Thermal Insulation of Agricultural Buildings Using Different Biomass Materials

Abstract

The main goal of the article is to present the effectiveness of biomass as a thermal insulator and estimate the global potential for using biomass, considering the perspective of sustainable development and improving energy efficiency in agricultural building construction. The article presents two types of piggery construction: one using typical materials like concrete and the other using biomass-based materials. The evaluation is based on carbon footprint and embodied energy indicators. The model calculations developed in this article may be used in the future for life cycle assessment (LCA) analyses of specific construction solutions for rural livestock buildings. Two model variants for constructing a pigsty with different insulating materials were compared. The TB (Traditional Building) variant consisted of layers of (AAC) Autoclaved Aerated Concrete, glass wool, and brick. The second model variant, HB (Hempcrete Building), was made of concrete blocks with the addition of industrial hemp (Cannabis sativa L.) shives. Regarding footprint evaluation, bio-based materials often have a net-negative carbon footprint due to the sequestration effect. The results showed a significant difference in the carbon footprint of both TB and HB solutions—the carbon footprint of the HB variant was only 9.02% of that of the TB variant. The insulation properties of hempcrete were also compared to those of the most frequently used insulating materials in construction, such as glass wool and rock wool. The novelty of the study lies in analyzing the potential use of biomass for thermal insulation in livestock buildings, considering various raw materials, including their industrial properties and the ecological benefits resulting from their implementation. In addition, the authors focused on biomass thermal insulation from the perspective of sustainable development and improving energy efficiency in building construction. Our evaluation and selection of the best solutions are based on the indicators of embodied energy and carbon footprint.

1. Introduction

In the context of global challenges related to climate change and sustainable development, energy-efficient construction is gaining increasing importance. A key aspect of this is the effective thermal insulation of buildings, which helps reduce energy consumption and greenhouse gas emissions. Traditional insulation materials, such as mineral wool and polyurethane foam, while effective, are associated with a high carbon footprint and the generation of waste that is difficult to dispose of. A report on the global thermal insulation materials market forecasts that, by 2029, the market value will increase to USD 35.6 billion, up from the current USD 28.6 billion [1].

Buildings account for 40% of global energy consumption and are responsible for 30% of total carbon dioxide emissions [2], mainly due to the energy used for air cooling, air conditioning, and heating. According to the report [2], the share of global energy consumption by the buildings and construction industry is approximately 36%. Portland cement, a commonly used building material, contributes to the emission of 1 ton of CO₂ for every ton of cement produced [3]. In 2022, 4.12 billion tons of cement were used globally [3], and the market is forecasted to grow significantly to 6.1 billion tons by 2025 [4]. Prakash [4] emphasized the advantages of using plant-based natural fibers in construction, especially in rural areas, including their renewable origin, global availability, low cost, limited energy requirements for production, and biodegradability.

In recent years, there has been growing interest in alternative, ecological solutions that can replace, either partially or entirely, not only the aforementioned cement [4,5] but also conventional insulation materials. Efforts are underway to reduce greenhouse gas emissions through research into new materials [6,7,8], such as biochar, which can be used to make bricks and insulation materials [8].

Plant-based materials are characterized by low embodied energy [9,10] and cost-effective structural systems suitable for developing economies. In addition, construction waste from plant-based materials is biodegradable, which helps lower the overall carbon footprint [10] compared to traditional materials like stone wool and glass wool, which have high embodied energy and contribute significantly to the global warming potential (GWP) during production [9,11,12].

The distribution of insulation materials used in construction worldwide is presented in Figure 1.

Traditional organic materials include stone wool, rock wool, glass wool, and glass foam. Stone wool is made from volcanic rocks, such as basalt and dolomite. Among organic materials derived from fossil fuels are polystyrene and fiberglass, while plant-derived or animal-derived organic materials which are the most widely represented, include wood fiber, cotton, cellulose, flax, hemp, and sheep wool [13,14]. Insulation materials can be made from either inorganic or organic materials [15]. Polystyrene has two variants: extruded polystyrene (XPS) and expanded polystyrene (EPS) [16,17]. There are also some innovative materials as aerogels, textile fibre, and others.

Organic materials such as cotton, hemp, straw, and sheep wool do not yet have a harmonized standard (hEN) or European Technical Assessment (ETA) [18]. Anyway, biomass, due to its renewable source, availability, and thermal properties, is becoming a promising raw material for producing thermal insulation materials. Biomass-based insulation materials can be used in almost all types of buildings. Anyway, straw or wood fiber may struggle to meet stringent fire resistance requirements in some countries. Hempcrete materials are not suitable for multi-level buildings like modern sky-scrapers because of a high compressive strength demand.

One factor that must be considered in the management of biomass intended for thermal insulation production is the heating of the stored material. Wood waste and energy willow material are stored in a finely divided form with a high moisture content—approximately 50% of the dry matter. It is important to control the storage of biological materials such as wood, field crop stalks, cereal grains, hemp, and green mass from hop production. When managing large quantities of bulk materials for storage, it is important to focus on proper storage conditions for their use in the thermal insulation of agricultural buildings.

The storage of particulate wood-chip material is associated with the risk of increased temperature, decomposition, and the development of harmful bacterial strains, which can lead to a loss of dry matter. To prevent the loss of dry mass during storage, it is crucial to understand the basic characteristics of process parameters, including the relationship between wood moisture content and relative humidity as ambient temperature changes. Another important element of this process is identifying and determining the equilibrium between the material’s moisture content and the relative humidity of the air at a constant ambient temperature. These data are essential for controlling the storage, drying, and calorific value of biological hygroscopic materials such as wood, field crop stalks, cereal grains, and green mass from hop production. To more accurately evaluate the process, laboratory-scale tests are necessary to derive the appropriate dependencies for real-world conditions [12]. Findings from Pomada et al. (2024) indicated that improper storage conditions can adversely affect the thermal properties of insulation materials [19].

Plant fibers (hemp, jute, miscanthus, willow, etc.) are used not only as a substrate for biogas production [20,21] but also in various other industry sectors. Hemp residues, in addition to being used for the production of briquettes and pellets, have applications in packaging, the automotive industry, and construction [22]. Various types of biomass, including agricultural, forestry, or fast-growing plants (e.g., reed grass, energy willow), can be used to produce sustainable insulation materials. One such plant is industrial hemp, which is used in the production of hempcrete, hemp blocks, conglomerates, panels of different densities, and plasters, due to its excellent thermal insulation properties [22,23,24]. As of August 29, 2024, the total area of fiber hemp cultivation in Poland, as reported to the KOWR (National Center for Agricultural Support) in applications for the registration of producers in the fiber hemp registry, was 1358 ha [25]. Up to 15 tons of dry biomass can be obtained from 1 ha of fiber hemp, of which 6.7 tons is cellulose [26].

The world production of industrial hemp cultivated specifically for fiber purposes totals 275,000 ha [27]. The leading producers of industrial hemp are China, the United States, Canada, France, and Germany. In 2022, the production of fiber hemp in the EU totaled 33,020 ha [28]. Recently, hemp production in the EU increased from 97,130 tons to 179,020 tons, marking an 84% increase. France is the largest producer of hemp in the EU, accounting for more than 60% of the EU’s total harvest. Hemp fibers are used in construction materials such as hemp lightweight concrete and hemp panels due to their light weight, strength, and excellent insulation properties [29].

Hemp products can be utilized in animal building construction in some varieties. Concerning the hempcrete structure, we can say that this is a mixture of woody hemp core and lime (1:2 ratio) that is placed directly into the formwork on site, similar to the process used in standard concrete casting. This material is used to build partition walls, ensuring thermal acoustic insulation and high breathability. The lime used is hydrated lime, and the wooden structure supports the wall. The size of hemp seeds used ranges from 6 to 15 mm. This material is used to build non-load-bearing walls, ensuring thermal acoustic insulation and high breathability. The lime used is hydrated lime and the wooden structure supports the wall.

The second type of hemp-based building material is hemp blocks. These are prefabricated elements made of lime and natural or mineralized hemp-based mixtures, with grain sizes ranging from 6 to 15 mm [30].

They are used to build walls, with hydraulic lime as a binder and the possible addition of secondary binders. Hemp blocks are very convenient both for transporting them to the construction site and when constructing walls.

A third type of hemp-based building material is conglomerate, a compound of the woody core of hemp and lime, used to insulate vertical structures. The lime used is hydrated or aerated with other natural additives. It provides thermal and acoustic insulation and high breathability. The lime used is hydrated or aerated along with other natural additives. High-density panels are self-supporting insulating panels consisting of a woody-hemp core mixed with natural binders or glues/resins (sometimes containing raw earth). Low/medium density panels are made by compressing hemp fiber mixed with binders (usually cornstarch) at a variable percentage from 10% to 15%, sometimes treated with flame inhibitors such as ammonium salts. High-density panels are self-supporting insulating panels consisting of a woody-hemp core mixed with natural binders or glues/resins (sometimes containing raw earth). The panel system is used to create various types of internal and external structures, such as recesses or suspended ceilings. The construction solution used ensures thermal and acoustic insulation as well as high breathability.

The final finishing construction material is plaster, which comes in three types. They are made by mixing the woody core of hemp with lime (hydrated or air), with the size of the hemp grains ranging from 3 to 6 mm, 1 to 3 mm, and less than 1 mm, respectively. In the third type of solution, you can add marble dust, hemp oil, or cellulose. A characteristic feature of the hempcrete composite mix is its relatively low strength; however, its advantage lies in its excellent thermal insulation properties [30]. The type of binder does not significantly affect the compressive strength, as these values do not exceed 0.4 MPa for each binder type in mixtures with an optimal composition, as shown by research [31]. However, the binder used does influence the thermal conductivity coefficient [30]. Thermal insulation materials create a barrier that protects against heat loss. The efficiency of thermal insulation is measured by its thermal conductivity (λ), expressed in W∙m⁻¹∙K⁻¹.

As for thermal conductivity (λ), it determines the steady-state heat flow passing through a unit area of a 1 m thick homogeneous material caused by a temperature difference of 1 K on its surfaces. This material is considered a thermal insulator when its conductivity is lower than 0.07 W∙m⁻¹∙K⁻¹ [32]. Studies on various concrete mixtures with the addition of hemp shive, conducted by Hryniewicz et al. [33], showed that samples containing 20–40% shive had the highest strength. The overall assessment of the samples indicates that hemp shive can be a good and ecological raw material substitute in precast concrete elements. The final strength of hempcrete also strongly depends on the length of the stalks, and it is recommended to keep them within 10–25 mm, based on the limited varieties of hemp available on the market. Typically, hempcrete is used for constructing internal partition walls and insulating external and internal walls in residential houses, holiday homes, and storage buildings. Its thermal conductivity (λ) ranges between 0.07 and 0.075 W∙m⁻¹‧K⁻¹ [30].

According to research carried out by Benfratello, using 40% of the fraction of hemp shives in the mixture resulted in a thermal conductivity coefficient of λ = 0.0899 W∙m⁻¹∙K⁻¹. By reducing the amount of hemp shives by half, this value increased to λ = 0.1406 W/mK [34]. Niyigena’s team conducted research with two types of shives, natural cement, and a small amount of citric acid. For 80 kg of the mixture, 8 kg of shives, 20 kg of natural cement, and 0.06 kg of citric acid were used [35].

Due to the biochemical composition of hemp shives (a component of hempcrete), they are not affected by microorganisms, and there are no fungi or molds. This is especially important in agricultural animal production processes, which can potentially be a source of large amounts of moisture and harmful gases. It is crucial to ensure proper microclimate conditions in such environments. Maintaining stable thermal conditions in piggeries is very important for animal welfare and ensures consistent weight growth.

Pigs require stable temperature conditions, particularly in areas where newborn piglets are kept, as they need a temperature range of 25–32 °C. Guidelines for ensuring the necessary conditions for the proper welfare of pigs are outlined in Council Directive 2008/120/EC of 18 December 2008, which sets minimum standards for the protection of pigs [36]. For this reason, modeling thermal conditions in piggery environments has become increasingly important [37]. In commodity farming, to ensure adequate growth rates of animals, the walls of buildings should have proper insulation and effective ventilation.

Embodied energy for buildings, including livestock buildings, refers to the total energy used to produce and transport a given building material to its destination [9,38,39]. A diagram illustrating the components of embodied energy for construction materials is shown in Figure 2.

The left side shows the components of the production process that are standardly included in energy expenditure analyses. On the right, very often omitted elements involved in the production process are listed, for which it is difficult to estimate energy expenditure due to the large diversity of methods and the subject itself—which can increase the error in the calculations.

The concept of embodied energy is crucial for further analysis and the selection of optimal solutions in the matter of insulation materials. Dixit [41] showed embodied energy factors in terms of joules per square meter for various insulation materials, while other authors use joules per ton. It is claimed that non-plant-based insulation materials, such as EPS, XPS, PU, PIR, phenolic foams, and PIB, have high values of embodied energy (EE) and embodied carbon (EC) [14].

Currently, there are no published studies on the suitability of biomaterials, including those using hemp, for thermal insulation in livestock buildings for animals whose minimum welfare requires the use of thermal insulation. What is novel in this article is the analysis of the potential use of biomass as a material for thermal insulation in livestock buildings, considering various raw materials, their physical and thermal properties, and the potential ecological benefits resulting from their implementation. The aim of the research is to assess the effectiveness of biomass as a thermal insulator, taking into account the perspective of sustainable development and improving energy efficiency in construction. This evaluation is based on indicators of embodied energy and carbon footprint.

2. Comparison of Thermal Properties of Different Materials, Including Biomass, as Insulation of Buildings

The concept of sustainable development and the requirement to implement the key principles of circular economy in the building and construction sectors are realized through the creation of sustainable thermal insulation materials. Plant fibers or recycled industrial and agricultural waste have strong potential for enhancing thermal comfort in buildings [41]. The main aim is to keep the thermal conductivity parameter (λ) at the lowest level, which results in savings on the thickness of the material used while maintaining a similar thermal effect [12,42].

A comprehensive review of the literature on the thermal conductivity coefficient (λ) of different materials is presented in

Table 1. Thermal conductivity coefficient λ of different materials: review.

Type of Material	Thermal Conductivity Coefficient [W·m−1·K−1]	Density [kg·m−3]	Source	No. of Reference
Rock wool	0.046	30–180	Zhao et al., 2023	[15]
		40–200	Palumbo et al., 2020	[43]
Mineral wool	0.03271–0.03688	77.7	Pomada et al., 2024	[19]
	0.031–0.035	30	Claude et al., 2023	[44]
	0.03126–0.03463	102.8–124.7	Wi et al., 2021	[45]
Expanded Polystyrene (EPS)	0.046	21.2–31.8	Koenen et al., 2024	[18]
	0.03126–0.03463	28.1–35.7	Wi et al., 2021	[45]
	0.041	18–50	Ali et al., 2024	[46]
	0.034–0.039	15–35	Bel, 2017	[47]
Extruded Polystyrene (XPS)	0.03422–0.03541	17.1	Pomada et al., 2024	[19]
	0.025–0.028	30.5–34.7	Wi et al., 2021	[45]
Low/medium/high-density panels hemp fibre or woody core	0.090–0.160 at 23 °C and 50% RH	200–600	Collet, Pretot, 2014	[24]
Hemp	>0.03	150	Koenen et al., 2024	[18]
Hemp shives composite	0.069.0–0.0759 (*)	210–410	Viel et al., 2019	[48]
	0.059–0.073		Kumar et al., 2020	[49]
Hemp shives	0.038–0.123	90–110	Hussain et al., 2019	[50]
Hemp–lime composites	0.051–0.058	360	Hussain et al., 2019	[50]
Pine wood	0.1237–0.1260	450–630	Kumar et al., 2020	[49]
		416–646	Trochonowicz, Szostak, 2023	[51]
Small corn stalk	0.045	109.6	Zhang et al., 2021	[52]
Large corn stalk	0.031	84.5
Wood fibre	0.065–0.37	230	Palumbo et al., 2018	[43]
Flax	0.038	20–100	Claude et al., 2023	[44]
Insulation foam made from wood waste (**)	0.038	60	Siciliano et al., 2023	[53]
Cork	0.036–0.065	65–240	Ali et al., 2024	[47]

(*) with wheat straw; (**) by RH 50%.

.

Generally, rock wool has poorer parameters, such as thermal conductivity and water absorption, compared to EPS, PU (Polyurethane), and XPS [15].

Wi et al. studied 21 different insulation materials, including organic materials like EPS, XPS, and phenolic foam, as well as inorganic materials like glass wool and mineral wool. The highest λ in their studies (0.037) was measured for samples made from mineral wool [43]. Both polystyrene and mineral wool have low thermal conductivities, making them efficient at minimizing heating needs [42].

Rock wool and glass wool are typical inorganic insulation materials with thermal conductivity lower than 0.046 W∙m⁻¹∙K⁻¹. Pedroso et al. [54] conducted research on the actual hygrothermal properties of insulating materials of biological origin used in buildings [53]. As a result of delignification, Siciliano et al. [53] obtained insulating foam made from wood waste with a low thermal conductivity (0.038 W∙m⁻¹∙K⁻¹) and high mechanical strength, making it a promising solution for effective building insulation.

Palumbo et al. (2018) [43] claimed that the thermal conductivity of corn-alginate insulations was similar to wood wool, but the denser wood-fiber board exhibited significantly higher thermal conductivity and lower diffusivity. EPS had a lower conductivity value, but higher (twice) diffusivity compared to CA (corn-alginate insulations) and wood materials. A comparison of hemp with mineral wool (rock wool) or conventional plastic insulating materials (polystyrene) at the same density was made by Florentin [55] and Korjenic [56].

Manufacturers of construction products provide information about thermal conductivity coefficients in their offers, which vary depending on the material type and its thickness. Mineral wool with a thickness of 200 mm and a density of 30 kg∙m⁻³ had a thermal conductivity of 0.035 W∙m⁻¹∙K⁻¹, the lowest among other materials such as flax, wood wool, panels made from gypsum, clay, or OSB boards (ranging from 0.100 to 0.353), according to Claude et al. (2023) [44].

Investigations by Collet and Pretot on hemp concrete’s thermal conductivity, based on experimental measurements and self-consistent scheme modeling, showed that thermal conductivity increases by about 54% when density increases by two-thirds, while it increases by less than 15–20% from a dry state to 90% RH (with low density at 250 kg∙m⁻³ and high density at 600 kg∙m⁻³) [24]. Viel also showed differences in thermal conductivity of hempcrete depending on density, ranging from 166.5 to 188 kg∙m⁻³, and humidity, from dry to 50% RH [49].

Experience with Canadian houses made from hempcrete provided valuable guidance for choosing the optimal density, which ranged from 220 to 627 kg∙m⁻³, while Collet suggested a density of 430 kg∙m⁻³. The best thermal conductivity values were found for densities between 250 and 360 kg∙m⁻³.

Other ingredients and additives, such as micro-cellular melamine foam supported by SiO₂ aerogel, are also a cost-effective and efficient way to improve the thermal conditions of buildings [57]. According to research by Haigh [58], polyurethane and fiberglass exhibited the lowest average thermal conductivity, whereas organic waste materials had the highest. Alrasheed [59] demonstrated a 78% reduction in heat loss from cylindrical transfer pipes equipped with a double layer of rock wool insulation. Ye et al. (2006) presented the thermal conductivity of wool as well as wool–hemp insulation [60].

According to research by Kuqo [61], insulating material based on wood fibers had a worse thermal conductivity coefficient and higher energy demand for processing compared to materials containing ecological grasses, such as seagrass leaves.

Depending on density, Tupciaukas obtained thermal conductivity values for different loose-fill thermal insulation materials ranging from 0.0401 to 0.0538 W∙m⁻¹ K⁻¹ [62]. Dhakal et al. (2017) investigated hempcrete and found thermal conductivity values between 0.074 and 0.103 W∙m⁻¹ K⁻¹ [63].

Based on the above research findings, the proper approach to improving the energy efficiency of the building and construction industry in an environmentally sustainable way is the use of insulating materials derived from biomass waste. The second important indicator, in addition to thermal conductivity, is embodied energy (EE), which allows for comparing and choosing the most effective solutions.

3. Comparison of Embodied Energy and Carbon Footprint for Different Construction Materials

The embodied energy depends, among other factors, on the distance between the building construction site and the locations where materials are produced or acquired using biomass.

Table 2. Thermal conductivity (W∙m⁻¹∙K⁻¹) and embodied energy [MJ∙kg⁻¹] for natural fiber insulation materials, according to different authors.

Insulation Material	Thermal Conductivity W∙m−1∙K−1	Embodied Energy MJ∙kg−1
Bagasse	0.049–0.055	2.96
Cellulose	0.037–0.042	3.3–10.5
Coffee chaff	0.076	0.23
Coir	0.04–0.045	0.55
Cork	0.037–0.050	26
Cotton stalks	0.058–0.082	44–48
Flax	0.033–0.090	39.5
Hemp	0.039–0.123	18.71
Juta	0.050	21.11
Kenaf	0.026–0.044	22.7–39.06

Source: [16] after: [50].

presents the overview of thermal conductivity and embodied energy [MJ∙kg⁻¹] for natural fiber insulation materials.

When comparing the embodied energy of basic building materials, it is much higher than that of insulation materials. For example, bricks and blocks have an EE between 0.9 and 4.6 MJ∙kg⁻¹ [38]. Basbagill et al. [64] report that the embodied energy of concrete is 1.13 MJ∙kg⁻¹. Jami et al. (2019) [65] claimed that hempcrete can achieve similar thermal properties (R-value) compared to cellular concrete with a density of 480 kg∙m⁻³.

The initial embodied energy in the production of Hemp–Lime (HL) material is considered lower than that of conventional building materials, as only about 1 MJ/kg of hemp shives is used in cultivating this plant. However, systematic analysis is still needed to more accurately quantify these energy savings [55].

The carbon footprint of insulating materials, such as mineral wool, hemp shives, and pine wood, varies due to differences in production and transportation processes, as well as their specific properties.

Carbon emissions per 1 kg of hemp shives range from 0.085 to 0.19 kg CO₂, depending on the particular study. Moreover, it appears that hemp–lime has a high CO₂ sequestration rate during both the hemp-growing phase—ranging from 1.5 to 2.1 kg CO₂—and the curing process of lime. During this curing process, lime solidifies back into limestone by reabsorbing CO₂ through carbonization over the building’s life cycle [55].

It is assumed that the net carbon storage of hempcrete ranges from 4.28 to 36.08 kg CO₂ eq/m², considering both carbon assimilation during growth and carbon absorption during the use phase [66]. Further, Pittau et al. reported a carbon uptake of −1.19 kg CO₂/kg (binder) by hempcrete [67].

These promising results suggest that hempcrete has the potential to be one of the best compromising building materials in the coming decades. Since hempcrete demonstrated strong insulating properties in the study, it was adopted as the material for the piggery walls, which will undergo further analysis and simulation as described in Section 4.

The literature review indicates the existence of a research gap among existing available sources on similar topics. Most authors are focused on selected aspects of construction and some material properties for utilization in this aspect, while the current challenge is the need for a comprehensive meeting of requirements of stringent environmental standards, energy efficiency and animal welfare. Therefore, this work combines aspects of carbon footprint calculation, accumulated energy (embodied energy), insulation parameters and the possibilities of use of easily available biomass.

4. Materials and Methods

In our study, model tests were conducted for a piggery building using the most popular thermal insulation material, rock wool, alongside an innovative biomaterial: hempcrete blocks made from hemp shives. The carbon footprint was compared by simulating two construction variants: traditional construction (TB) and hempcrete (HB), the latter made from a biomaterial, under conditions in Poland. The building is designed for livestock with typical dimensions intended for breeding pigs with a population of up to 27 LU (1 Livestock Unit equals 500 kg). It includes rooms for piglets, weaners, and fattening pigs, a sector for loose, gestating, and lactating sows, a technical room, and a vestibule. Traditional construction (TB) uses materials such as bricks, mineral wool, and aerated concrete (cellular concrete). The hempcrete building is made from cement, lime, and 30% hemp shives, following the recommendations of Hryniewicz et al. [33]. It is assumed that for both variants, TB and HB, the foundations will be constructed using the traditional system, i.e., made of concrete.

The walls of a piggery built using traditional technology (TB) consist of a structural layer that serves as the load-bearing structure, with an additional layer of thermal insulation (Figure 3).

Figure 4 and Figure 5 show a drawing of the livestock building that serves as the model for these considerations. These diagrams were used to calculate the amount of building materials used. Internal walls separating the technical room from animal production are made from aerated concrete blocks. The subject of our further analysis is only external walls.

As an alternative to traditional technology, buildings can be constructed using blocks containing hemp as the thermal insulation material. This solution was considered in our study as the second variant of hempcrete construction (HB).

Only the external walls have a load-bearing function and an insulating function against external conditions, which are the main determinants of the microclimate conditions inside the livestock building. The partition walls (internal walls) in both variants TB and HB are the same and were made from of AAC (autoclaved aerated concrete), and these data were not used for further calculations.

Foundations were not included in the subsequent calculations, as hempcrete is not designed to carry heavy loads from ceilings, roofs, or load-bearing walls [31,35]. It was also assumed that the roof structure would be identical for both variants, constructed using the traditional system, i.e., corrugated sheet metal with mineral wool insulation. This solution was applied in the calculations for both the TB and HB variants, but only external walls were used for further calculations.

The main technical data for the TB and HB variants are shown in

Table 3. Dimensions and main technical data for TB and HB.

Parameter	Value	Unit
Density of materials		kg∙m−3
brick	1800
glass wool	30
AAC	600
hempcrete	400
Thermal conductivity		W∙m−1∙K−1
brick	0.72
glass wool	0.045
AAC	0.38
hempcrete	0.123
Width of building (*)	15.00	m
Width of building (**)	15.45
Length of walls (*)	33.00
Length of walls (**)	33.80
Height of walls	2.25
Wall thickness	0.4
Surface of doors and gates	6
Windows surface in rooms, of which:
pregnant and loose sows	7.56
lactating sows	3.78
piglets	3.78
pigs	11.34	m2
forage room	1.89
toilet	0.81
Total windows area	29.16
Gates area	20.25
Total area of windows, doors and gates	49.41
Floor area	495

(*) internal, (**) external.

.

In the first stage, the volume and weight of the building materials used were calculated for both variants: TB and HB. The carbon footprint was then calculated for each version of the livestock building used in the simulation (TB and HB).

4.1. Specific Technical Data of the Proposed Building Model for Two Variants TB and HB

Simulation calculations were performed for an analogous spatial system for both the TB and HB variants.

The first building variant (TB) will be constructed using the traditional system, and the walls will consist of the following layers:

• Outer layer: Brick, 24 cm thick, with a density of 1800 kg/m³.
• Mineral wool (glass wool) insulation, 10 cm thick, with a density of 30 kg/m³.
• Inner layer: PGS foam gas silicate (aerated concrete, AAC, based on fly ash), 12 cm thick, with a thermal conductivity (λ) of 0.38 W·m⁻¹·K⁻¹ and a density of 600 kg/m³.

The second building variant (HB) is based on walls made of hempcrete.

According to Arnaud and Gourlay [69] the average density of hempcrete, measured from various proportions of mixed hemp shives, binders (of different types), and water, was 445 kg∙m⁻³. In our study, the density for hempcrete buildings was assumed to be 400 kg∙m⁻³. The typical thickness of hempcrete walls for a cold climate zone ranges from 0.35 to 0.4 m. For the purposes of modeling, the assumed thickness of the hempcrete walls in the tested HB model was equal to 0.4 m. This thickness, together with specific density, guarantees the expected thermal conductivity coefficient. In addition, it is commonly used for livestock buildings, guaranteeing adequate load-bearing strength.

4.2. Carbon Footprint Calculation Procedure and Economic Analysis

The carbon footprint of bio-based insulation materials can be calculated using the Life Cycle Assessment (LCA) methodology, which evaluates the environmental impacts associated with all stages of a material’s life. In our case, this assessment excludes the operational stage [70], making it more similar to the IPCC methodology [71].

For biomaterials used in thermal insulation, this generally involves the following formulas (Equations (1) and (2)):

$$\mathrm{C}\mathrm{F}=\sum \left({\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{i}}·\mathrm{M}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l} \mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\right)-{\mathrm{C}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n} \mathrm{s}\mathrm{e}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}^1$$

(1)

$${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{i}}={\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{P}\mathrm{R}}+{\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{T}\mathrm{R}\mathrm{A}\mathrm{N}\mathrm{S}}+{\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{A}\mathrm{P}\mathrm{P}}+{\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{E}\mathrm{N}\mathrm{D}}$$

(2)

¹ For biomaterials.

• where:
• CF—Carbon footprint (measured in kg CO₂ equivalent).
• ${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{i}}$—Global Warming Potential of each material (kg CO₂e/kg of material) and for particular stages of the life cycle.
• ${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{P}\mathrm{R}}$—Global Warming Potential for stage: Extraction and Production.
• ${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{T}\mathrm{R}\mathrm{A}\mathrm{N}\mathrm{S}}$—Global Warming Potential for stage: Transportation.
• ${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{A}\mathrm{P}\mathrm{P}}$—Global Warming Potential for stage: Application.
• ${\mathrm{G}\mathrm{W}\mathrm{P}}_{\mathrm{E}\mathrm{N}\mathrm{D}}$—Global Warming Potential for stage: End of Life.
• Material mass—The total mass of the material used.
• Carbon sequestration—The amount of CO₂ absorbed by the biomaterial during its growth in the ground and/or during the calcination of lime.

The following steps were considered for GWP and are described below:

Extraction and Production: Calculate the emissions from harvesting or sourcing raw biomass, including processing it into insulation materials.

Transportation: Add the emissions from transporting materials to the building site.

Application: Include any emissions associated with the installation of the insulation.

End of Life: Account for emissions from the disposal, recycling, or composting of the insulation material.

The GWP of different insulation materials varies, depending on the individual physical features of each material.

For example, according to Alsaqabi et al., the highest GWP for rock wool is 738 kg CO₂ eq at a density of 120 kg∙m⁻³ [72].

According to hemp brick producer ISOHEMP, the thermal conductivity of blocks with a thickness of 36 cm is 0.071 W/mK, the compressive strength is 0.2 MPa according to EN 772-1, and the bulk density is 320 +/− 10% [73].

In our study, we assumed GWP values for mineral (glass) wool (MW), brick (B), AAC concrete, and hempcrete blocks (H). This indicator, frequently used in LCA analyses, was assumed according to the IPCC [71] and the Circular Ecology database [74] to evaluate the impact of a product on global warming throughout its lifecycle. It considers all gas emissions, which are calculated in terms of kilograms of CO₂ equivalent.

Further, Equation (1) subtracts the carbon sequestration that occurs during the material’s growth (for example, trees absorb CO₂ as they grow). Bio-based materials often have a net-negative carbon footprint due to this sequestration effect. Carbon sequestration in building materials can either be measured (using SEM image analysis in the laboratory) or estimated based on available scientific knowledge [74]. In their 2020 study, Arehart et al. found the potential sequestration of hempcrete and stated that it can sequester up to −16 kg CO₂e/m² (with U = 0.27 W/m²K) over its lifecycle [75].

In our study, we set this parameter at −1.8 kg CO₂e per 1 kg for hempcrete, following Florentin et al. [55] who reports this value, also taking into account the findings of Cosentino [76].

For economic analysis, the average market prices of individual materials included in the individual TB and HB variants were used.

5. Results and Discussion

Calculations of the volume, mass, and carbon footprint of particular layers for the TB and HB variants are provided in

Table 4. Calculations of volume, material weight, and carbon footprint for TB and HB.

Elements of Building Walls	Volume of Element [m3]	Density of Material [kg·m3]	Weight of Element [kg]	GWP [kg CO2 eq per kg of Material]	Carbon Footprint [kg CO2e]
Layer of brick	38.1420	1800.00	68,655.60	0.24	16,477.200
Layer of insulation made of glass wool	15.8925	30.00	476.77	8.63	4114.396
Layer of aerated concrete	19.0728	600.00	11,443.68	0.17	1945.425
Total carbon footprint traditional construction (variant TB)	−	−	−	−	22,537.02
Hempcrete wall (variant HC)	63.57	400	25,428	0.08	2034.24 1
Carbon sequestration	−	−	−	−	−45,770.40
Total carbon footprint	−	−	−	−	−43,736.16

¹—without carbon sequestration.

.

The carbon footprint of hempcrete (HB variant, without considering carbon sequestration) is only 9.02% of that of the traditional building (TB).

The carbon sequestration (carbon content) of hempcrete is relatively high, due to high CO₂ absorption during the growing process of hemp and it could be a few times higher compared to other growing plants but it is more similar to that of trees. Because cellulose takes 70%, hemicellulose 22%, and lignin 6% of hemp stem dry weight, it could be calculated that 1 hectare of hemp stem contains from 7.47 to 11.25 t of CO₂ absorbed. While mineral wool is a good insulation material, with relatively low thermal conductivity, hempcrete offers more advantages. Research conducted by Claude et al. [45] showed that mineral wool panels combined with gypsum board had lower thermal conductivity (0.220 W∙m⁻¹ K⁻¹) than panels made of wood wool combined with clay (clay board) (0.353 W∙m⁻¹ K⁻¹).

These studies indicate the potential of replacing traditional building materials with plant-based biomaterials, which could lead to a reduction in greenhouse gas emissions. The U coefficient (heat loss coefficient) for internal walls equals U ≈ 0.33 W∙m⁻²∙K⁻¹ and is identical for both TB and HB variants [68]. The U coefficient for external walls for TB variant equals U = 0.33 W∙m⁻²∙K⁻¹ and for HB variant is 0.292 W∙m⁻²∙K⁻¹, which is a result of the thickness set for particular layers and their thermal conductivity coefficients (Table 3). It could be said that the heat loss in both variants is similar.

Such solutions can be applied to new buildings or in the case of necessary modernization of livestock building structures. Particular attention should be given to selecting an insulating material with an appropriate heat transfer coefficient, which is closely linked to the material’s density and, consequently, its total weight. This, in turn, affects the overall carbon footprint.

Assuming that 30% of the volume of the hempcrete mixture is shive, the total mass of shive in our HB variant model is 25,428 * 0.3 = 7628.4 kg, or 7.628 tons. If we assume that 1 ha of hemp crops yields from 8 to 12 tons of dry biomass [77], the shives yield will range from 4 to approximately 7 tons, which will be sufficient for the construction purposes of the HB variant.

Lime-based composites with hemp, used in the HB variant, have better properties than conventional concrete. They are lighter, offer good insulation properties (thermal conductivity), and do not require additional insulation [78]. A pioneering study by Todde et al. [79] showed relative energy savings of 36.8 GJ and an emission reduction of 641 kg CO₂ eq/ha from industrial hemp grown on contaminated soil under a low-input scenario, when tailored for bioenergy production. For comparison, according to the IPCC report, the embodied energy for concrete blocks ranges from 0.83 to 1.25 MJ/kg of material. The counterpart of embodied energy, which is used to estimate the total energy contained in buildings, is cumulative energy, a universal method for assessing energy consumption in agriculture and other processes [80,81,82].

In addition, we performed the cost analysis of TB and TH variants. The results are shown in

Table 5. Comparison of costs for TB and TH variants.

Variant	Material for Variants	Average Market Price [EUR·m−2]	Estimated Cost of External Walls [EUR]
	Layer of brick (0.24 thickness)	45	7151.62
TB	Layer of insulation made of glass wool	7.55	1199.88
	Layer of aerated concrete	13.2	2098.00
		Total for TB variant	10,449.50
TH	Hempcrete	65	10,330.125

.

A cheaper variant of the experiment presented in our article is the HB variant, i.e., walls of the pigsty building made of hempcrete, but it is not a significant difference. Due to the ease of construction and lower transport costs (i.e., carrying out the investment near the place where bio-waste (hemp shives) is created), this method of using hempcrete is profitable when used in livestock construction in rural areas.

The cost effectiveness of hempcrete is improved by recycling it and reusing it for new constructions. Taking into account that hempcrete is a strong environment-friendly solution, it should have some kind of governmental incentives, especially in countries which are at the beginning of the way of energetical transformation towards zero-emission industry.

6. Conclusions and Practical Recommendations

The HB method, due to its simple composition and reduced importance for transport and assembly, will greatly simplify and facilitate the construction of livestock buildings in light of the trend toward intensifying animal production. However, attention must be given to the issue of properly storing insulating materials.

Storage of particulate biomass, such as wood chips or other biomass materials, is associated with the risk of increased material temperature and subsequent decomposition. This issue can be mitigated by conducting simple laboratory tests to evaluate the moisture content of the stored material and the relative humidity of the surrounding air.

The main goal of this article was to assess the potential use of biomass from local countryside products in developing thermal insulation walls in agricultural animal buildings. To explore differences, two types of piggery construction were presented: one using typical concrete materials and the other using biomass-based materials for thermal insulation walls. The analysed structures TB and HB have the comparable heat loss, but they differ with carbon footprint.

For the traditional building variant, TB, the carbon footprint was equal to 22,537.02 kg CO₂ eq, while for the bio-based insulation variant of hempcrete building it was equal to −43,736.16 kg CO₂ eq.

The carbon footprint evaluation of bio-based materials often results in a net-negative effect due to the sequestration process, which can be further optimized through modifications in the processing stages. It could be achieved by cultivation of the newly developed genetically modified varieties of industrial hemp plants, with higher growth potential on poorer soils, i.e., for recultivated areas of countryside.

There is still possibility for the use of hempcrete for large livestock facilities which do not need multi-floor constructions. The perspective for development of such a building market is very good. The advantage of variant HB is it simplifying the building process. Besides that, hempcrete can be used wherever there are large fluctuations in air humidity. The challenge for the future of livestock buildings made from hempcrete will be adaptation of general bio-based materials to obtain globally recognized certifications like ISO or others. Often, designers do not reach for modern biomaterials for this reason. So far, no clear research has been carried out that would suggest the need to exclude hempcrete for the construction of livestock buildings due to the presence of ammonia and traces of hydrogen sulphide in the air inside the building.

The findings of the study are based on carbon footprint and embodied energy indicators. The model calculations developed in this article may be used in the future for LCA analyses of specific construction solutions for rural livestock buildings.