Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2022.38.0222 Acta Polytechnica CTU Proceedings 38:222–227, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague NATURAL MATERIALS IN BUILDING CONSTRUCTION – ANNUAL EVALUATION Daniela Michálková∗, Pavol Ďurica University of Žilina, Faculty of Civil Engineering, Department of Building Engineering and Urban Planning, Univerzitná 8215/1, 010 26 Žilina, Slovakia ∗ corresponding author: daniela.michalkova@uniza.sk Abstract. The construction industry’s focus on a low-carbon economy will result in the need for a deeper examination of natural-based building materials. From an environmental point of view, the benefits of these materials are undeniable. However, it is necessary to consider their shortcomings in other areas of design in terms of building thermal engineering. This article observes and evaluates a wall designed for a wooden building with almost zero energy demand in year-round operation and subsequent assessment in confrontation with a different composition, seemingly more advantageous in thermal resistance and humidity regime. These assemblies are under long-term examination within the pavilion research of the authors’ workplace, in laboratory conditions from the interior side. At the same time, they are exposed to the realistic boundary conditions of the external environment. The paper includes an environmental assessment of two compositions, variating in the used material. The research shows that the wall composition of natural materials is more advantageous from an ecological perspective and can also show favourable effects in terms of temperature and relative humidity regulation. Keywords: Timber-framed, natural building materials, temperature, relative humidity, environmental assessment. 1. Introduction The acute need to improve the environment is an in- creasingly trending topic. Sustainable development includes many issues, among others, improvement of the building industry [1]. In order to maintain liveable conditions of the earth, it is necessary to reduce the use of materials with great primary energy demand [2]. According to the Paris agreement [3], the United Nations – 191 countries, which signed the document – are bound to keep the global temperature rise this century below 2 °C and report every five years their actions to ensure the goal. The harmonised requirements for construction prod- ucts summarises the EU Regulation No. 305/2011 of the European Parliament and Council [4], which significantly supports the use of raw and secondary materials in the building industry. At the same time, the requirements of current legis- lation regarding the thermal protection of buildings [5] are equally important. 2. Experimental wall samples This article aims to present two different wall assem- blies containing various materials. Both face south orientation with 15 ° inclinations to the west, and both are exposed to the natural exterior climate, measured on the laboratory roof. The interior space uses air con- ditioning, and its’ temperature and relative humidity are appropriately measured. The research contains overall ten wall samples. All of them are under long-term investigation to moni- tor the temperature and relative humidity within the timber-framed multi-layered constructions. The moni- toring is in three high levels – 0.5 m under the ceiling, in the middle of the structure height, and 0.5 m above the floor – in all material interfaces. In this paper, we present values in the middle of structures’ height, apart from the interface between phenolic foam and OSB in S1, bearing in mind that we would have noth- ing to compare these values to in wall S1. Used are NTC thermistors with the accuracy of ± 0.2 °C for temperature and capacity probes with the precision of ± 2 % for the relative humidity. The first wall in this paper, marked as S1 (south 1), is the only one with solely natural materials. The second, marked as S2 (south 2), was chosen for com- parison, as it is the most similar to the first assembly. Both these wall constructions are diffusely open, en- abling air and water penetration and thereby reducing the risk of fungi and mould settling. Wall S1 in Figure 1 solely consists of timber frame, timber log profiles from exterior and interior and sheep wool within. S2 has the same exterior layer, followed by basalt fibre thermal insulation Isover Granulate, phenolic foam insulation Kingspan Kooltherm K5, fin- ished by OSB. The probes are in three depths within the wall: inside under the log profile, in the middle of thermal insulation, between wool and interior log pro- file (S1), and between Isover Granulate and Kingspan Kooltherm (S2). Table 1 comprises the materials of both wall assem- blies with tier main physical characteristics and envi- ronmental indicators. Among them is d – thickness, 222 https://doi.org/10.14311/APP.2022.38.0222 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 38/2022 Natural materials in building construction – annual evaluation Figure 1. Left South wall 1 (S1), right South wall 2 (S2) – layers, probes placement. Material d λ µ ρ c GW P P EI AP [m] [ W m3·K ] [-] [kg/m3] [ J kg·K ] [CO2eq/kg] [MJ/kg] [SO2eq/kg] Timber profile [6] 0.068 0.180 157 400 2510 0.109 1.959 0.00128 Sheep wool [7] 0.220 0.042 1.5 16 1720 0.537 19.324 0.00463 Basalt fibre TI [6] 0.220 0.040 1 50 1020 0.346 21.363 0.01413 Phenolic foam TI [8] 0.040 0.021 35 35 1400 3.821 96.515 0.01742 OSB [6] 0.012 0.130 50 650 1700 0.481 12.506 0.00210 Table 1. Layer materials of both assemblies and their main characteristics. Figure 2. S1 environmental evaluation (baubook.at). λ – thermal conductivity factor, µ – water vapour diffusion factor, ρ – bulk density, c – specific heat capacity, GW P – global warming potential, P EI – primary energy intensity, and AP – acidification po- tential, listed. TI stands for thermal insulation. Figure 3. S2 environmental evaluation (baubook.at). 3. Environmental assessment The environmental benefits of the first wall are unde- niable. On the other hand, the second wall consists of more durable materials and therefore may balance the negatives. Thus rose the need to establish the environmental impact of both structures. The assess- ment stems from the Baubook website [9], which is 223 Daniela Michálková, Pavol Ďurica Acta Polytechnica CTU Proceedings Figure 4. Comparison of the temperature in the winter period. Figure 5. Comparison of the relative humidity in the winter period. an online platform that promotes sustainable building design. This website enables the evaluation of the building structures in terms of the OI – ecology in- dex (Ökoindex) [10] that considers the environmental indicators such as GW P , AP , and P EI. For compar- ison, the standard value for common wall assemblies is 70 pts/m2 [11]. The results of the environmental assessment are in Figure 2 and Figure 3. For comparison, the U -value (heat transfer coefficient) is according to STN EN ISO 6946 [12] 0.196 W/(m2 · K) for S1 and 0.145 W/(m2 · K) for S2, calculated as inhomogeneous wall structure. As shown, the wall assembly marked as S1 consist- ing of timber log profiles and sheep wool is classified as A++ according to OI-class, with ∆OI3 value 6 pts/m2. The structure S2 of timber log profile, basalt fibre in- sulation, phenolic foam insulation and oriented strand board reached value 38 pts/m2 and thus fell to the A+ class. 4. Temperature and Relative Humidity The temperature and relative humidity, measured in three depths of the wall (Figure 1), provided large datasets throughout the year. To simplify the com- parison, these quantities are in this paper divided into three sections – winter period from 20th January to 2nd February, spring period from 19th March to 1st April, and summer period from 18th June to 1st July. Dotted lines present the temperature and relative hu- midity of exterior air. Interior climate was set to 20 °C temperature and 50 % relative humidity. The values in placement S1.1 or S2.1 are further referred to as the interior. In this case, we use this term only to simplify the text slightly. However, we would like to emphasise the layers between the probes placement and the interior, which we are aware of. 4.1. Winter Period The graph in Figure 4 shows the temperature in both structures during two weeks of winter. The yellow dotted line represents the exterior air temperature. The other six lines stand for the temperature, whereas the different placements have different colours. The wall assemblies are distinguished by colour shade. Although the temperature of S1 is from the exte- rior and in the middle of the wall lower than in S2, it reaches almost 5 °C higher values from the inte- rior. That is naturally caused by the phenolic foam from the interior in the case of S2. However, S2 is ex- 224 vol. 38/2022 Natural materials in building construction – annual evaluation Figure 6. Comparison of the temperature in the spring period. Figure 7. Comparison of the relative humidity in the spring period. pected to reach a lower temperature under the exterior cladding due to the higher thermal performance. An- other investigation consequently followed this analysis. Unfortunately, we found out that in S2 was created an air cavity, causing an additional thermal bridge. Significant is the alignment during the days where the amplitude of exterior temperature was smaller. The temperature these days was in the middle almost identical. Figure 5 displays relative humidity in the same pe- riod. The walls and probe placement is distinguished the same way as in the case of temperature. The regulation of relative humidity is, in the case of S1, very significant. The difference between exterior and interior relative humidity is almost 50 %, whereas in S2, only 20 %. It may sound unreasonable, but the explanation behind this statement is the following. Both assemblies are under constant interior boundary conditions, which means we can see only the influence of exterior climate. Although S1 reaches higher rela- tive humidity from the outside, it meets the values of S2 relative humidity already in the middle of the insu- lation layer. The sheep wool was able to further lower the relative humidity to circa 30 %, whereas in basalt fibre, the value is around 40–50 %. This is the reason why we claim that sheep wool has the ability to regu- late relative humidity better. The relative humidity in the middle is very similar in both assemblies. The variations occur under the outside and inside layers of both. Also interesting is the course of the humidity itself. The wall S1 reached steadier values throughout the whole period. 4.2. Spring Period To represent the spring period, we have selected two weeks from 19th March to 1st April. Figure 6 shows the temperature comparison. The daily amplitude is naturally more significant. From the outside, the solar impact on the temperature of the exterior layer is evident, where the temperature in the walls is 15 °C higher than the surrounding air temperature. Other than that, the course of temperature is similar to the winter period, where the middle temperature is almost identical, and the interior temperature differs the most. Figure 7 presents the relative humidity. The differ- ence between exterior and interior humidity is here not so significant and gets even smaller towards the end of selected weeks. However, the internal relative humidity is again lower in the case of S1 compared to the wall S2, creating a difference of nearly 10 %. 225 Daniela Michálková, Pavol Ďurica Acta Polytechnica CTU Proceedings Figure 8. Comparison of the temperature in the summer period. Figure 9. Comparison of the relative humidity in the summer period. 4.3. Summer Period The summer period is represented by 14 days from 18th June to 1st July. As expected, the temperature amplitude is large, with a maximum variance of 24 °C. It is displayed in Figure 8, where a noticeable temper- ature shift is apparent, in some cases reaching 6 hours. According to Figure 8, wall S1 is capable of higher temperature regulation. To support this statement, notice that the temperature from the outside is, in its case, higher than in S2. In contrast, already in the middle of thermal insulation is vice versa, where the S1 temperature is 3 °C lower than the S2. Figure 9 shows the course of relative humidity dur- ing the summer period. In this case, the difference is foremost in the interior layer, caused by the air relative humidity rise due to some technical difficulties with the air conditioning. However, the relative humidity in the middle of both walls is relatively consistent, varying from 50 to 60 %. 5. Conclusion Although both wall assemblies appear very similar, their difference is rather significant. The first struc- ture consists solely of natural materials with minor adjustments to enable their use in buildings. The second wall uses a combination of natural materials – timber frame, exterior timber log profile, and oriented strand board – and synthetic materials, such as basalt fibre thermal insulation and phenolic foam to improve its thermal resistance. Nevertheless, the difference is not significant enough to balance the environmental impact. As stated in the Section 3 (Environmental assess- ment), both structures fall into the highest categories in terms of Ecoindex. However, wall S2 requires al- most double primary energy in comparison with S1. Moreover, the acidification and global warming po- tential are also double. In terms of ∆OI3 is for wall S2 is more than six times greater – 38 pts/m2 versus 6 pts/m2 for S1. From the perspective of used materials, wall S2 is expected to show better temperature and relative humidity results. The opposite turned out to be the case, where the first assembly showed its capability of not only competing with S2 in terms of thermal performance but, in some cases, even outstanding it. Wall S1 provides more significant temperature decre- ment towards the interior, obvious foremost in the summer period. The regulation of relative humidity within S1 was in some cases 30 % greater opposite to 226 vol. 38/2022 Natural materials in building construction – annual evaluation wall S2. However, it is needless to say that neither of the wall assemblies showed relative humidity values that could initialise the growth of moulds and fungi or cause material degradation. The main conclusion of this paper is not to under- estimate such wall assemblies, which can prove their worth not only in terms of environmental sustainabil- ity but also in terms of overall performance. Future research could contribute by numerical simulation of both wall structures within an actual building and deeper evaluation from an LCA point of view. Acknowledgements The research of this paper was enabled through the VEGA project Nr. 1/0673/20 Theoretical and experimental analy- sis of energy effective and environmentally friendly building envelopes. References [1] D. A. Suhamad, S. P. Martana. Sustainable building materials. IOP Conference Series: Materials Science and Engineering 879(1):012146, 2020. https://doi.org/10.1088/1757-899x/879/1/012146 [2] W. S. E. Ismaeel. Material selection for sustainable buildings. In Conference paper ARCOM 2021. 2021. [3] United Nations. Paris Agreement to the United Nations Framework Convention on Climate Change, 2015. [2022-02-28]. https://unfccc.int/sites/ default/files/english_paris_agreement.pdf [4] European Union. Regulation (EU) No 305/2011 of the European Parliament and of the Council of 9 March 2011 laying down harmonised conditions for the marketing of construction products and repealing Council Directive 89/106/EEC. [2022-02-28]. http://data.europa.eu/eli/reg/2011/305/oj [5] STN 73 0540-2+Z1+Z2 Thermal protection of buildings. Thermal performance of buildings and components. Part 2: Functional requirements, 2019. [6] Inštitút pre energeticky pasívne domy. Ekologické materiály pre energeticky pasívne domy (EPD), 2020. [2022-02-28]. https://ozartur.sk/wp- content/uploads/2020/08/iEPD-materialy.pdf [7] U-values for sheep wool insulation, 2014. [2022-02-28]. http://www.isolena.cz/wp-content/uploads/0259_ ISO17_Architektenordner_2_U-Werte- Produktdatenbl%C3%A4tter- Akustikd%C3%A4mmung_CZ_III.pdf [8] Kingspan. Environmental product declaration – Kingspan Kooltherm K5, 2019. [2022-02-28]. https://www.kingspan.com/pl/pl- pl/produkty/izolacje/pliki-do- pobrania/certyfikaty/epd-kooltherm-k5 [9] Baubook component calculator, 2018. [2022-02-28]. https://www.baubook.at/BTR/ [10] Oekoindex component evaluation, guideline for the ecological evaluation of component constructions by means of eco-index v1.4„ Energy Institute Vorarlberg, Dornbirn. [11] A. Iringová. Design of envelopes for timber buildings in terms of sustainable development in the low-energy construction. IOP Conference Series: Materials Science and Engineering 415:012010, 2018. https://doi.org/10.1088/1757-899x/415/1/012010 [12] STN EN ISO 6946 Building components and building elements. Thermal resistance and thermal transmittance. Calculation methods, 2001. 227 https://doi.org/10.1088/1757-899x/879/1/012146 https://unfccc.int/sites/default/files/english_paris_agreement.pdf https://unfccc.int/sites/default/files/english_paris_agreement.pdf http://data.europa.eu/eli/reg/2011/305/oj https://ozartur.sk/wp-content/uploads/2020/08/iEPD-materialy.pdf https://ozartur.sk/wp-content/uploads/2020/08/iEPD-materialy.pdf http://www.isolena.cz/wp-content/uploads/0259_ISO17_Architektenordner_2_U-Werte-Produktdatenbl%C3%A4tter-Akustikd%C3%A4mmung_CZ_III.pdf http://www.isolena.cz/wp-content/uploads/0259_ISO17_Architektenordner_2_U-Werte-Produktdatenbl%C3%A4tter-Akustikd%C3%A4mmung_CZ_III.pdf http://www.isolena.cz/wp-content/uploads/0259_ISO17_Architektenordner_2_U-Werte-Produktdatenbl%C3%A4tter-Akustikd%C3%A4mmung_CZ_III.pdf http://www.isolena.cz/wp-content/uploads/0259_ISO17_Architektenordner_2_U-Werte-Produktdatenbl%C3%A4tter-Akustikd%C3%A4mmung_CZ_III.pdf https://www.kingspan.com/pl/pl-pl/produkty/izolacje/pliki-do-pobrania/certyfikaty/epd-kooltherm-k5 https://www.kingspan.com/pl/pl-pl/produkty/izolacje/pliki-do-pobrania/certyfikaty/epd-kooltherm-k5 https://www.kingspan.com/pl/pl-pl/produkty/izolacje/pliki-do-pobrania/certyfikaty/epd-kooltherm-k5 https://www.baubook.at/BTR/ https://doi.org/10.1088/1757-899x/415/1/012010 Acta Polytechnica CTU Proceedings 38:222–227, 2022 1 Introduction 2 Experimental wall samples 3 Environmental assessment 4 Temperature and Relative Humidity 4.1 Winter Period 4.2 Spring Period 4.3 Summer Period 5 Conclusion Acknowledgements References