Energy-efficient building materials for Arctic conditions as a criterion for "green building"

. The article presents the results of the analysis of the category "building materials" as one of the criteria for buildings environmental certification. The research aims to study one of the categories of "green" certification systems - environmental friendliness and energy efficiency of materials used in construction. The requirements for building materials in international and national rating systems of environmental certification of buildings are considered. Particular attention is paid to determining the most significant characteristics and parameters of building materials as a criterion for "green" construction in the Arctic territories. The use of energy-efficient "green" materials is considered on the example of model objects built in the territories of two northern regions of Russia - in the Murmansk region (Murmansk) and in the Republic of Karelia (Petrozavodsk).


Introduction
Currently, green building as an approach is gaining special relevance. The green building trend finds its confirmation not only in Europe, USA, Canada, etc., but also in Russia. "Green" terminology ("green" buildings, "green" architecture, "green" technologies, "green" construction) is increasingly used in all spheres of human activity. Green building refers to the use of resource efficient and environmentally responsible processes in design, construction and operation to ensure the building sustainability throughout its life cycle. As a theory, green building is based on the concept of sustainable development. Climate change is one of the most important international problems of the 21st century and encompasses all aspects of sustainable development of the entire world community [1].
The Arctic is one of the climate-forming and most fragile ecological systems of our planet. The environmental problems of the Arctic zone are of a global, worldwide nature. At the same time, environmental aspects are starting to play an increasingly important role in the construction industry. Due to the growth in the development of the construction industry, the negative impact on nature is increasing, especially for cities and large agglomerations [2]. Therefore, the approach to cities and settlements development, taking into account the concept of sustainable development, is most relevant specifically for the Arctic regions [3]. On the other hand, the construction of new and the operation of old buildings, taking into account the concept of "green" building, will increase the attractiveness and competitiveness of the Arctic territories [4].
In recent decades, significant efforts have been made to reduce the energy consumption required during the building operation phase (energy required for heating, cooling, ventilation, lighting, water heating and appliance operation). At the same time, the use of more efficient materials and technical solutions in newly constructed buildings has led to an improvement in energy performance throughout their entire service life. The use of "green" building materials is an important criterion for rating a building and plays a key role in achieving the goal of "green" building. Traditionally, building materials are selected based on functional, technical and economic requirements. The design of "green" buildings must be carried out using environmentally friendly and efficient materials with adequate or better performance than traditional building materials. Using eco-friendly building materials can be the fastest way to integrate sustainability into buildings.

Materials and methods
The UN Concept for Sustainable Urban Development provides for the formation of new approaches to the construction and communal and engineering infrastructure creation. The basis of the concept assumes widespread use in their design, construction and operation of environmentally friendly, resource-saving and energy-efficient solutions, technologies and materials. To effectively implement this task, the most modern tools are needed. One of the tools of "green" construction is "green" certification -a systematic approach to assessing a building in terms of environmental safety, energy efficiency and impact on its users and the environment.
At the moment, the most developed and widespread in the world are international and national systems of standards -BREEAM ( [3,5,6]. In many developed countries, taking into account environmental standards is a prerequisite for assessing the quality of an object.
Domestic rating systems have been developed in Russia -NOSTROY 2.35.4-2011, GOST R 54964-2012, RUSO, GREEN ZOOM. Currently, "green" certification of buildings in Russia is not mandatory [7,8]. Despite the existence of these developments, many investors and construction organizations are guided by the well-known international systems BREEAM and LEED.
Scoring systems differ from each other, but have a similar structure. Despite the difference in structure and procedures, all systems focus on assessing the same environmental aspects -energy consumption, water consumption reduction, indoor and outdoor environmental quality, use of materials and resources, and operational management of the building. The differences are mainly focused on the importance that each system places on the sampling criteria.
This study examines the criteria for the selection of building materials in accordance with the principles of "green building". The following are considered as criteria that are taken into account in rating systems for assessing green buildings and by which a material can be classified as "green": -Environmental friendliness; -Resource efficiency; 2 E3S Web of Conferences 383, 04075 (2023) https://doi.org/10.1051/e3sconf/202338304075 TT21C-2023 -Energy efficiency; -Production at the territory of use.

Environmental friendliness
Environmentally friendly materials can be called materials that are not only safe and not harmful to humans (during operation they do not emit harmful volatile substances, do not contain toxic or carcinogenic compounds), but have a minimal impact on the environment throughout the entire life cycle (from the extraction of raw materials to disposal). A significant part of the harmful effect does not come from the materials used themselves, but from the process of their production (soil, water, air pollution occurs). The selection of environmentally friendly materials for use in construction activities at the design stage makes it possible to limit the negative impact on the environment and human health [9].
Proof of Environmental friendliness can be obtained through independent research or voluntary environmental certification. There are over 400 green labels and standards in the world today. In international practice, ISO 14024 is widely used. Type I ecolabel means that the product has been officially certified by an independent party and has been analyzed for its impact on the environment and humans throughout the life cycle (LCA), and its minimum impact has been revealed. Most Type I ecolabelling programs are part of the Global Ecolabelling Network (GEN). Among them, such as FSC, European Flower (European Union), Blue Angel (Germany), Nordic Swan (Scandinavian countries) are known.
Russia also has a Type I eco-labeling program recognized by the international expert community -"Leaf of Life". If a Russian product has the ecolabel "Leaf of Life", then its environmental friendliness has been reliably confirmed not only at the Russian level, but also when the goods are exported abroad. Products will be able to receive type I ecolabels of another country under a simplified certification scheme, which will take less time and labor, and will also be more cost-effective. This makes participation in the Leaf of Life program convenient especially for those manufacturers who are focused not only on the Russian, but also on foreign sales markets [10].
The BREEAM standard requires the selection of materials from "responsible" suppliers who apply an environmental management system in their production and whose products are FSC, PEFC, CARES, Eco Reinforcement certified. The use of materials that have an EPD (Environmental Product Declaration) is encouraged. The latest LEED standard reflects the need to use a certain amount of Cradle-to-cradle, REACH and GreenScreen certified materials, FSC (Forest Stewardship council) certified wood, and materials that have EPD (Environment product declaration) and HPD (Health Product Declaration) safety declarations.

Resource efficiency
Resource efficiency is understood as minimizing the amount of resources and energy used for the manufacture of a material due to the following factors: -The use of inartificial (natural) raw materials (flax, basalt, wood, etc.); -The use in the production of alternative renewable energy sources; -The possibility of using in the manufacture of secondary raw materials and recycled materials (metal, cementite, glass, fiberglass, concrete, brick mortar, wood, etc.), as well as production and consumption waste [11]; -The ability to reuse dismantled material or the possibility of its processing (recycling). Taking into account the resource efficiency of materials at the design stage of a construction object leads to the rational and efficient use of the materials themselves, energy for their production, a decrease in the amount of non-recyclable production waste and reducing the producing materials costs and construction costs. Onsite use of recycled or waste materials should account for between 10% and 20% of the total cost of all materials in the project [2].

Energy efficiency
It should be noted that the energy efficiency criteria category is the most significant in international and domestic green building certification systems (BREEAM (UK), LEED (USA), STO NOSSTROY 2.35.4-2011 and GREEN ZOOM (Russia). In turn, the energy efficiency of materials is one of the important criteria for green building, especially in the Arctic. The abruptly changing climate, the presence of permafrost soils, the low outside temperature during the heating period and its long duration require a special approach to the choice of materials in these areas.
Safe operation of buildings and structures from the standpoint of the thermal regime of premises, which contributes to the economical use of energy resources, is due to the careful selection of energy-efficient materials for the building envelope with the best thermal and physical properties. The emergence of innovations in the field of energy-efficient materials and technologies in the construction sector will not only reduce the consumption of energy resources, and thereby increase the energy efficiency of the facility, but also provide comfortable living and working conditions for people.

Production at the territory of use
This criterion reflects the use of locally produced materials for construction. Locally produced materials are materials that (or one component of which) have been mined and processed within a radius of 800 km [2] from the construction site. Traditionally, when choosing materials for construction, preference was given to local materials. Moreover, during the construction of large objects or their complexes, the presence of construction industry enterprises in the construction area was ensured. Using local materials can save up to 40% on transportation costs and reduce greenhouse gas emissions.

Additional criteria for the Northern and Arctic territories
All the above-described criteria for assessing building materials are also relevant for the conditions of the northern and Arctic territories. The following considered criteria can be singled out as particularly important for the Arctic: environmental friendliness, resource efficiency and energy efficiency. In addition to the criteria noted in the well-known systems of "green" certification of buildings, it is proposed to consider two additional, relevant for the conditions of the northern regions: the availability of material in the area of application and the assembly adaptability.

Availability of material in the area of application
The existing production facilities of the construction industry enterprises in the Arctic cannot provide all the range of materials, products and structures necessary for construction. The placement of new production facilities in the Arctic territories can lead to an even more significant deterioration of the ecological situation and additional damage to the ecological system of the Arctic. Therefore, for the conditions of the Arctic, the authors propose, in addition to the criterion "Production at the territory of use" to consider a new criterion -the availability of material in the area of application. This criterion should take into account the availability of material on the construction site during the construction period within a reasonable radius of its transportation and delivery terms. At the same time, the possibility of delivering materials by the most common and all-season modes of transport and the availability of transport infrastructure should be taken into account.

Assembly adaptability
The special and difficult conditions of the northern territories determine a very short favorable period for the production of construction and installation works. By assembly adaptability, the authors understand the convenience of the material during the production of work and the preservation of the standard parameters of the material during transportation and installation, and as a result, the reduction of construction time and the reduction of the need to provide special conditions when working with the material (a certain temperature, humidity, etc.).

Results and discussion
In 2020, on the territory of two northern regions, the Murmansk region and the Republic of Karelia, two identical experimental buildings -laboratories (model buildings) were built [12]. The main purpose of creating model buildings is to research and evaluate the effectiveness of green technologies in northern conditions [13].
The model object is a one-story building with dimensions in plan 12.45x5.5 m (in axes) with a pitched roof with a low slope. The height of the building at the highest part is 4.3 m. The building consists of two square rooms connected by a vestibule (Figure 1). The right and left parts of the building have the same area and the same internal volume.
Wood was taken as the main structural material [14]. For both parts of the building, the structures of the roof, bottom overlap and foundations are the same. The bottom overlap is made of wooden beams and insulated. The total thickness of the bottom overlap is 465 mm, including the thickness of the heat-insulating layer -300 mm. The roof is gable and insulated. The supporting structures of the roof are represented by a system of rafter legs supported by longitudinal walls and a ridge beam. Roof covering material -metal. The total thickness of the roof structure is 450 mm, including the thickness of the insulating layer -350 mm. The structures of the external walls and the technology of their construction are different for the parts of the building [15]. The structures of the walls of the building parts are made according to two different technologies: one part using frame technology [16], the second one using double frame technology. The total thickness of the wall frame structure is 350 mm. The supporting frame is represented by uprights with a section of 50x200 mm, crossbars of the same section and a system of struts. By the frame racks in the horizontal direction, the frame of the cross layer of insulation with a thickness of 50 mm is made. The total thickness of the insulating layer is 250 mm. The average thickness of the wall structure made using the double-log technology is 472 mm. Insulation layer thicknesses -126 mm. To compensate for the possible settling of the insulation, membranes from a wooden plank 25 mm thick are provided in the wall structure.
The enclosing structures are implemented in multi-layer, which is an urgent solution in the field of thermal protection and allows achieving high heat transfer resistance values without increasing the overall thickness of the structure due to effective heat-insulating materials. The thickness of the layers of the enclosing structures was determined by calculation based on the climatic conditions of the city of Murmansk, but taking into account the receipt of higher thermal protection indicators than the normative ones. The main characteristics of structural and heat-insulating materials and enclosing structures of experimental buildings are presented in Table 1. The use of energy-efficient materials, design solutions and technologies made it possible to obtain a general energy efficiency class for the entire building -A + (very high) [17].
Thermal insulation materials for the experimental buildings were selected based on their compliance with the principles of "green" construction [18][19][20]. The cavity insulation between the logs of a double log house is provided by wood shavings and sawdust, which are waste in the production of rounded logs (Figure 2, left). This material is environmentally friendly, and also quite cheap, as it is a production waste. Mineral wool mats produced by the Saint-Gobain Group (trade marks Isover and Izorok) are accepted as the main heat-insulating material of the frame part of the building. ISOROC Super Warm is adopted as the main heat-insulating material of frame walls, insulated roof and bottom overlap (Figure 3). The material is characterized by dimensional stability, increased elasticity and strength, which ensures the stability material in the frame structure. The product has the lowest thermal conductivity coefficient of 0.037 W/(m·°C) in the segment. In the northern wall of the experimental buildings, different thermal insulation materials were used. In the log part, thermal insulation boards AKOTERM FLAX are used, as well as an air gap without insulation ( Figure 2). Thermal insulation boards AKOTERM FLAX are made of natural flax fiber (85%) and polyester fiber binder (15%). The manufacturer of the material declares that due to the unique arrangement of the fibers and the uniformity of the product, the shape and size of the boards are maintained throughout the entire service life. The material is environmentally friendly and does not cause allergic reactions, due to the presence of flax it inhibits the development of bacteria and fungi, does not rot. The thermal conductivity coefficient for this material is 0.038 W/(m·°C).
In the frame part, three variants of heat-insulating materials are used, alternative to the main one. The first option is the AKOTHERM FLAX thermal insulation boards already described above (Figure 4). The second option is ecowool -cellulose heat and sound insulating material (Figure 5), and the third is FLAXAN heat-insulating boards ( Figure 6).   Ecowool consists of 81% of recycled cellulose processed in a special way, 7% of substances that prevent combustion -fire retardants (borax) and 12% of an antiseptic (boric acid). The main advantages of the material are environmental friendliness and a high degree of fire resistance. Ecowool also excludes the appearance of fungi, mold, rodents, insects. The thermal conductivity coefficient of ecowool is 0.036-0.040 W/(m·°C). This material is laid by dry or wet spraying methods, which makes it possible to effectively perform thermal insulation in hard-to-reach places.
Thermal insulation boards produced under the FLAXAN brand are made from seaweed -scum, flax or hemp and polyester as a binder. Due to the fact that the algae is impregnated with sea salts, the material is non-combustible. Natural components provide the material with environmental friendliness. Iodine released from dried sea grass creates unacceptable habitats for rodents and insects. The thermal conductivity of this material is 0.034-0.043 W/(m·°C). Table 2 presents the results of a preliminary assessment of the construction and heatinsulating materials used in the construction according to the previously proposed criteria for the territory under consideration -the Murmansk region and the Republic of Karelia.
In the table, the signs -, +, ± mark the compliance of each material with the proposed criterion: does not correspond, corresponds, and partially corresponds. It should be noted that there is currently no generally accepted assessment methodology for a number of criteria for rating systems for assessing green buildings. Existing systems use qualitative indicators for assessment and comparison, which leads to different results for the same building in different systems. This problem is mentioned in a number of publications on the topic of "green" construction [21] and requires additional research. In the present study, the assessment was carried out on the basis of the authors' understanding of the essence of each of the criteria set out in the Materials and Methods section of this article.
Assembly adaptability ± ± ± ± + + ± ± ± ± + + As can be seen from the data in the Table 2, all basic materials meet the criterion "Environmental friendliness", since they are based on natural raw materials and are safe for humans. However, the above materials do not have certificates and eco-labels, which does not meet the requirements of the international rating assessment of green construction projects. Accordingly, the building will not receive points in the "Materials" category when evaluated. It should also be noted that the products of the Saint-Gobain company under the Isoroc trademark are included in the GREEN BOOK catalog of environmentally friendly materials, which was developed on behalf of the Ministry of Nature and the Government of Russia. Currently, there is a shortage of materials in the Russian Federation that meet the requirements of green standards (there is no published information, appropriate tests of materials are not conducted). According to the authors, this problem deserves close attention, and mechanisms to stimulate producers and consumers, both at the level of the professional community and at the state level, should be created.
According to manufacturers and suppliers, all materials used meet the requirements of resource efficiency. However, the production of mineral wool products requires high energy costs. The question arises in the possibility of re-use or recycling of fibrous plate heat-insulating materials.
For the buildings under consideration, in the case of wall constructive solution in the form of a double log with an air gap, wood, as a heat-insulating material, does not satisfy the criterion "Energy efficiency" for the studied territories.
In the frame structures of experimental buildings, wood is used only as a construction and finishing material. In the construction of a double log house with an air gap, wood is used both as a structural and heat-insulating material. However, the thickness of the dense layer of wood does not meet the regulatory requirements for heat transfer for the conditions of Murmansk and Petrozavodsk. At the same time, wood is the most environmentally friendly material when considered in terms of the "hydrocarbon footprint".
The use of wood shavings and sawdust as a heat-insulating material makes it possible to achieve the standard values of thermal conductivity of a wall made of two logs. Fibrous thermal insulation materials provide higher than standard indicators of energy efficiency of building envelopes.
All used thermal insulation materials have a similar coefficient of thermal conductivity ( Table 1). As part of further research, it is planned to monitor the operation of experimental objects under operating conditions with measuring temperature and humidity in different parts of the multilayer structure. Based on the results of monitoring and data analysis, it will be possible to formulate more accurate conclusions about the energy efficiency of a particular insulation material.
Some of the materials are not produced in the Murmansk region and the Republic of Karelia (all thermal insulation materials, except for ecowool, and for Murmansk -wood). Due to the developed logistics links of the regions under consideration with the areas where most of the production facilities of the construction industry are located, materials are available for purchase using traditional transport schemes and with reasonable delivery times. This criterion meets the requirements of systems for assessing green buildings for accessibility within a radius of 800 km. This is relevant for the Murmansk region and other Arctic territories, in view of the significant distance to the nearest places of production of materials (the distance from Murmansk to St. Petersburg is 1450 km). However, the Arctic territories of the Russian Federation are largely inaccessible, do not have rail and road connections, which is important when developing a logistics delivery scheme. It is necessary to focus not only on the cost of the material itself and its quality, and on the cost of delivery of products.
The assessment of the criterion "assembly adaptability" is based on the factor of reduced terms of construction and assembly works associated with the difficult natural and climatic conditions of the North (low air temperatures in a long winter period, high atmospheric humidity, and abundance of precipitation). During the production of work, wood and wood-based materials require special conditions for transportation, storage and installation. Linen fiber and seaweed board materials have some problems with stacking and cutting.

Conclusions
1. The analysis of the criteria category "Building materials" of green building certification systems has been carried out. As a result of the analysis, four basic criteria were identified that are relevant for the northern and Arctic territories: environmental friendliness, resource efficiency, energy efficiency and production in the area of application.
2. Two additional criteria are proposed: the availability of the material in the area of use and the assembly adaptability of the material. In addition to the criterion "Production in the area of use", the authors proposed the criterion "Availability of material in the area of use", which is relevant for remote northern territories. The additional criterion "Assembly adaptability of the material" takes into account production in difficult climatic conditions and in a short favorable period.
3. The choice of energy efficient and environmentally efficient building materials (table 1) for the design and construction of experimental buildings in the city of Murmansk and in the city of Petrozavodsk has been made. 4. In order to conduct further research on green technologies in the northern and Arctic territories, the construction of two identical experimental laboratory buildings in the city of Murmansk and in the city of Petrozavodsk has been implemented (Figures 1-6).
5. An assessment of the applied construction and heat-insulating materials for compliance with the considered criteria has been carried out ( Table 2). It is concluded that the applied building materials correspond to most of the criteria for "green" construction.