Preserving the historical value and thermal properties of renovated buildings: The case of reconstructed town houses in Kosice, Slovakia

Abstract

The restoration of monuments is of great interest, leading to more architecturally significant designs. Many promising approaches to building design foster a symbiosis of the old and the new. The paper examines the compromises between the structural and physical properties of a historic building intended for renovation, which has already undergone several renovations. Due to the limited optimization possibilities at specific levels of the renovation project, diagnostics were used during the examination of proposals. Part of the diagnostics involves measuring thermal conditions, as well as temperatures on the internal and external surfaces of the building envelopes. The study demonstrates how the properties of the outer shell affect thermal insulation and suggests methods for architects, planners and preservationists to preserve the structural forms of the facade. The goal was to show that, despite the absence of a new thermal insulation layer on the outside of the building, the standard requirements are not violated. On the inner surface of the envelope walls, the temperature does not drop below the critical value for mould growth. Additionally, there are examples of modifications to the original details and their shape after the restoration of this building.

Headnote

Abstract The restoration of monuments is of great interest, leading to more architecturally significant designs. Many promising approaches to building design foster a symbiosis of the old and the new. The paper examines the compromises between the structural and physical properties of a historic building intended for renovation, which has already undergone several renovations. Due to the limited optimization possibilities at specific levels of the renovation project, diagnostics were used during the examination of proposals. Part of the diagnostics involves measuring thermal conditions, as well as temperatures on the internal and external surfaces of the building envelopes. The study demonstrates how the properties of the outer shell affect thermal insulation and suggests methods for architects, planners and preservationists to preserve the structural forms of the facade. The goal was to show that, despite the absence of a new thermal insulation layer on the outside of the building, the standard requirements are not violated. On the inner surface of the envelope walls, the temperature does not drop below the critical value for mould growth. Additionally, there are examples of modifications to the original details and their shape after the restoration of this building.

KEYWORDS Historic building; Reconstruction; Building restoration; Historical monument; Historical survey

1. Introduction

Historical centers in many Central European countries comprised of historic buildings that are several hundred years old and often built of stone or from traditional masonry elements, such as stone blocks, bricks block, and other piece masonry materials. The wall thickness of historic buildings is significant providing sufficient protection from high temperatures in summer, but usually do not meet the strict criteria for thermal protection during winter. The thickness of the walls and the material used depend on when the building was built. Such buildings have sometimes been rebuilt, renewed, adapted several times. Before renovation, each building must undergo inspection to diagnose all structures, their defects and faults. If the renovation or refurbishment of an old building is planned, specific interventions must be considered. A new building is treated differently from a historic building according to valid standards. The specifics are especially important for buildings that have historical value and are a part of the cultural heritage. The protection of monuments is one of the responsibilities of society, and society must devote itself to the protection of its cultural heritage (Kiinzel, 2009; Mine, 2013).

1.1. Review of literary sources

If we consider the revitalization of historical buildings from the perspective of protecting cultural and historical heritage, it involves not only an intervention in the layout and typology of the building, but also in its structural elements. In the literature, various approaches to reconstructions of individual structures can be found (Carbonara, 2012; Cárdenes et al., 2014; Murgul, 2014; Sahmenko, 2015; Valluzzi, 2014). The approach to the problem depending on whether the buildings are made of bricks and stone (Kalousek and Mohelnikova, 2014; Ucer et al., 2018) or of brickwork and wooden supporting elements (Akcay, 2022). Naturally, repairing and renovating different buildings require different technological approaches. The approach varies when dealing with civil buildings (Lee, 2019; Morrish and Laefer, 2010; Omishore et al., 2019; Yazgan and Unay, 2020), church buildings (Penica, 2015), or possibly industrial construction and industrial architecture (lvashko, 2019). In Central Europe, the historical parts of city centers, including churches, are mostly made of stone (Ribera, 2020). In the northern and northwestern parts of Europe, residential buildings as well as church buildings in cities are often built of wood (Mosoarca and Gioncu, 2013). Approaches to cultural heritage protection differ in Asia (Milosz, 2020; Taylor, 2004), Eurasia (Weiler and Gutschow, 2017), and other parts of the world. Research on the protection of cultural heritage can be found in the works (Curovié et al., 2019; Latham, 2016).

The common topics of works focused on historical objects are significant restoration, revitalization, and preservation of monuments (Fais et al., 2018). However, trends are divided not only into research on cultural heritage but also into research on structures and materials (Ferretti, 2014). These materials are commonly available and used for renovation, or they are new materials. Common calculation methods or simulation methods are used for construction calculations (Katunska, 2019; Saba, 2018). The combination of computational simulation methods and insitu measurements is a basic tool for investigating the structural elements of historical buildings (Labovska, 2016). Some significantly renovated historic buildings must also show an improvement in the thermal insulation properties of the perimeter constructions (Milone et al., 2015; Pisello, 2014). Attention must also be paid to critical details that show large heat leaks. To achieve satisfactory values, it is sometimes necessary to perform measurements directly insitu or experimental measurements in the laboratory (Webb, 2017). The evaluation of the energy demand of historical buildings can be found in the following research, Pracchi (2014), Mazzarella (2015), or also Ciulla (2016), Galatioto et al. (2019). Related issues concerning airtightness is presented in the source (Katunsky, 2013). The design, planning and modeling of the reconstruction and restoration of historical buildings also includes many new methods (Mehdinezhad et al., 2021; Radziszewska-Zielina, 2017).

1.2. Requirements for restoration of historic buildings

In the case of building modifications such as renovation, it is necessary to observe the basic rules that apply to the monumental, historical value of the building. Attention must be paid to the basic requirements of a major renovation and to the best methods and procedures of construction research, as published by Nemec et al. (1994). In addition to the properties of the structures, the research of the conditions of the internal environment in historical buildings is crucial as well. Moreover, it is necessary to check the properties of the materials used and at the same time the extent of damage to the structures from which the building is built. If the building is on the list of cultural monuments, it is necessary to approach the restoration with a particularly sensitivity and preserve the monumental value of the building. If there are architectural elements on the facade that do not allow interference with the external appearance, it is possible to insulate the building from the inside. To diagnose the thermal-technical properties of the envelope of a building, it is necessary to perform in-situ test measurements.

Requirements for the reconstruction and restoration historic buildings can be seen in Fig. 1.

Restoration of historical buildings is a highly complex process that involves the application of only known building materials, and it is necessary to know their effect on the specific type of originally used historical material. The current challenge for procedures in the field of protecting historical heritage is the application of hidden methods of insulation, which preserve the authenticity of a property and other cultural monuments in areas of cultural heritage. Adequate use of the monument fund ultimately means maintaining the sustainability of the operation of historic buildings.

With the influence of the development of new materials and new construction processes, the possibility of interventions in historic structures that do not endanger the monumental values or use of the historic building is gradually expanding. As mentioned earlier, this is mainly due to the use of modern, progressively sophisticated materials, as well as new construction technologies that are being implemented. The monitoring of materials is intended not only to affect the structure of the building, but also to improve its structural and physical properties as well as enhance the internal environment.

2. Materials and methods

The subject of the research is a selected historic building in the centre of Kosice, Slovakia, in Central Europe. Not all historic buildings are on the list of cultural monuments. The building that is the subject of this case study is a monument; therefore, it had to be restored very sensitively. Dating back to the end of the 13th and the beginning of the 14th century, the building's historical significance dictates careful restoration practices. As a result of its status as a monument, strict adherence to all prescribed thermal insulation properties of the building envelope (walls, roofs, windows), as mandated by the Act on Energy Efficiency of Buildings for new constructions, was not required. If meeting the prescribed standards for the monument is not required, it is necessary to consider conditions for restoration design in order to ensure the sufficient thermal protection of the building. During the design phase, it is essential to identify the physical properties of the authentic structures in real conditions. However, this task is not always straightforward. This paper deals with a case where the improvement of thermal protection is expected, but due to the fragmentation of the facade it is not possible from outside. The result is the determined temperatures and insulation properties of original perimeter walls obtained directly in-situ. Furthermore, the article presents historical research and provides a picture of the building before and after the restoration.

The objective of this research was to outline the preparation process for the renovation and restoration of an old building situated in the historic centre of Kosice, Slovakia, in Central Europe. The building, constructed long ago, serves commercial purposes and has undergone multiple renovations. However, its original construction did not meet the standards required for its intended use. Consequently, an inspection was necessary before commencing the restoration project.

The aim of the contribution is to demonstrate, through calculation and experimental measurements directly (insitu), that under extreme conditions (low outdoor air temperatures in winter) the critical temperature for mould growth does not occur on the inner surface of the envelope walls (two facades). Flowchart of the study can be seen in Fig. 2.

2.1. Case study

The selected building is situated on the main street in Kosice's historical centre, close to the Gothic Cathedral of St. Elisabeth. It is part of complex "6", located at the intersection of "Alzbetina" and "Hlavná" streets (see Fig. 3). The construction period of the building dates back to the 13th century and 14th century, with a Baroque reconstruction completed in the 18th century (Kolcun et al., 2018).

Details related to the historical survey are shown in Fig. 4, where a) profiled stone in the lower layers of parapet cornices, indicates settlement dating back to the Renaissance period, and b) stone plinth around the perimeter of the building was constructed according to the original architectural design element. The location of the stone window sill ledges was confirmed through sounding on the 2nd and 3rd floors, suggesting probable settlement dating back to the Renaissance.

The building is constructed based on Gothic plans, and throughout its various developmental stages, it was formed according to the stylistic requirements of different periods. The morphology of the building has been preserved with distinct stylistic elements, among which the most significant for the subject of this study are the Gothic stone parapet cornices, stone parts of the windows, the "shambranos", the stone corner reinforcement and rich stucco decoration in the place of the avant-corps. The term avant-corps (in Italian risalto-protrusion) refers to the central or lateral part of a building protruding along the entire height from the face of the facade up to the depth of one window axis. In this case, it is the central protruding part of the building, which is intricately divided and decorated (see Fig. 5).

The primary building material is quarry stone mixed with fully fired brick. The initial layer of plaster is associated with the Baroque-Classicist morphology. It consists of a

mixture of river sand of a coarser fraction and lime. The plastic stucco decoration of the facade is related to the unpreserved elements of the Rococo facade, albeit some of them are not preserved, having been partially overlaid. The ornaments above the windows in the avant-corps are based on the original Rococo decoration, and similarly, the plastic stucco decoration of the windows has been preserved.

Restoration of the facade of this cultural monument-originally the Jesuit University of "Beñadik Kisdy" (the so-called Kisdyanum), situated opposite the western facade of the Cathedral of St. Elisabeth, was carried out under the methodological auspices of the Regional Monuments Office, responsible for monument restoration.

The final stage of the restoration project involved the refurbishment of the eastern part of the facade facing streets "Hlavná ulica" and the northern facade facing "Alzbetina ulica". It is located up to the already restored middle avant-corps. While cleaning of the facade, the stone linings of the window openings dating back to the last quarter of the 15th century were discovered under the damaged plaster and had to be preserved.

2.2. Calculation of thermal protection

The monitoring and survey of the historic facade of the building in the historic city center were conducted in winter. Surface temperatures were recorded indoors, outdoors and on the building envelope (one-dimensional heat dissipation). The facade of the outer wall features significant architectural elements made from various building materials. Under unfavourable conditions, i.e., in terms of temperature differences and other atmospheric influences, these architectural elements may experience disturbances.

The aim of inspection was to determine the thermaltechnical properties of the building structures and details before the restoration. The thermal properties are expressed by the thermal resistance R and the heat transfer coefficient U. In a historic building, these properties can be determined by measuring the heat flux density д (W/m?) in the winter period. The heat flux density transfer can be calculated from the measured temperatures of the inner surface of the envelope wall 95; and the outer surface of the envelope wall (facade) 6:

... (1)

Heat flux density on the inside of the building (convection):

... (2)

Heat flux density on the outside of the building (convection):

... (3)

If the measured values of surface temperatures, as well as indoor and outdoor air temperatures, are known, we can calculate the heat convection coefficients hi and he, thus:

... (4)

... (5)

It does not matter whether we measure the heat flow density during conduction, transition or transfer, it is always the same value q (W/m?) (Energy Conservation Act). When the equations have q on the left side, we can also put the right sides into equality. Thus, we can determine by measuring the heat transfer coefficient U (W/m?K):

... (6)

... (7)

The reconstruction of a historic structure, especially the facade of a building is a complex process. The objective is to minimize the impact on the building envelope in order to maximize the impact of the recovery. However, this is often challenging, due to a lack of knowledge regarding the building's structures and its envelope. In particular, designer often lacks essential information that needs to be quickly and non-destructively examined within the building in structures, including materials, structural geometry, perimeter wall materials, thermal-physical properties. Merely inspecting the building is insufficient; genuine experimental measurements are necessary. These measurements enable a more accurate and effective design of measures aimed at improving hygro-thermal behavior. Above all, it allows the historical value of the century-old facade of the object to be preserved.

3. Experimental measurements in-situ

For the purpose of in-situ test measurements, a room with windows facing north and east was made available on the 2nd floor. Monitoring the surface temperature under real conditions provides insights into the current state of the envelope structures of the building. The collected data can be applied to create a numerical simulation model. Measurements were performed on the external perimeter walls of the selected building. A similar measurement was previously carried out by the authors (Katunska et al., 2019; Katunsky, D. and Katunska, J., 2020). Thermal bridges play an important role in historic buildings, the diagnosis of which requires, in addition to measurement, evaluation based on integral calculation methods (Alkadri, 2024).

A view of the measuring apparatus and the sensors that record the temperatures and heat flows can be seen in Fig. 6.

Data loggers were used to collect the measured data, which was recorded in an hourly step. PT, Ntc, and NiCr resistance temperature sensors with a measuring range of -50 °C to +125 °С (-58 °F-257 °F) and a hundredth resolution with an accuracy of +£0.05 К were used to measure the temperature. Density of the heat flows is measured in the scope of -260 to +260 W/m? with a resolution of hundredths.

The historic building envelope has a significant heat accumulation primarily evidenced is mainly by minimal fluctuation in the interior surface temperature over time. Standard requirements determine the minimum temperature threshold for the internal surface, prompting the recommendation for continuous heating. When evaluating the thermo-technical properties of a building envelope, consideration is given to the steady-state temperature-assuming constant outdoor and indoor temperatures-although this partially disregards the envelope's heat storage capability. A fundamental criterion for assessing the envelope building structures from the thermotechnical point of view is the hygienic criterion, represented by value of the internal surface temperature. The decrease in internal surface temperature of the building envelope may lead to the condensation of water vapour and the subsequent mould formation.

3.1. Boundary conditions for the assessment

The aim of the test measurement in real conditions was to capture variations in the surface temperature of the envelope resulting from dynamic fluctuations in outdoor air temperatures in-situ. The measurement is affected by constantly changing internal and external environmental conditions. According to the standard, all surface temperatures of the surrounding structures in rooms with a relative humidity o; < 80% must be expressed as a value of 6, which must be above the dew point temperature, thus eliminating the risk of mould growth. For indoor air conditions in Slovakia, this is the value of "critical temperature for mould growth", sigo = 12.6 °C (54.7 °F). It is as if the dew point on the surface were equal to the temperature at a relative humidity of not 100, but 80%. There is a 20% reserve for the safe use of the space.

Thus, when we talk about a temperature of 20 °C in the interior of the building, we mean 68 °F. The results of the experimental measurements in the tables are given in degrees Celsius and for reference, also in degrees Fahrenheit.

Selected monitoring points were distributed in order to take the assumed critical points of the building structure into account. This was necessary because the number of days when the average daily temperatures fell below zero during the year was limited. Therefore, the measurement in the building was short-term (7 days) performed at the end of January and the beginning of February (STN 730450, 2019).

3.2. Measuring points for q and temperatures

During the construction of the perimeter wall, the dimensions of the stone parapet slabs and the material from which the slabs were made were determined after consultation with the restorer. The placement depth is equal to the width of the board; this is about 250 mm, and the height of the board is about 150-200 mm. The exterior stone ledge is made of andesite tuff covered with stucco decoration. Window constructions are mounted on receding window sills. The sensors were mirror-mounted on the northern and eastern perimeter exterior walls of the building at the same points. Although the radiators are located under the windows, they have been switched off. During the measurement, the room was heated by only one radiator, which was not located under the window, but in another part of the monitored room.

Due to the small number of monitored points, a network of horizontal and vertical axes was used to mark them easily. The measurements did not include an evaluation of the moisture state of the building materials, as sampling and their subsequent evaluation were not possible. The effect of moisture on the thermal properties of building materials in historic buildings can be taken into account by estimating a higher value for the thermal conductivity coefficient in numerical calculations (Künzel, 2002). The measurement itself consists of recording the internal surface temperatures using sensors 0,; temperatures and plates for measuring density the heat flows q. The COMET sensor (0ai, pi) was used to record the indoor environmental conditions.

Thermal engineering measurements were performed at the points highlighted in Fig. 7, i.e., at the points on the north and east perimeter walls. The measuring points located on the north-facing wall are marked as A5, B8, and B9, and on the east-facing wall they are points A14, B11, and B10. The marking numbers depend on the location of these points these points. Experimental measurements captured both heat fluxes and temperatures at several points. Only the points marked with these labels were selected for this case study.

The points with increased heat flux q (W/m?) are characterized by a decrease in the temperature of the inner surface of the building envelope (points C7 and C12). As the surface temperature of the building envelope decreases, water vapour condenses and moistens the surface, creating the conditions for the growth of microorganisms. Restoration of a historic building is a complex process, as has already been mentioned. This process is accompanied by a lack of knowledge about the building envelope in several cases. Above all, information needs to be obtained quickly and in a non-destructive way. It is necessary to examine the perimeter wall of the building, especially its composition, thermo-physical properties of individual building materials. These can only be determined through measurement.

4. Results and discussion

4.1. Results of thermal and technical measurement

The measured heat flow density q through the perimeter wall of the building, in the north orientation, is higher due to greater heat loss. This is because the thermal resistance R is lower due to the stone sill, which has a much higher coefficient of thermal conductivity à.

... (8)

This is also due to a lack of sunlight. As a result of sunlight exposure on the east-facing facade, the temperature gradients in the wall are reduced, and at the same time, the value of the heat flow density is lower. A comparison of measured temperatures at selected points on the east and north facade can be seen in Table 1.

The thermal convection resistance of the inner surface of the perimeter wall (К) is expressed by means of the average values of the heat convection coefficient hi. Likewise, Rse is calculated according to the heat convection coefficient at the outdoor surface he.

... (9)

... (10)

Since it is necessary to determine the temperature on the inner surface, only the coefficient h; was calculated. For the monitored period, the average value of the heat convection coefficient h; is 0.14 m?K/W (B8, C7) for the sensor located on the perimeter wall of the building with the north facade. The average value of the heat convection coefficient h; is 0.16 m·K/W (B11, C12) for the sensor located on the east facade. The sensors recording the measured data were placed on the surface of the receding parapet masonry and also above the window ledge. The corner of the building is situated at the intersection of on the north and east sides. The adjacent room housed the original gas hot water heating system, which had an outlet and air intake through the ventilation grille. This fact, along with the receding parapet masonry, leads to a distortion of the measurement results. The lowest required surface temperature prescribed by the standard, 12.62 °C (54.72 °F) (the "hygienic criterion" requirement), is thus met. The measured average values of internal surface temperatures are higher than the "hygienic criterion". Only the value at point A5 was reduced to the limit of the "hygienic criterion", and only for a very short time, which is not dangerous. Due to the sorption surface, any moisture is absorbed into the plaster and evaporates in a short time.

The different orientation of the facades to the cardinal points shows the different surface temperatures detected by the sensors. For instance, the sensors placed at the site of a stone parapet ledge show that the surface temperature at point A5 (north side) is higher than A14 (east side) within 4 days. The difference in surface temperatures between the northern and eastern surfaces is not significant, only 0.20 K. If the surface temperatures at the location of the receding parapet masonry at points B8 and B11 are compared, it can be stated that the value of temperatures on the north wall is about 0.5 K lower than on the eastern wall. Sensors B9 and B10 (east) are located on a wall that is slightly thicker than the north wall, moreover, they are situated in the corner of the building (higher indoor heated area), and therefore, the highest surface temperatures are recorded. The outdoor and indoor conditions expressed by indoor and outdoor air temperature are shown in Fig. 8.

Graph of the indoor surface temperatures in the observed sensors-points B8, B9, and A5 can be seen in Fig. 9.

Graphical dependence and a comparison of the measured temperatures in the selected points B10, B11 and A14 are shown in Fig. 10.

A comparison of the measured temperatures (average, min., max.) in the interior, exterior air and in the selected points can be seen in Fig. 11. From the above, it can be observed that both the minimum and average outdoor air temperature fell below zero (was minus), i.e., the conditions for measurement were met. It can also be seen that the temperature on the inner surfaces did not fall below the required values due to good heat accumulation.

Temperatures on the surface of the window sill masonry during the whole measurement are at the limit of the "hygienic criterion". Temperature gradients affect not only the density of heat flow through the perimeter wall of the building and through the masonry sill, but also the thermal resistance of individual parts of the building envelope. The average measured values of the temperatures on the inner surfaces are higher than the lowest required surface temperature prescribed by the standard. This is good from the perspective of meeting the requirement of the "hygienic criterion" but also due to the good heat accumulation point of view. Based on the above, it was not necessary to insulate the building from the inside. From an architectural and monumental point of view, insulating from the outer surface is out of the question.

The values of heat resistance at convection on the inner surface (Rs) are expressed on the basis of average values calculated from the heat convection coefficients (h;) for the observed period (see Table 2).

Due to the dynamic changes in outdoor temperature over time, the aim of the experimental measurements in the selected historical object was to capture the fluctuations in internal surface temperature on the perimeter walls. The in-situ test measurement was influenced by several changing factors in both the outdoor and indoor environment. It can be stated that the changes in the internal surface temperatures of the perimeter walls under non-stationary conditions were recorded in this manner.

4.2. Results in terms of construction, indoor comfort, and architecture

The mentioned study revealed the requirements for the restoration of the monument, which can be listed as follows:

e It was necessary to preserve the original (historical) mass of the objects, including the surface treatment, original (historical) expression, material and spatial composition, and historical details.

e İt was crucial to respect the supporting system; the same or related technologies were applied during the rehabilitation.

e Due to the changes in the object's use after the adaptation, some constructions made of new materials were adapted to the new character mode of the object.

e Without a detailed focus and research of the monument, it would not be possible to carry out a high-quality restoration. To ensure sufficient thermal insulation quality of the building, it was necessary:

e Preserve the appearance of the facades of the historic building; in justified cases, it was possible to insulate the gable masonry with heat-insulating plaster.

e Use hidden forms of thermal insulation, if possible.

e Insulate the ceiling above the last floor, in the attic. It was necessary to preserve all the historical architectural elements of the building by:

e preserving or regenerating the entire historical essence of the facade and parterre (both material and aesthetic);

e preserving and regenerating the original fillings during renovation and modification of building facades;

e supplementing the missing parts of the details with copies with an emphasis on preserving-regenerating the sharpness of the profiling;

е professionally repairing the damaged parts of the stone;

е determining the color of the facades through evaluation of the survey conducted by preservationists in cooperation with the architect.

The sustainability and life cycle of historical buildings are also important (Zhou, 2022). Economic factors play a crucial role in determining the value of historical town houses. Preserving their historical value requires significant investments in restoration, maintenance, and upkeep. Economic considerations involve costs associated with materials, labor, and compliance with preservation regulations. Environmental implications have a significant impact, including energy consumption, resource depletion, and waste generation. The choice of construction materials, energy-efficient technologies, and sustainable practices can minimize environmental impact. Environmental efforts are increasingly important in determining property value, as sustainable and eco-friendly buildings are often more desirable to buyers. Preserving historical townhouses can impact the health and well-being of occupants and surrounding communities. Renovation activities may entail exposure to hazardous materials such as lead-based paint or asbestos, posing health risks. Indoor air quality, ventilation, and access to fresh air also affect residents' health (Bullova et al., 2021). Considering the technical-economic impact on the environment and health in preserving the value of historical urban houses involves balancing economic viability with environmental sustainability and public health concerns. These aspects increase the value of historical properties by protecting their cultural heritage, minimizing environmental impact, and promoting residents' well-being.

In one of the phases of the construction development of the building, ventilation openings were created in the parapet masonry during the installation of gas heating. This fact, along with other construction effects associated with the modification of the building, caused the surface temperature to be lower in the given place than recorded by other sensors. The influence of the facade profiling on the thermal-technical properties of the perimeter walls can be described as quite minor. Materials with a higher thermal conductivity coefficient value or significant geometric shapes and points where more heat escapes have a greater effect on reducing the surface temperature. In that case, there is not such a decline that would cause any complications. In all cases, the massive perimeter walls of the buildings show that, despite the reduction in the outside air temperature hygienic criteria on the interior surfaces are still met. The selection of suitable materials and effective building modifications during restoration, without considering additional insulation from the indoor environment, can keep the inner surface temperature of building envelope above the critical temperature for mould growth. It is necessary to look at the entire process of historical buildings restoration from several points of view and assess them using multi-criteria (Ruiz-Jaramillo, 2020).

The photos in Fig. 12 show the building during and after the renovation.

An important aspect was to preserve the appearance of the facade's individual architectural and artistic elements. Views of the windows on the north facade, as well as the adjustment of the detail above the window on the second floor, can be seen in Fig. 13.

5. Conclusions

The purpose of this research was to show the preparation for the renovation and restoration of an old building in the historic center of Kosice, Slovakia, in Central Europe. The building, constructed and currently used for commercial purposes, has undergone several reconstructions. However, the construction characteristics prior to the renovation did not meet the required standards for its intended use. Therefore, an inspection was necessary before commencing the restoration project.

The in-situ test measurement was influenced by several changing factors in both the outdoor and indoor environment. It can be stated that changes in the internal surface temperatures of the perimeter walls under non-stationary conditions were recorded in this manner. Knowledge of the material composition of the perimeter walls could be obtained through surveying, sampling and laboratory measurements, or by means of non-destructive diagnostics. Such a diagnosis can be assisted by the measured temperature trends. The sensors were located on the north and east perimeter walls.

The objective was to determine how the building's envelope walls would behave at low temperatures below zero. This was to demonstrate whether, after restoration, internal surface temperatures would not fall below the critical temperature for mould growth (hygienic criterion).

The temperature of the inner surface fell below the "hygienic criterion" only at a few points, particularly in the place of the Romanesque stone slabs on the windowsills of the northern perimeter wall. Considering the measurement, it can be stated that there are no significant differences in the recorded surface temperatures in places above and below the window ledge (the northern envelope of the building). This fact can be explained by the extensive profiling of the window sill resulting in varying cooling effects on the specific detail oriented towards the north. The existence of a window lintel above the window opening is assumed, although the composition of the lintel is not fully known. It is evident that the lintel above the window has different thermo-physical parameters compared to the material of the external wall. These facts will greatly help in deciding on the method of restoration of the building.

In general, it can be said that the restoration of a building designated as a cultural monument is a unique and highly individual process. Past attempts to provide universal advice and recommendations has often resulted in the destruction of individual qualities of monuments. This trend has contributed to the senseless standardisation of appearance, and thus to the denial of the most precious means of expression, which are supposed to document the diversity and variety of their long-term development. Preserving, and protecting architectural form are primary concerns within the city monument reserve, and functions must adapt to the given form as required by the monument law, which is a legal norm at the level of modern European legislation. Otherwise, instead of restoration, the historic architecture is rebuilt, leading to the partial or complete destruction of the original, along with its irreplaceable expressive values.

In terms of architectural and urban planning, this primarily involves a process of preparation, which represents research and design work-the creative intervention of the architect in the historic architecture, the historical environment, based on comprehensive scientific knowledge. In addition to the personality of the designer and his or her creative invention, close cooperation with representatives of all participating professions is a necessary condition. The Monuments Act specifies that an object may be subject to protection due to preserved values, and that the conditions of protection must be in accordance with scientific knowledge.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This paper was elaborated with the financial support of the research project VEGA 1/0626/22 of the Scientific Grant Agency, the Ministry of Education, Science, Research, and Sport of the Slovak Republic and the Slovak Academy of Sciences.

Sidebar

Institute of Architectural Engineering, Faculty of Civil Engineering, Technical University of Kosice, Kosice, Slovakia

Received 26 January 2024; received in revised form 26 March 2024; accepted 21 April 2024

Footnote

* Corresponding author. E-mail address: [email protected] (D. Katunsky). Peer review under responsibility of Southeast University.

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