2. Materials and Methods
The object of the research was represented by evaluation parameters of thermal insulation systems that are required by small investors of a one-apartment residential building. The aim of the research was to prove whether these requirements are in accordance with sustainable development and in line with monitoring of the life cycle of the house construction. The one-apartment building is a one-story family house without a residential attic (see
Figure 1 and
Figure 2). The family house is of a medium size category for a family of four. Natural gas is the source of heating. The perimeter walls of the family house are made of Porfix 500 mm × 250 mm × 300 mm blocks. The blocks are made of white autoclaved aerated concrete based on silica sand. The weight of one block is 24 kg. The interior plasters are lime-cement stucco. The external plasters are lime-cement smooth, provided with Baumit facade paint. The façade paint is a diffusion open coloured paint with a microscopically smooth nano-crystalline surface. The mineral paint is water-soluble, highly vapor-permeable and resistant to contamination. The façade paint consists of mineral binders, silicates, mineral fillers, organic binders, colour and white pigments, additives, and water. The windows and exterior doors are plastic. The ceiling of the family house is prefabricated and made of the ceramic Miako system. The Miako system is a system product for ceramic beam ceilings that are composed of ceramic ceiling inserts and ceramic-concrete ceiling beams reinforced with a welded lattice girder. The roofing is made of the concrete Bramac system. The Bramac concrete roofing is made of high-quality raw materials, namely sand, water, Portland cement, and iron oxide pigments. The strengths of the concrete roofing increase over time, which means a guarantee of its long life and functionality.
This study deals with the analysis of the significance of environmental, cost, and technological parameters of selected thermal insulation systems. The analysis was intent to choose an optimal thermal insulation system for the studied family house. The following thermal insulation systems were examined in the analysis: Baumit OPEN System, Knauf SMARTwall, ThermoUm SATSYS technology, Knauf ECOSE
® Technology, and Aerogels’ Spaceloft
® (see
Table 1).
The Baumit OPEN facade insulation boards are made of stabilized expanded polystyrene with reduced flammability. It is the system component of Baumit OPEN external thermal insulation systems. These are highly vapor-permeable white perforated polystyrene insulation boards with good thermal insulation properties, characterized by dimensional and volume stability.
The Knaufinsulation SMARTwall NC1 ETICS includes mineral insulation boards with silicate spray and thermal insulation properties designed for thermal insulation of external walls as part of a contact thermal insulation system for family houses. The product increases the passive fire safety of buildings, absorbs noise from the exterior, and is vapor permeable.
The thermal insulation plaster ThermoUm SATSYS Technology is applicable for plastering brick, aerated concrete, concrete, and other types of bases. It has hydrophobic and air-permeable properties, which help to remove moisture, prevent the formation of mold on the surface of the walls and inside the structure, and create a healthy and safe environment in living spaces. The natural structure of ThermoUm materials ensures sound insulation and actively helps to create an acoustic environment that prevents echoes in the space. The plaster has a low bulk density and a low modulus of elasticity.
Insulation material ECOSE® Technology TP 435 B is made of mineral glass fibers. It is a contactless technology. The material is treated on one side with black non-woven fabric. The use of its thermal insulation properties and sound absorption properties is mainly in lightweight facade claddings, primarily as an insulation of ventilated facades. When applied to a structure, the material is installed with a black non-woven fabric towards the exterior. The black non-woven fabric serves as a thermal insulation material to minimize airflow cooling in the ventilated gap.
ETICS Aerogels’ Spaceloft® Nanotechnology—the aerogel is an exceptionally fine, porous foam structure, comparable to solidified cigarette smoke. The pore size of the structure is so small that the air molecules in the pores become trapped and cannot, to the extent as without foam, transfer kinetic and vibrational energy to each other, which is the essence of diffuse heat flow. In addition to heat conduction, a radiant component is also used here, but this is absorbed by aerogel and its share in the total heat transfer is also significantly smaller.
When deciding which thermal insulation system or product is the best solution, it is often necessary to work with a large number of parameters or criteria. In order to determine the confidence of the regarded parameters, contractor companies providing the construction of thermal insulation systems were addressed. These companies most often encounter small investors’ requirements in regard to thermal insulation. Determining the confidence (the importance of criteria) in the decision-making process is mostly based on the subjective opinion of the evaluator. To reach an objective opinion, we need to involve more independent evaluators in the decision-making process. Using several optimizing methods and a sufficient number of independent valuation experts participating in the decision-making process, it is possible to objectively determine the weights of the importance of individual criteria.
By the pairwise comparison method, it is possible to determine the weights (importance) of individual criteria and then calculate the confidence coefficient of the criteria. A consecutive comparison of the importance of each criterion with all other criteria is the basis of the pairwise comparison method. The importance of the criteria is obtained from the developed questionnaire with paired questions that represent a combination of criteria, which is filled in by the evaluator—an expert in the area of thermal insulation systems.
The pairs of criteria are calculated by the formula:
N—number of pairs of criteria,
m—number of criteria
The questionnaire (
Figure 3) involves the following criteria (see
Table 2):
The determination of the parameters, on the basis of which the selection of the thermal insulation system was carried out, is based on the analysis of small investors’ demands imposed on contractors who are responsible for insulation’s execution on sites. Based on the current awareness and small investors’ demands imposed on contractors, the criteria presented in
Table 2 were defined. The cost of the thermal insulation system was obtained by calculating construction works and materials in the Cenkros plus software. The total construction time of the thermal insulation system was obtained from the schedules that were developed by the MS Project software. The thermal conductivity coefficient λ (W/(m·K)) was determined based on the manufacturer’s technical data sheets. In principle, the lower the coefficient, the better the thermal insulation properties of the insulation material. The coefficient of thermal conductivity is defined as the ability of a material to conduct heat.
The diffusion resistance factor μ (-) is defined as the ability of a material to transmit water vapor by diffusion. It reflects the relative ability of a material to transmit water vapor. It indicates how many times the diffusion resistance of a given substance is greater than an equally thick layer of air at the same temperature. The reaction to fire class is the ability of building materials to withstand the temperatures of ignition, smolder, or combustion. The values of these criteria were determined based on the manufacturer’s technical data sheets (EN 13501-1:2010). The score is presented in
Table 3.
A questionnaire was developed to determine the confidence of individual criteria (see
Figure 3). The questionnaire was filled in by contractors (evaluators). Each evaluator has indicated their preferred order of the submitted parameters. The principle of evaluating the questionnaire is to mark at least one of the pair of criteria that is of the greatest importance to the evaluator. The preferences of individual criteria are written in a table (matrix) of relationships. The confidence coefficient is determined based on the calculation of the partial weights of the different evaluators.
The determination of the criteria confidence was then followed by multi-criteria decision-making with the help of the method of index coefficients, also known as the method of the basic variant. By the method, the partial evaluation of individual criteria was determined through calculating the partial confidence coefficients (Bj). The confidence coefficients were determined by comparing the value of the criterion (parameter) of the evaluated variant with the values of the basic variant. The basic variant is a simulated variant, which contains the theoretically worst or best values of partial weights. In the calculation, two groups of the criteria were distinguished. The cost-type criteria were in the first criteria group. The cost-type criteria were those whose lower values in terms of efficiency were most preferred by the evaluator over higher values. These are the criterion-value-minimizing type. The higher the value of the sub-criterion, the worse the rating. The revenue-type criteria represent the second group of criteria. The revenue-type criteria were those whose higher value in terms of efficiency was most preferred by the evaluator over lower values. These are the criterion-value-maximizing type. The lower the value of the sub-criterion, the worse the rating.
Then, the confidence coefficient of the Bj criteria was calculated. The confidence coefficient is the basic parameter when used in various methods of multi-criteria decision-making. The confidence coefficient of the Bj criteria is determined by the formula:
Bj—the coefficient of the criteria confidence.
Υj—the sum of the partial weights of the criteria assigned to the criterion of all evaluators.
p—the number of evaluators.
The process of the multi-criteria decision-making by the method of index coefficients (the method of the basic variant):
1. The forming of the matrix of variants and criteria—in this case, the variants were different thermal insulation systems designed for thermal insulation of the family houses and the criteria involved the cost of the thermal insulation system per 1 m2, the construction time of the thermal insulation system, the thermal conductivity coefficient (λ), the diffusion resistance factor (μ), and the reaction to fire class.
If some values of the variant criteria were the same when ranking the criteria, the order was determined as the average of the sum of the orders belonging to the identical parameters.
2. Determination of the types of criteria (revenue and cost). Creation of the simulated (basic) variant.
For revenue-type criteria:
where:
zij—the fictive value of the partial criterion of the variant confidence.
hbj—the value of the jth criterion in the fictive (basic) variant.
hij—the real value of the jth criterion in the ith variant.
Bj—the confidence coefficient.
For each variant, the value of relative confidence (
Sj) was determined.
where:
Sj—the total relative value of the sub-criteria of the variants’ confidence.
zij—the fictive value of the sub-criterion of the variant confidence.
During evaluation (Vj) of the confidence variants, the variant with the smallest number of relative confidence came first.
The aim of implementing the multi-criteria decision-making methods was to determine the optimal choice of thermal insulation system for the family house. The variants of thermal insulation system represent the object of the decision-making process. The group of evaluators/contractors who deal with the construction of thermal insulation, the manufacturers of thermal insulation materials, and the sellers of thermal insulation systems and materials were the subject of the decision-making process. In their answers, they followed the preferred parameters of small investors, who they usually encounter in their practice. The method of Fuller’s triangle was applied to evaluate the outputs of the questionnaires. It is a method of pairwise comparison of criteria. Each pair has 1 point. Each criterion gets as many points as were marked by the evaluators. If both criteria were marked in any pair, both criteria get half a point. The trade names of the companies’ evaluators, A–E, are not listed in the study. The authors may provide these names upon request.
4. Discussion and Conclusions
Due to a constant push to reduce energy consumption for the operation of constructions, the investors are led to choose a thermal insulation material to insulate their buildings. When choosing a thermal insulation system, small investors prefer the cheapest variant. The demands on thermal insulation materials are becoming more rigid. There are several research studies [
30,
31,
32] focused mainly on the physical and technical properties of insulation materials in accordance with legislative requirements. The work of Alsayed and Tayeh [
33] deals with an optimization of insulation thickness in buildings’ external walls. The life cycle costing approach was applied in the optimization. For the climatic conditions of Palestine, the optimal insulation thickness (polystyrene and polyurethane) varied between 0.4 and 9 cm. However, unlike our work, constructions were analyzed by a different methodology in their study. The authors examined annual energy savings, which varied between 4 and 8 dollars per m
2 per year (between 4 and 8
$/m
2/year). Similar to our work, Aïssani et al. [
34] and Dombayci et al. [
35] have argued that the performance of an insulated construction depends mainly on the thickness and the properties of the used insulation material, even though the performance is subjected to various uncertainties related, for instance, to the manufacturing process of the material. Liu et al. [
36] have also dealt with reducing the life cycle cost of a building. Their results have demonstrated that the total life cycle cost of an exterior wall using expanded polystyrene as an insulation material is lower than using extruded polystyrene (XPS) as insulation. This indicated that EPS is more economical than XPS. The optimum thickness of XPS was found to be between 0.053 and 0.069 m and the optimum thickness of EPS was found to be between 0.081 and 0.105 m. With respect to the climatic conditions of Slovakia, a comparable thickness of EPS insulation (0.14 m) was examined in our research study. A similar research study was conducted by Norwegian researchers [
37]. Various combinations of insulation thicknesses were assessed to identify which combination is most efficient in lowering lifetime carbon emissions. Vrbka and Tichá [
38] analyzed the costs of thermal insulation systems to reduce the energy consumption of family houses. In their research, calculation methodologies to determine construction costs were used in the form of itemized budgets. The methodology of construction costs estimation with the help of itemized budgets was also applied in our study.
The life cycle costs (LCC) of buildings were also examined by other authors. Plebankiewicz et al. [
39] have proposed a model that allows the investor to compare buildings in terms of the LCC already in the early stages of planning a construction project. According to our study, in the initial stage of a construction project, it is possible to replace the thermal insulation system and, thus, it is possible to change the costs of the whole life cycle of a building. In this way, the phase of the building material production can be considered. We can say that they only monitored construction cost when trying to reach energy savings during the use phase of the building. They did not consider the production of some insulating materials, such as, for example, polystyrene, which can negatively impact the environment for many decades. However, when choosing another, mostly more expensive thermal insulation material, the environment could be less burdened. The possibility of such a selection requires the existence of a database of building materials, which would list the amount of emissions that are emitted into nature and the environment during the production of the material. An example of such a database is the international Environmental Product Declaration (EPD) system. So far, Slovak legislation does not require the entry of manufacturers of building materials in the database. Even on its own initiative, there is no Slovak company in the EPD database, which reflects the awareness of the calculation of environmental costs of building materials in Slovakia. Of course, political will and legislation are needed to start the process in order to meet the requirements of the Paris Climate Agreement, to which the Slovak Republic has also committed itself.
The authors of the article consider it especially important not only to raise awareness about the environmental costs of building materials but also to introduce the need to calculate the environmental costs into the legislation of the Slovak Republic. It is necessary to consider the entire life cycle of the construction and calculate the costs of the entire life cycle of the construction. Currently, only the procurement cost of construction is considered. It is necessary to evoke the responsibility of investors for the constructions provided by them. This involves responsibility for the sustainable extraction of raw materials, for the building materials used, for sustainable construction, for the sustainable operation of the building, and also involves the responsibility for the demolition of constructions and the recycling of construction waste at the end of the building life cycle. The investor must therefore decide on a more environmentally friendly solution. Ultimately, this will not only provide the investor with a reduction in the environmental cost but also a reduction in the cost of the construction life cycle. It is also one of the ways to achieve carbon neutrality, reduce energy consumption and the generation of construction waste on Earth, and stop global warming.
In our work, we examined small investors’ demands on thermal insulation systems to insulate a family house. It was found that the lowest cost and the lowest coefficient of thermal conductivity are the most important requests of small investors when choosing an optimal solution for a thermal insulation system. Furthermore, it was found that small investors are not interested in the degree of environmental impact of the material production in the factory. The environmental cost of building materials, which depends on the carbon footprint from the initial origin of the materials, are not fully included in the price of thermal insulation materials. It is common for environmentally friendly materials (also known as biomaterials) to be more expensive than materials that are more harmful to the environment. This situation should be changed, even if some changes in legislation are needed. In this way, it will be possible to implement measures aimed at achieving carbon neutrality.
Our work tried to point out the need to deal with the monitoring of emissions already in the production phase of thermal insulation materials. In addition to efforts to reduce emissions in the phase of use of an insulated building, this is one of ways to move towards the desired carbon neutrality by 2050.