentioning the energy efficiency of historic structures.

In 2017, the EN presented EN 16883:2017 [19] Conservation of Cultural Heritage: Guidelines for Improving the Energy Performance of Historic Buildings [2]. The objective of the standard is to simplify the process of making decisions about how to combine energy performance, usage, and the preservation of history. To provide a clearer explanation of the frameworks suggested by the existing law, a guidebook has been created. First, ‘Task 59: Comprehensive historic building repair’, aimed at reducing energy consumption and CO₂ emissions (nZEB), assembled a total of 25 organisations from 13 different nations as a part of the Solar Heating and Cooling Program [20]. Such organisations comprise private and public research institutions, authorities on cultural heritage, government departments, and industry [20]. Daniel Herrera-Avellanosa et al. [7] believe that IEA-SHC Task 59 is helpful to implement EN 16883-2017. However, decision-makers should change or improve the directive according to social, financial, and technological challenges [20].

In the United Kingdom, Historic England provides a rational process for deciding on and providing direction about every facet of the historic environment, as well as for balancing its preservation with the requirements and goals of the local populace in terms of the economy and society with The Conservation Principles, Policies, and Guidance [21]. The Planning (Listed Buildings and Conservation Areas) Act 1990 is a UK Parliament Act that changed the rules governing the issuance of planning approval for construction projects, particularly those pertaining to the protected structure process in England and Wales. The statutory considerations of the Act 1990 must be taken into account in any decisions that involve listed buildings, their settings, and conservation areas. Additionally, the relevant policies in the development plan and the National Planning Policy Framework [22] must be observed.

Local planning has an important role in deciding the strategies according to the current policy, which outlines that local planning authorities must consider several factors when they examine the application, including the following:

• Firstly, they should prioritise the preservation and improvement of heritage assets, ensuring that they are utilised in a way that aligns with their conservation.
• Secondly, they ought to acknowledge the benefits that heritage asset conservation may offer to thriving communities, particularly to their financial stability.
• Lastly, they should also consider the importance of new developments in contributing positively to an area’s uniqueness and local character.

According to Mazzarella [11], the objective is to determine cost-effective methods for renovating buildings based on their kind and climate zone. This includes examining significant trigger points, if appropriate, during the structure’s lifespan. In addition, it should include strategies and initiatives to promote affordable and efficient renovation of buildings, such as phased rehabilitation and the implementation of an incentive programme for building renovation permits. It does not underline the retrofitting measurements and guidelines. The techniques and methods to be applied to make historical buildings energy efficient have not been explained. There is not the slightest statement on how the energy retrofit will be carried out while preserving its values and properties.

Historic England’s 2018 guidance for improving energy efficiency in historic buildings emphasises a “whole building approach”, a rational energy planning process. The guide outlines key phases, highlights potential issues, and provides solutions, resources, and practical checklists. It stresses understanding the structure and its context, focusing on four elements: location and position, materials, tools and services, and occupants [23]. Historic England states the subsequent overarching concepts that are applicable to the restoration of historical structures. While creating energy efficiency upgrades, the following should also be considered [24]:

• Use-proven processes and materials compatible with original construction; substitutes must have equivalent technical and aesthetic qualities if originals are unavailable.
• Prioritise extending the lifespan of significant architectural elements while preserving historical integrity.
• Ensure interventions are technically feasible, reversible, or modifiable to allow for future actions.
• Document all tasks thoroughly, ensuring accessibility for future custodians.
• Changes must support or at least not compromise the long-term sustainability of maintenance and repair.

Bertolin and Loli [25] state that one of the main issues that should be considered is to develop a comprehensive method that considers several factors, such as cultural, historic, aesthetic, social, and economic values, while determining the most suitable “green conservative intervention” for a historic structure. In reference to Part L of the Building Regulations, structures that are listed on the register or located in preservation zones are not required to meet energy efficiency standards unless this would severely change the building’s appearance or identity. Part L 0.14, under Historic and Traditional Buildings, states that the energy efficiency of historic and traditional buildings ought to be enhanced solely if it does not result in the long-term degradation of the building’s structure or fixtures. This is especially relevant for historic and traditional buildings constructed with a vapour-permeable design that both absorbs and facilitates the evaporation of moisture [26]. So, assessing the historic building retrofit strategies depends on the building itself.

Most historic buildings are protected by unique national or municipal laws [11]. No repairs may be made to them without specific authorisation from the city’s planning authority, which frequently informs the relevant central government cultural heritage [27]. However, successfully implemented retrofit solutions in historic structures are always the consequence of multidisciplinary decision-making encompassing a range of stakeholders with varying degrees of expertise and a set of objectives [8]. Regulations and procedures related to energy efficiency in old structures may benefit from an interdisciplinary perspective that analyses principles, regulations, and practice [28].

Renovating existing buildings and buildings with historic or architectural value will play a major role in helping to fulfil both short- and medium-term environmental goals, according to Fufa and Flyen [29]. Furthermore, Gings and Painter [30] highlighted that to maintain historic buildings’ historical significance, it is extremely important that their energy efficiency be improved, which is essential for the reduction in emissions. Similarly, Cinieri and Garzulino [31] are concerned with the lack of set criteria for the organisation and management of these programmes, while also considering the extensive influence that these incentives would have throughout Italy. To promote future investments, Arias, Vieites, and Vassileva [27] add that stricter norms and policies must be created, and national and regional governments must work more effectively. The UK government took action to tackle climate change. The government is allocating GBP 12 billion to Help to Heat initiatives to ensure houses are more energy-efficient and cost-effective to heat [32]. These are the Boiler Upgrade Scheme, Home Upgrade Grant Phase 2, Sustainable Warmth Competition, Social Housing Decarbonisation Fund Energy Company Obligation, and Great British Insulation Scheme.

The Framework [26] mandates that local planning authorities give considerable weight to the requirement of promoting energy efficiency and low-carbon heating modifications to existing structures. This gives local planning authorities more information to consider when evaluating applications for planning permission (and listed building consent, where applicable) for energy efficiency improvements. It also protects conservation areas, listed buildings, and energy efficiency while balancing climate change mitigation [26]. In addition, a review published in 2024 by the UK government stated the current situations and challenges about policy gaps that stakeholders and occupants face, as outlined in the following statement: “The National Planning Policy Framework, which outlines the government’s financial, ecological, and community planning strategies for England, had no mention of climate change, which alarmed some stakeholders as well. This meant that when weighing the potential effects on heritage, planners and conservation officials might ignore the merits of carbon-saving strategies. The managers of some conventional buildings also said that it was challenging for them to apply energy-saving improvements throughout their portfolios, as the local planning department had different opinions about what constituted a suitable application, and applications were reviewed in individual circumstances” [33].

The review’s findings confirm the following points:

• There is confusion in the public’s mind about the type of approval, if any, needed.
• There are inconsistencies between local planning authorities.
• The processes can be too slow and uncertain.

The guidance shows that the government admits all these challenges and uncertainties and acted accordingly. In summary, policy is vital to the process of retrofitting historic buildings. Legislation should be clear and understandable for every situation. International agreements, EU directives, and national policies are considered during retrofitting historic buildings. In addition, local authorities are responsible for applying legislation and deciding on each application.

2.2. Energy Efficiency Strategies for Historic Buildings

In this section, energy efficiency strategies that can be applied to historic buildings during retrofitting are discussed. Different authors’ studies are analysed according to energy performance and the best solutions for every intervention. The literature review is continued under four subheadings for energy efficiency: insulation, glazing, HVAC systems, and renewable strategies.

• Insulation

Historic England [23] describes that re-rendering a brick wall in a suitable material as part of a solid wall insulation project, for instance, might be seen as an improvement if the wall has lost its original finish. Energy efficiency improvements may provide a chance to increase a building’s importance through related projects that might not have been carried out otherwise [23].

Li and Tingley [34] believe that the pre-1919 Victorian housing stock’s solid wall insulation has significant potential to lower carbon emissions, and it should be considered a crucial element in helping the UK accomplish its target of reaching net zero greenhouse gas emissions by 2050 [34]. Ji, Lee, and Swan highlight the critical role of fabric enhancement in improving energy efficiency, demonstrating that both external and internal insulation are consistent with policy frameworks [35].

Goksal Ozbalta et al. [36] state that interventions made on the building façade indicate that the 3 cm thick interior insulation on the exterior wall contributed to a drop in the heating demand of 23.95%, the cooling demands of 1.68%, and the overall energy consumption of 2.65% in a historic building in Turkey. They state that the combination of 6 cm thick wall insulation, 8 cm thick basement ceiling insulation, and secondary window application reduced the heating load by 57.82%, the cooling load by 14.45%, and the overall energy consumption by 8.53%.

Annibaldi et al. [37] state that selecting exterior insulation reduces temperature swings, prolongs the duration of the greatest interior surface temperature, and lessens the chance of condensation. However, as this approach requires a substantial modification of the building’s external façade, it cannot be applied when the intervention involves a valuable façade with little potential for transformation [2]. When exterior limitations, for example, structures, decorative elements, and cantons, exist and the interior working temperature may be promptly attained, masonry wall internal insulation is useful [37]. In addition, the loss of floor area—a factor that should not be neglected in historic structures, which are often characterised by tiny rooms and the inability to remove thermal bridges at the junction of the wall and ceiling—represents one of the drawbacks of this alternative. Conventional structures with solid walls are meant to collect and release moisture from the inside as well as the outside [38].

Posani et al. [39] state that thermal mortars emerged as a very practical and possibly successful alternative for aged walls. Insulation of solid walls of historic buildings cannot be applied externally according to existing regulations [23]. On the other hand, heritage building ceilings can be successfully insulated by considering the unique circumstances, particularly regarding the risk of condensation [23]. It may be feasible to incorporate additional insulation based on the floor and foundation structure. An experiment conducted in a historic building demonstrated that by introducing an 80 mm fibreboard, the U-value of the floor decreased significantly from 2.4 W/m²K to 0.7 W/m²K [40].

• Window Replacement

Historic England explains that windows are a significant part of the building [41]. The first step in considering alterations to historic windows is determining the significance of these elements according to the following factors:

• The shape, composition, and background of the windows.
• The windows’ significance.
• The effects of suggested modifications.

Replacing single panes with contemporary slim double glazing can reduce heat loss by 35–73% and improve the U-value by about 60%, but may require adjustments to window frames and removal of historic glass and could slightly decrease natural light [42]. The replacement of windows and the insulation resulted in the largest energy savings [43]. The installation of shutters made from wood on windows with single glazing in historic structures in Scotland, which was conducted by Currie et al. [44], resulted in a significant decrease in the U-value, dropping from 5.2 W/m²K to 1.1 W/m²K. This reduction amounts to a substantial 79% decrease in heat transfer through the windows [44].

• Renewable Strategies: HVAC System

Many studies investigate the practicality of different approaches that adhere to legal constraints to enhance the energy efficiency of the historic buildings that are currently in place. Galatioto et al. [45] assert that while integrating RESs (renewable energy sources) and TESs (thermal energy sources) is difficult, the most crucial tasks involve improving the HVAC/DHW systems and the building envelope’s insulation [45]. Nonetheless, thermal hot water storage systems and solar energy systems were employed in tandem to satisfy the energy and hot water heating demands of a student housing in Vienna. Without altering the façade, the building’s historical significance was maintained, but its overall energy consumption dropped by 78.2%, from 248.9 kWh/m² per year to 54.3 kWh/m² per year [45]. However, Elnegar, Munde, and Lemort [46] pointed out that some constraints had to be taken into account while constructing the PV system because the preservation of the historical importance of historic buildings is the top concern. For instance, the accessible hidden area of the PV system modules had a surface area of 264 m². Furthermore, the PV array’s tilt direction was intentionally concealed from view for those approaching the pavilion. Again, the location of PVs was noted by Battista et al. [47]. The solar panels were arranged in a pitched shape with a 10-degree slant to minimise visual disruption from structures taller than the ancient structure. In total, 468 square meters of PV was installed overall, and the maximum power was 78.4 kW.

Geothermal and photovoltaic systems are examples of sustainable energy sources that should be accepted as developments [40]. Based on the findings from a modelling of a mediaeval Italian building, replacing a gas boiler with a ground-source heat pump system (GSHP) results in an annual reduction in CO₂ equivalent to 3032 kg CO₂ [48]. Similarly, Massarotti et al. reported that a historic building’s architectural and cultural elements, which are conserved by corresponding government bodies, can be enhanced using geothermal heat pumps [49]. According to a case study conducted in Croatia, Cadelano et al. [50] reported that the optimal approach for energy efficiency is to combine ground-source heat pump technology with corrective energy management techniques. This approach led to a 66% decrease in energy expenses when compared to baseline circumstances. In addition, according to a simulation study conducted in an Italian university building by Pisello [51], it was found that replacing the current energy system with a ground-source heat pump, along with water storage tanks installed underground, resulted in a remarkable decrease of 64% for heating and 69% for cooling purposes [51]. Furthermore, Schibuola et al. [52] state that the implementation of these solutions does not give rise to any concerns related to the preservation orders.

3. Methodology

The primary focus of this study is to analyse the impact of energy retrofits in historic buildings to reduce CO₂ emissions. A literature review showed that there is a gap in understanding and applying policies. Improvements that can be performed are not clear enough. The goal is to understand the challenges that both residents and professionals face in this field and examine possible energy improvements.

This research employs a combination of interviews, simulations, and a case study. An existing Victorian building in the UK is evaluated in its current condition. The evaluation of comfort, energy consumption, CO₂ production, and daylighting analysis according to BREEAM is conducted using the DB software for existing design. Conducting interviews as a methodology technique, the authors seek to gain a deeper understanding of the challenges and difficulties associated with retrofitting a historic building. The forthcoming stage involves the examination of the existing design while interviews are conducted to ascertain any concerns and anticipations. The information gathered, along with the current planning policies and limitations, is utilised to formulate the proposed design. The outline of the research methodology is shown in Figure 1.

4. Case Study

The former Water Board Offices were built in 1865 by architects Shenton and Baker. They have been refurbished a few times and changed use through the years [53]. The building then changed use later to become a courtroom until 2018, when it became a bar. The bar closed in the pandemic, and the building has stayed vacant since then. Building information is shown in

Table 1. Building information.

Typology	Commercial Bar/Public house
Location	Leicester
Building Orientation	North-East
Density	Dense urban
Number of Floors	Two
Basement	It is used for technical equipment (50 m2)
Ground floor area	156 m2
Ground floor height	3.5 m
First floor area	156 m2
First floor height	4.5 m
HVAC	Gas boiler radiator heating with SCOP of 0.85
Heating controls	Time and Temperature Zone Control
Secondary Heating	N/A
Renewables	N/A
Heat Recovery	N/A
Ventilation	Natural ventilation with extraction fan in kitchen and restrooms
Hot Water	Stand-alone heater SCOP: 0.85
Lighting	Part L 2010 national policy lighting standards

N/A: Not applicable.

.

The ground floor has an entrance lobby, an open-plan entertainment area bar, a preparation area, and restrooms. The ground floor front and rear have four windows that show the Victorian era design. The back rear has a bay window, one window, and a fire exit door, as can be seen in Figure 2.

The first floor has similar plan features. The entertainment area is located in the front rear, which has three Gothic windows and a bay window. The staff room, office, and restrooms completed the plan. The fire escape door, which opens to a steel stair, is located in the back rear, as can be seen in Figure 3. The second floor does not exist anymore. It was used for storage when it was built.

The HVAC system of the building was identified as a radiator heating system and separates hot water with SCOP: 0.85. The bar was known as “Tiki” and had a beach concept, and was vacant for a while. Figure 4 shows the external and internal condition of the building. The lighting template is selected as Part L National, which gives a good response, and the schedule is adjusted to the pub light template, which means the building needs light between 3 p.m. and 3 a.m. Windows are wooden-frame single-glazing windows with a U-value of 5.7 W/m²K.

Figure 5a,b demonstrate the elevations of the building. Some of the building’s materials are not known. The author considered Qu et al.’s study [55], which is an evaluation of a Victorian house template for materials. There was no information about the ground floor. External wall thickness changes for every year. Therefore, thickness is assumed to be 35 cm for a solid brick wall. The existing building inner face is finished with plasterboard. The wood frame roof is covered with slate and roofing felt for the inner face. The ground floor is presumed to have a 40 cm cast concrete outer face, a 10 cm air gap, and finishes with wood floor finishing. Details of building structures are given in

Table 2. Details of building structures.

	Materials	Total Thickness	U-Value
External W	350 mm brick 13 mm gypsum board	463 mm	1.5 W/m2K
Roof	19 mm slate 38 mm wooden battons 100 mm air gap 13 mm plaster boards	160 mm	3.09 W/m2K
Ground Floor	50 mm flooring screed 100 mm air gap 100 mm brick slips 300 mm cast concrete	550 mm	2.0 W/m2K

.

5. Simulations

The DB software v7 is utilised to analyse existing designs by estimating energy consumption, assessing heating, cooling, ventilation, and building materials, and conducting simulations for daylight, sun paths, and shadows. A detailed building model is created based on location and dimensions, with U-values for components determined accordingly. The study evaluates refurbishment options to enhance energy efficiency and sustainability, proposing viable solutions that meet energy requirements. Results are analysed, contrasted, and discussed, with findings and gathered insights presented in the conclusions.

Activity templates are customised for each room according to particular requirements, with templates for the ground and first floors illustrated in Figure 6 and Figure 7, respectively. Heating and lighting schedules are established, and occupancy density, essential for internal gains, is computed utilising these templates. Each colour indicates the different areas and activities. Templates and schedules are copied and specified for each need.

The HVAC system, construction details, and other information are identified according to these requirements. All rooms’ thermal comfort demands are different. For example, the temperature of a preparation area where there is also kitchen equipment needs to be optimum at 16 °C. The model is created with the existing design and added the other buildings, which have an effect on heating and solar gains. Figure 8 shows the building elevations from DB software.

5.1. Monthly Temperature Analysis

Figure 9 illustrates the variations in perceived temperature indoors and outdoors. In July, despite the outside dry-bulb temperature being 16.51 °C, the indoor temperature feels warmer at 24.17 °C. The World Health Organisation recommends that the minimum ambient temperature for humans should be 18 °C [56]. However, for more susceptible populations such as the elderly, children, and individuals with chronic illnesses, a higher ambient temperature is considered even more ideal. Activity templates and schedules are adjusted according to the demands of the building and occupants. The bar is a crowded place, and occupancy density is high, which affects the heating load. The bar needs natural ventilation through the chimneys and openings, or a cooling system can also be considered. Preventing heat loss and increasing the U-value of the building components will support building comfort and reduce energy consumption. Insulating the roof, ground floor, and wall internally can be a strategy to improve human thermal comfort.

5.2. Internal Gain Analysis

The solar gain from the windows is measured at 117.28 MWh, while the occupancy is 3.43 MWh, and for computer and equipment usage, it is 4.40 MWh, as can be seen in Figure 10. The bar hosts many customers during the day. Considering the significance of occupancy, it is crucial to consider both heat gain and natural ventilation requirements.

The application of a sun-reflecting film on the windows will effectively decrease the amount of heat transferred from the outside. Occupancy can be limited to an average amount. Control panels can help to reduce energy consumption, for which equipment and computers are responsible.

5.3. Fabric and Ventilation Analysis

Unintentional air permeability through construction materials results in the loss of 29,478.16 kWh of heat. The structure lacks proper airtightness. The building’s information sections listed building elements with U values that exceed the recommendations set by the Part L standard [33]. Solid wall construction changed through the years. Chimneys, which are responsible for ventilation alongside heating, are not used and closed. This causes moisture problems for the building and has an effect on human health.

5.4. Energy Consumption Analysis

Within the room, the equipment utilises 4401.71 kWh, while the lighting accounts for 8010.46 kWh, and the DHW (Domestic Hot Water) consumes 83.21 kWh. Figure 11 shows the fuel breakdown analysis result. Notably, heating contributes the highest energy consumption, reaching 64,853.73 kWh. However, this falls short of meeting the minimum requirement of 130 kWh/m² set by the CIBSE TM46 guideline [57].

5.5. Daylighting Analysis

Daylighting analysis is carried out according to BREEAM standards. Two rears have windows. Therefore, the results are not efficient. Closed windows with opaque material, restrooms, and storerooms are not considered for calculation. Figure 12a,b show the ground-floor daylighting analysis and the first-floor daylighting analysis. The primary objective of simulation is to evaluate the necessity and impact of natural light in a building.

The assessment of the simulation is conducted based on the prescribed standards set by BREEAM. To meet the requirements for a successful evaluation, the building must achieve a pass under the perpetually clear sky conditions defined by the Commission International on Illumination (CIE). Additionally, a minimum of 80% of the occupied areas within the building’s net floor space should be sufficiently illuminated by daylight. The total area is 255.5 m², which needs daylighting. The result shows that the status is a failure, which can be seen in Figure 13.

5.6. Annual CO₂ Production

The carbon dioxide (CO₂) emissions of the building were estimated to be 20,493.51 kg/year, as can be seen in Figure 14. Reducing CO₂ production is the goal of every nation that signed the directive. In 2014, the European Council outlined that a minimum of 32% of the energy consumed should come from renewable sources. Furthermore, there was a target set for improving energy efficiency by at least 32.5% [58].

6. Interviews

As a research method, an interview will help to identify the challenges and current situation of the building. Occupants who live in a historic building and who want to live in it and architects participated in the research. The main goal was understanding the awareness of people and challenges they faced when they decided to improve the energy efficiency of the historic buildings. The goal was to interview twenty people. However, overall, ten people participated. Local authorities did not consent to participate but gave some information about policies.

The participants were given thorough information regarding the goals, procedures, and possible dangers of the study before the interviews started. The ethics procedure was explained. No personally identifying information was gathered, and data were safely kept using encryption to guard against unauthorised access in order to maintain confidentiality and anonymity. The research methodology was meticulously crafted to mitigate any possible harm to the subjects, steering clear of delicate and upsetting questions. The primary focus remained on utilising the research findings to benefit society while safeguarding the participants from any harm. Throughout the entire process, data processing and disposal were carried out diligently, upholding participant rights and privacy by adhering to these ethical standards during the interviews. The interviews were conducted online with all participants. Semi-structured interviews with ten participants from different backgrounds contributed to the study. The interviewees were categorised according to city, background, and occupant numbers.

Table 3. Interviewee details.

Interviewees	Building Location	Description
Interviewee 1	Nottingham	Victorian semi-detached house
Interviewee 2	Nottingham	Victorian semi-detached house
Interviewee 3	Nottingham	Built in 1890 with special windows
Interviewee 4	Nottingham	Built in 1880
Interviewee 5	Glasgow	Built in 1870
Interviewee 6	Inverness	Victorian house, built in 1860
Interviewee 7	Nottingham	Architect works for an architectural Office
Interviewee 8	Nottingham	Architect works in Nottingham
Interviewee 9	Leicester	They live in Leicester and want to move to a historic building
Interviewee 10	Leicester	They live in Loughborough and want to move to a historic building

shows the details of the participants.

6.1. Interview with Historic Building Occupants

Six people from different locations participated in answering the questions about the existing condition of their building and challenges they face during energy retrofits. The context and the questions are presented below with each interviewee’s answers.

• Understanding the Current State:

• Can you describe the existing condition of the historic building you are associated with in terms of energy efficiency and CO₂ emissions?

Interviewees were confused when they heard this first question and needed to think about it for a while. Interviewee 3 replied, “I’m sorry to say the building is big and rambling and is not at all energy efficient. We have a big fuel bill”, while interviewee 5 replied that they have double glazing and a biomass boiler. Interviewees 1, 6, and 2 described their houses as inefficient because the intervention cost is so high and is not affordable. Interviewee 4 resides in a ground-floor flat of a Victorian-era brick home that is part of a Grade II listed building. The property is insulated by flats above and below. It features double-glazed windows and a gas boiler heating system (retrofitted in the 1980s) with five radiators, excluding the kitchen. The occupants economise energy use by limiting showers, laundry, and central heating. They lack energy efficiency statistics but could obtain them. They are interested in exploring more efficient and sustainable heating systems, such as electric storage heaters, but solar panels are not feasible due to the building’s listed status.

2.

Challenges Faced:

• What challenges have you encountered or foresee when it comes to retrofitting the historic building to reduce CO₂ emissions?

Interviewees 1, 2, 3, and 6 stated that financial challenges and being able to source a reliable builder to retrofit their houses were issues. Interviewee 4 noted that their Grade II listed building requires permissions for external modifications, prohibiting wall insulation, and that retrofitting is costly without subsidies. Interviewee 5 highlighted that grants are not retroactive, citing the need to pay for a biomass boiler due to long application times, and emphasised the financial and bureaucratic challenges of sustainable practices.

3.

Policy Influence:

• How do existing policies and regulations influence the decisions made during the retrofitting process to improve energy efficiency and reduce CO₂ emissions?

Interviewee 5 stated that ‘retrospective applications are not allowed when the homeowner had to change the boiler’, as an example. They underlined that homeowners in the UK are not aware of the availability of grants and schemes. Conversely, interviewee 4 answered that they are not familiar with current policy and regulations, as their heating costs are relatively low, and they have not investigated a newer retrofitting. Interviewees 1, 2, and 3 did not make any interventions to improve energy efficiency, while interviewee 6 stated that they would follow any building regulations and legal requirements but would need to ask the builder for advice.

4.

Balancing Heritage and Efficiency:

• During the retrofitting process, how do you balance adopting energy-efficient technology with maintaining the building’s historical features?

Interviewee 4 said that using original reclaimed sash windows, applying a double-glazing treatment to them, or having new windows made in an authentic Victorian fashion would be a compromise solution to the problem of heat escaping through poor insulation. The other forms of heating are concealed (a boiler in a storage cupboard) or not too obtrusive (radiators throughout). Interviewee 5 and interviewee 6 preserve the heritage while increasing the energy efficiency using double glazing while keeping the original frames and features. Interviewee 1 honestly answered, ‘I don’t think we really consider the historical look, but we make the changes to our house that suit our taste.’ Interviewee 2 and interviewee 3 mentioned that they prioritise the historical aspects.

Residents who want to live in a historic building, interviewee 9 and interviewee 10, were not aware of current policies. Both were interested in the historical aesthetic of the building. They do not know of the challenges of living in a historic building. In addition, they supposed that they could implement every intervention in the historic building. They also mentioned that they faced a shortage of refurbishment skills for new buildings and have concerns about finding skilled builders and workers.

6.2. Interview with Architects

Two architects answered the questions about the challenges they face during energy retrofit projects.

Architectural Perspective on Broader Impact:

• As an architect, how do you perceive the overall impact of retrofitting historic buildings on environmental sustainability, considering challenges and successes?

Both believe that the impact is meaningful, stating the following: “Retrofitting is the first strategy that should be explored before considering new builds. There are challenges, such as being constrained with many elements of the building fabric, but there are also many opportunities. Retrofitting, in many cases, is cost-effective compared to the alternative and embodied energy savings. In an attempt to preserve the historic fabric, the regulations can be very constraining. In some instances, it is not allowed to change windows to make them more efficient and dryline the walls internally to improve their U-value”. Interviewee 8 added that client demands, factors such as cost-effectiveness, and the lack of clarity in existing regulations create challenges in the design process.

Views on Promising Materials and Technologies from an Architect’s Standpoint:

• Are there specific materials or technologies that architects find promising or particularly effective in achieving energy efficiency goals in retrofitted historic buildings?

Insulation is becoming more effective every year and therefore thinner. This helps preserve more space internally while retrofitting historic buildings. Interviewee 7 replied, “I am not particularly aware of any new materials or technologies aside from this”. Interviewee 8 mentioned ASHP and GSHP as new technologies to apply.

Approaches to Navigating Restrictions and Regulations in Architectural Design:

• When faced with heritage preservation restrictions and regulatory frameworks, what approaches or design methodologies do architects employ to ensure successful integration into retrofitting projects?

Interviewee 8 says that the dialogue early in the design stages with the conservation officer can be very useful. Interviewee 7 believes a collaborative approach right from the start facilitates the process.

Evaluation of Current Policies from an Architect’s View:

• How effective are current policies in facilitating the integration of energy-efficient technologies during the architectural design process for retrofitting historic structures?

Interviewee 7: “In my opinion, conservation officers are always aiming to preserve the historic integrity of the building first and then potentially make it more efficient next. The current policies don’t particularly facilitate the integration of energy-efficient strategies, although the common goal for everyone is to keep the building in use”. Interviewee 8 added that reaching local authorities is a challenging process. Obtaining information on a matter can prolong the process or lead to the rejection of the application.

Architectural Recommendations for Policymakers:

• What recommendations would architects offer to policymakers to enhance the effectiveness of policies related to architectural design for retrofitting historic buildings for CO₂ emission reduction?

Interviewee 7: “Better training in the subject would be beneficial, I believe. Retrofitting historic buildings is not necessarily learnt or taught in school. These should be mandatory CPD topics from the Architects Registration Board. Building Conservation and Heritage is a core RIBA CPD, but not all architects are chartered, and not all have to do this training”. Interviewee 8 added that workshops run by councils and collaboration between professionals would be beneficial.

6.3. Findings

A total of 10 interviews were conducted. The interviews encompassed six individuals residing in historic buildings, two individuals aspiring to reside in such structures, and two architects. While the sample size is relatively small and may not allow for broad generalisations, the findings contribute valuable insights into the impact of retrofitting in the UK as a strategy for improving energy efficiency and the challenges associated with its implementation. The limited number of participants was due to accessibility constraints as well as participant availability, yet the data collected provide meaningful perspectives on these critical issues. Findings are shown in

Table 4. Key findings from interviews.

Participants	Key Findings
	The participants exhibited a lack of awareness regarding existing policies and grants.
	The majority expressed a keen interest in architectural design and the various components involved.
Residents	Cost effectiveness emerged as the primary objective for the participants.
	The interviewees displayed a lack of knowledge regarding interventions aimed at reducing energy consumption.
	Difficulties were encountered in reaching out to professionals and obtaining guidance in this domain
	Concern about lack of understanding the current regulations.
Architects	Retrofitting skills shortages.
	Clients demands—Delayed response from the local authority.

.

7. Enhancing the Historic Building’s Energy Efficiency

The function of the building is presumed to be a community centre that brings communities together to raise awareness and be an example of a sustainable building with low energy consumption. Improving energy efficiency in historic buildings started with retrofitting the public buildings [27]. Therefore, a new function is proposed and examined in DB software. This section presents and evaluates several possible approaches. DB with databases will be used to assess each option to understand the consequences of lowering energy and CO₂ emissions.

7.1. Proposed Interventions

The proposed interventions are described in

Table 5. Proposed interventions to improve the energy efficiency of the building.

Intervention	Description
Insulations	Insulating roof, ground floor and external wall internally
Glazing	Slim double glazing for every window
Lighting	Upgrade to Led lighting and adjusting lighting schedule
HVAC	Ground-source heat pump
PV North	70 m2 PV
PV South	Restrictions about solar panels do not allow to apply; historic façade concerns

.

• Insulation

The first intervention is to insulate the external wall internally, between roof rafters and the ground floor.

Table 6. Intervention (insulation) details.

	Materials	Total Thickness	U-Value
External Wall (internally)	350 mm Brick 120 mm XPS 13 mm gypsum board	483 mm	0.236 W/m2K
Roof	19 mm slate 30 mm vapor-permeable felt 38 mm wooden battens 250 mm XPS 50 mm air gap 13 mm plaster boards	400 mm	0.9 W/m2K
Ground Floor	50 mm flooring screed 100 mm glass fibre 100 mm brick slips 300 mm cast concrete	550 mm	0.125 W/m2K

demonstrates the insulation details for each element. It is impossible to add layers externally due to restrictions that apply according to current policies. The building façade has an architectural value that makes it unique and limits the interventions. The existing design has plasterboard layers internally, which gives the opportunity to add insulation as a solution. XPS extruded polystyrene is applied with a thickness of 120 mm and 13 mm gypsum plasterboard added internally. The addition of external walls internally, the roof between rafters, and the ground floor between wood structures under wood flooring will be insulated. Cross sections are shown in Figure 15. The existing design has an air gap to provide enough space for underfloor heating pipes and insulation.

After improvements, the U-value of the external wall decreased from 1.5 W/m²K to 0.236 W/m²K, while the ground floor U-value reduced to 0.9 W/m²K from 2.0 W/m²K. The main impact on reducing U-value belonged to the roof with 0.125 W/m²K, which was 3.09 W/m²K. Roof loft gives the opportunity to apply insulation. All parameters depend on the existing conditions of the building. Therefore, it can be changed for every building. However, this building retrofit process and proposal will help to create a guideline for the same kind of building for identifying retrofit strategies.

• Glazing

Putting in slim-profile double glazing in place of single glass is the best solution for historic buildings where replacing the windows is not an option. Slim-profile double glazing typically exhibits a lower thermal performance compared to traditional double glazing, yet it demonstrates considerably superior thermal performance when compared to single glazing [59].

• Lighting

Existing design lighting is used for the bar concept, which consumes a large amount of electricity. The restrooms, preparing area, staff room, and offices have LED bulbs that are suitable according to the Part L 2010 edition. Upgrading to LED lighting and designing a suitable schedule and control panel will help to reduce energy consumption, which is what lighting is responsible for.

• HVAC

The utilisation of a ground-source heat pump proves to be a highly effective approach, provided that the building environment is suitable and local authorities grant their approval for this intervention. By employing the same system as the HVAC for hot water, the consumption of electricity can be significantly reduced. The existing building has a basement, which provides enough space for mechanical devices and equipment such as a boiler tank. Implementation of the system will not affect the façade, and the system will work through existing openings that already work for the heating system.

• PV

Adding PV is not a common strategy for a historic building’s energy retrofit. Interventions made to the roof and façade are not allowed. However, if panels do not seem to be from the street view and local authorities agree with that option, it can be applied to the building roof with a suitable orientation [20]. Existing building roof systems give the opportunity to place PVs. Nevertheless, PVs will face towards the north, which is not as efficient as the south. On the roof, 70 m² of photovoltaics was installed. The improvement description is given in

Table 7. Description of improvements and existing design.

Improvements	Description	Existing Design
Insulation	External wall inner face Roof (between rafters) Ground floor slab	No insulation
HVAC system	Ground-source heat pump	Boiler/radiator
Windows	‘Slim’ double glazing	Single glazing
Lighting	LED lighting control	Led-2010 National
PV	Northeast (30 solar panels)	No solar panels

.

Findings from the literature review and interviews showed that people’s awareness is very important for energy retrofits. People should be influenced and learn from the community, especially about the policies and rights they have. Therefore, an existing building that has been used as a bar for years and nowadays is vacant can be a focal point for the community. Based on the findings from interviews and existing design simulations, the building is presumed to serve as a community centre, aiming to bring communities together, raise awareness, and serve as an exemplar of a sustainable building with low energy consumption.

7.2. Impact of the Retrofit Strategies

The building’s total electricity consumption is 6516.60 kWh for a year, while total gas consumption is 7635.41 kWh after retrofitting strategies are applied to the building. The power consumption is 2382.60 kWh, as can be seen in Figure 16. Adjusting the appropriate schedule for equipment and reducing the unnecessary devices that have been used for the bar concept and its change for the proposed design reduced the energy consumption for room electricity by 6% to 4134 kWh from 4401.71 kWh.

Interventions that are applied to the building as energy retrofit strategies have a great impact on reducing CO₂ emissions. Insulating the ground floor, roof, and external wall internally while considering restrictions; changing window glazing from single to slim double glazing; improving lighting to LED; considering GSHP instead of a traditional boiler; and adding PVs can decrease the building’s CO₂ production.

After these interventions, CO₂ production is reduced to 1274.76 kg/year, which is shown in Figure 17.

8. Discussion

The specific historical structure examined in this study showcased the remarkable potential of this building type for conserving energy and reducing greenhouse gas emissions. This was made possible through the implementation of improvements to the building envelope. The implementation of wall enhancements, HVAC system optimisation, and the utilisation of minimal appearance photovoltaics played a significant role in achieving substantial savings of 100% and 88.2% for electricity and natural gas consumption, respectively, as can be seen in

Table 8. Comparison table for energy consumption of existing and improved designs.

Parameter	Existing Design	Improved Design	Absolute Reduction	Percentage Reduction
Lighting (kWh/year)	8010.46	2382.60	5627.86	70.3%
Room Electricity Consumption (kWh/year)	4401.71	4134.00	267.71	6.1%
Heating Gas (kWh/year)	64,853.73	7614.92	57,238.81	88.2%
DHW Gas (Electricity) (kWh/year)	83.21	20.49	62.72	75.4%
Total Electricity (kWh/year)	12,495.38	0	12,495.38	100%
Total Gas (kWh/year)	64,853.73	7635.41	57,218.32	88.2%
CO₂ Emissions (kg/year)	20,493.51	1274.76	19,218.75	93.8%

. It is shown that the energy efficiency measures enable reductions of 88.2% and 100%, respectively, in the thermal and power usage. In total, 7238.16 kWh is produced by solar panels, which are located to the north, and the nearby library will receive the leftover energy. The power consumption can be decreased from 8010.46 kWh to 2382.60 kWh by using LED lamps in place of the current bulbs and turning on the lighting control. This equates to 70.2% energy savings.

9. Conclusions

In the United Kingdom, a significant proportion of homes were built at different periods in history. Specifically, 20% of the total number of homes were constructed before the year 1919, while 24% were built after the year 1980. This means that many historic buildings, which are defined as built before 1919, exist.

Improving the energy efficiency of current buildings is crucial for mitigating the consequences of climate change and addressing the problem. Structures that are historically and culturally significant must be given consideration within this category. In addition, energy retrofits can reduce building energy use and carbon emissions, but they are challenging to implement in historically significant and conventionally built structures. Furthermore, even when these buildings achieve their energy-saving targets, there are frequently insufficient laws regarding interventions. Planning is crucial for the preservation and repair of these buildings, and increasing their energy efficiency frequently presents significant challenges.

Firstly, assessing the actual energy usage of historical structures in the UK is crucial. There has not been much thorough research on energy-saving strategies for historical structures. Therefore, the goal of this study was to contribute to the data of knowledge by figuring out what causes historical buildings to consume a lot of energy and then creating workable solutions that preserve the buildings’ architectural value while still complying with modern regulations.

According to this information from literature reviews, interviews, and case studies, interventions were applied, and the results are shown using DB software for each one. The impacts of the interventions and restrictions that should be considered led to the study. A comprehensive retrofit strategy was applied to the existing building. A couple of comparable tables that showed the differences between the U-value, energy consumption, CO₂ emission, electricity, and gas consumption were introduced. The research results indicate that historical buildings, where energy-efficient technologies are often overlooked due to architectural limitations within the building or the surrounding area, can still experience a significant decrease in energy usage and greenhouse gas emissions.

Despite a lack of understanding of regulations, existing guides provided by the IHC, Historic England HiberAtlas [60] tool, and STBA were helpful in proposing the best strategies that can be applied. The building is in a conservative area in Leicester. Therefore, external insulation cannot be considered an improvement. Internally, insulation can be applied due to the existing solid wall already covered by plasterboards, and the room area offers this opportunity. Existing floors have a 100 mm air gap under the flooring, indicating a possibility for insulation. Similarly, the roof has a loft that is not occupied, making it implementable between rafters.

Adding PV was the most important intervention, which has restrictions about its implementation. However, local authorities should analyse the application and decide if it is acceptable. The angle of the PVs and the appearance from the street were the keys for proposing solar panels. Although the front rear is the most effective, PV is considered and calculated according to the back rear. Changing windows is another problem to be solved. If windows have architectural and historic significance, changing them cannot be considered. However, adding second glazing or changing single glazing to slim double glazing is a good intervention regarding the impact on the building. Despite the size of the frame thickness, changing glazing has a great impact on energy consumption. Figure 18 shows the guide for implementations.

10. Recommendations

It is paramount to engage highly qualified professionals and perform a thorough early-stage risk assessment of the building to identify potential challenges and mitigate risks in the retrofit process. This proactive approach enables effective management of the project, reducing the likelihood of delays and unanticipated costs. Early risk identification facilitates the creation of a realistic timeline and financial plan, allowing for smoother implementation and adherence to project objectives. Moreover, conducting a detailed cost analysis is crucial for assessing the financial viability of the retrofit project. This evaluation aids in accurate budgeting and resource allocation, ensuring the retrofit is completed within the available financial framework. Additionally, addressing any deviations from established technical specifications in a timely manner is vital. Swift intervention helps maintain the integrity of the retrofit, ensuring that the project conforms to the required technical standards and avoiding unnecessary expenditures due to rework or scope changes.

Incorporating heritage authorities into every phase of the project is also essential to ensure compliance with heritage protection regulations while preserving the historical significance of the building. Heritage conservation presents unique challenges in retrofit projects, where the need to integrate modern energy efficiency standards with historical preservation often requires expert guidance. Involving heritage authorities throughout the retrofit process ensures that the building’s cultural and architectural values are preserved without compromising on the efficiency and sustainability of the interventions. The implementation of these strategies is critical for preventing excessive costs, avoiding project delays, and minimising disputes between stakeholders. Furthermore, a common challenge in the context of retrofitting historic buildings is the lack of understanding and clarity among homeowners. Without clear guidelines, homeowners may hesitate to pursue energy efficiency upgrades, opting instead to rely on exemptions provided by building regulations for restoration efforts. This issue, acknowledged by the UK government in a publication from January 2024, highlights the need for improved communication and clearer regulatory frameworks. To mitigate this, policymakers should focus on revising current regulations to enhance clarity and prevent confusion. Moreover, introducing certification programmes that develop specialised skills among professionals working on historic building retrofits would be beneficial. These programmes can bridge the knowledge gap and improve the overall quality of retrofit projects. Local authorities can also play a significant role in raising awareness by organising workshops and providing resources to help homeowners and contractors understand energy efficiency measures and their regulatory requirements. These actions will contribute to the promotion of sustainable and well-informed retrofit practices.

While preserving heritage is crucial, addressing climate change is equally important. The threat of global warming demands urgent action to reduce CO₂ emissions, which necessitates sustainable building practices that reconcile heritage conservation with modern environmental standards. Just as the introduction of electricity and fire safety regulations once reshaped buildings, today’s retrofit initiatives must balance historical preservation with the adoption of environmentally responsible practices. The case study analysed in this paper illustrates a fire exit stair located at the rear of the building, which affects the architectural aesthetics. This underscores the need for policies that strike a balance between maintaining architectural significance and ensuring the safety and sustainability of historic structures. Policymakers must evolve these frameworks to incorporate professional expertise, ensuring that both heritage preservation and environmental sustainability are achieved.

This study delves into understanding the impact of retrofitting in historic buildings in terms of energy efficiency. However, future research should focus on a comparative evaluation of the effectiveness and longevity of various insulation materials used in retrofitting, providing a more comprehensive understanding of their long-term performance and sustainability. Additionally, a detailed investigation into the cost-effectiveness of different retrofitting methodologies could offer valuable insights for optimising investments in energy efficiency improvements. Further exploration of these aspects would support evidence-based decision-making in retrofit strategies and contribute to the development of more effective policies for sustainable building practices.