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Article

Upscaling Natural Materials in Construction: Earthen, Fast-Growing, and Living Materials

by
Olga Beatrice Carcassi
1,*,
Roberta Salierno
2,3,
Pietro Augusto Falcinelli
2,
Ingrid Maria Paoletti
2 and
Lola Ben-Alon
1
1
Graduate School of Architecture, Planning and Preservation, Columbia University, New York, NY 10027, USA
2
Architecture, Built Environment and Construction Engineering—ABC Department, Politecnico di Milano, 20133 Milan, Italy
3
Management Engineering—DIG Department, Politecnico di Milano, 20133 Milan, Italy
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(18), 7926; https://doi.org/10.3390/su16187926
Submission received: 7 August 2024 / Revised: 6 September 2024 / Accepted: 9 September 2024 / Published: 11 September 2024
(This article belongs to the Special Issue Fast-Growing, Bio-Based Construction Materials as Key Drivers to a Net-Zero-Carbon Built Environment)
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Abstract

:
Despite the numerous advantages of using natural materials, such as fast-growing, living, and earthen materials, their widespread application in the construction industry remains limited. This research presents a perception survey, which investigates stakeholders’ perceptions regarding the market, regulatory barriers, and educational barriers, exploring experiences, motivations, and attitudes toward the adoption of natural materials in construction projects. The results capture variations in current practices and identify patterns for future directions, analyzed in a comparative manner to assess two geographical regions: Europe and North America. The results show that contractor availability, a lack of professional knowledge (mostly in Europe), and cost-to-value perceptions (mostly in the USA) are key barriers to adopting natural materials. The lack of awareness among construction professionals regarding technical aspects highlights the need for targeted training, while the lack of regulatory distinction between living and earth-based materials underscores the need for harmonized policies. By elucidating stakeholders’ perspectives and identifying key challenges, this research aims to inform policymaking, industry practices, and research initiatives aimed at promoting the use of a wider lexicon of construction materials. Ultimately, this study hopes to facilitate the development of strategies to overcome scalability challenges and accelerate the transition toward their implementation in mainstream projects.

1. Introduction

As one of the largest global industries, the construction sector plays a significant role in environmental degradation [1]. It accounts for a substantial portion of resource consumption, waste generation, and greenhouse gas emissions. For instance, the residential sector produces 27% of global energy consumption and 17% of CO2 emissions [2]. Construction products are responsible for 23% of human-related greenhouse gas (GHG) emissions [3], with more than half of those coming from cement and steel manufacturing, making it a substantial contributor to the climate crisis. Additionally, construction activities generate significant waste, often resulting in landfills and causing further environmental harm. Hence, there is an urgent need for sustainable alternatives.
Among existing sustainable practices, natural materials are defined as readily available, minimally processed, nontoxic, and engaging materials; they include substances that range from geological earth-based products to plant- and plant-like protists to living materials such as fungi [4]. These materials, derived from by-products and renewable sources, offer an environmentally friendly alternative to conventional construction materials, potentially reducing carbon emissions, enhancing energy efficiency, and minimizing waste [5]. Bio-based materials, including those derived from plant fibers, agricultural residues, and other natural sources, offer a sustainable solution to the environmental problems associated with conventional construction materials. These materials are often biodegradable, have lower embodied energy, and can sequester carbon dioxide during their growth phase, thereby reducing the overall carbon footprint of buildings [6]. Examples of bio-based materials, such as fast-growing and living materials, include bamboo, hempcrete, straw bale, and mycelium-based composites. Using earth-based materials, such as rammed earth and adobe, also presents significant environmental advantages, as they are locally sourced and require minimal processing [7].
However, despite their numerous benefits, the widespread application of earth- and bio-based materials in construction still needs to be improved, primarily due to various scalability challenges, and their application in the construction industry is often still primarily at the research stage. The transition from experimental scales to mainstream adoption faces numerous challenges, including technological limitations, market demand, and regulatory barriers [8]. These challenges hinder the scalability and cost-competitiveness of earth- and bio-based materials and restrict their integration into conventional construction practices [9,10]. Additionally, there is a lack of standardization and certifications, which affects both the quality assurance and market acceptance of these materials [11,12,13]. Moreover, approximately two-thirds of the barriers identified by the interviewees in the case of earthen construction in the study by Morel et al. [12] are non-technical and are largely overlooked in the scientific literature. This oversight could help explain why earthen architecture remains a niche market, despite its potential as an ideal construction material for addressing the current climate and economic crises.
The adoption and integration of earth- and bio-based materials in construction vary significantly across geographical regions due to the different conditions that govern the likelihood of these materials being implemented in construction projects.
This study assesses the current practices and perspectives among stakeholders based in Europe (EU) and in the US in a comparative manner. By investigating stakeholders’ perceptions and experiences, this study seeks to uncover the underlying factors influencing their adoption in construction. Understanding these regional differences is essential for identifying best practices and tailoring strategies to overcome scalability challenges alongside the technical ones. By addressing these challenges, this study hopes to inform policymaking, industry practices, and future research initiatives, ultimately facilitating the transition towards more sustainable construction practices [14]. Hence, this research aims to address the following research questions: (1) What is the likelihood of construction actors implementing earthen, living and fast-growing materials into the sector in Europe versus in the United States? (2) What are the main barriers that inhibit the diffusion of these materials? The overall goal of this work is to provide valuable insights into the industry’s current state, identify critical challenges, and suggest potential solutions to promote the use of sustainable materials in construction. This research includes four sections. In the following part, a background on these materials is provided to better understand their implications and current developments in construction. Additionally, the materials and methods are depicted in Section 3, while Section 4 addresses the findings of this study and provides a discussion of the results. Lastly, a conclusion is provided.

2. Background on the Adoption of Earth- and Bio-Based Materials

Earth- and bio-based materials encompass a wide range of natural elements, primarily categorized into geological materials like earth, sand, larger aggregates, and stone, and biological materials like vegetation, algae, agricultural waste, and plant fibers [4]. These materials can be used in construction by blending them into mix designs and methods, from adobe, cob, and light straw clay, to rammed earth and compressed earth blocks [15]. Bio-based materials can comprise a range of plant-based substances and living additives, from fast-growth fibers to bamboo and wood [16]. Although wood is considered a bio-based material, given its wide adoption, it is not included in this study in order to focus on emerging and re-emerging products.
Given the multiplicity of terms, as an encapsulating name, this paper will use “earth- and bio-based” moving forward. Additionally, in this study, materials are catalogized according to three main material families: (1) earthen, (2) living, and (3) fast-growing materials. For each material family, a schematic diagram of the final building material/product, their construction technique (monolithic, applied in free-hand, formwork), and their building application (e.g., structure, indoor/outdoor, modular) is proposed as a reinterpretation of the CRATerre wheel for earth construction [7].

2.1. Earthen Materials

Raw earth, a traditional construction material, has been used globally for millennia, displaying both universal and diverse characteristics in vernacular and monumental architecture across the world [17]. Evidence shows that people in almost every region of the world have resided and still are residing in earthen dwellings [18]. Earthen materials are locally available whenever clay-rich soils are present. Additionally, excavations in or around the construction site are ideal for construction, therefore minimizing extractive practices and transportation-related pollution [19]. Earthen materials are also nontoxic, non-polluting in nature, and able to absorb volatile compounds, enhancing their ecological appeal [20]. Raw earth’s thermophysical properties, such as its thermo-hygrometric regulation and high thermal mass, contribute to indoor comfort by stabilizing humidity levels and mitigating the impact of heat waves [21]. Comprising gravel, sand, silt, and clay, the material’s composition defines its application, with clay-rich soils often mixed with sand or natural fibers to prevent cracking and enhance strength. The variety of soil compositions has led to a diversity of earthen construction techniques, as shown in Figure 1.
More specifically, the primary use of these materials for structural, modular, and indoor/outdoor purposes, as highlighted in Figure 1, can be divided into three main categories: monolithic, applied in free-hand, and formwork. Earthen materials are mainly regaining momentum in the building sector for sustainability reasons, with the development of elements characterized by a high thermal mass performance and reduced production costs [22]. There are comparable advantages to both monolithic and formwork systems, such as a high compressive strength that guarantees good load-bearing properties [23]. With regard to the monolithic section, specific architectural components can be obtained via the implementation of various technologies, such as innovative 3D printing techniques [24,25,26].
The final products of various manufacturing techniques result in different construction possibilities. In the case of rammed earth components, they can be unstabilized or generally mixed with lime or cement and then compacted to achieve appropriate levels of density and strength [27]. Light straw clay is obtained by mixing wheat straw with clay slurry, then tamped as an infill within a structural frame [28]. Concerning formwork systems, they are mainly characterized by various block components, such as tamped, cut and pressed blocks [29]. These are generally mixed with a small percentage of stabilizers and finally compressed [30]. The use of soil as a construction material combines different production techniques, including mechanical and hand manufacturing. In the second one, which uses hand-shaped and hand-moulded adobe, soil is mixed with a certain amount of water and other organic materials, then shaped into brick form and dried off naturally [31]. The entire process is characterized by no use of specific machines, and that positively affects the overall reduction in energy consumption. Lastly, the adoption of plaster and cladding in interior spaces can increase their indoor quality, since chemicals and toxins are generally absent in soil plasters [22].

2.2. Fast-Growing Materials

Fast-growing materials (FGMs) such as bamboo, hemp, straw and flax have always been used in construction [32], e.g., the presence of FGMs in manufacturing since 7000 BC has been proven [33]. Due to their large availability, biodegradability and renewable nature, these materials are gaining momentum once again in construction as a valid and more sustainable alternative to petroleum-based materials [34].
Given their specific properties, FGMs can be used in several applications, as shown in Figure 2 where bamboo, hemp and straw are chosen as examples for this material family. For instance, bamboo, growing to maturity within three to five years, is known for its high strength-to-weight ratio and is mainly utilized in structural components [35]. More specifically, bamboo canes are mechanically cut and put together with reinforced connections in order to obtain structural elements, such as columns and beams, with a high compressive strength. Nevertheless, it can also serve other functions, such as in flooring and scaffolding.
Other materials, such as hemp and flax, can be harvested in just four months [36]. Hemp, particularly in the form of hempcrete, is fire-resistant and is increasingly utilized in construction to create blocks of different dimensions and applications, also participating in load-bearing structures [37]. On the other hand, in the form of fibers, due to their good performance in thermal and/or acoustic insulation, these materials can be used to constitute building partitions [38]. Hemp-lime, also known as hempcrete, is made with a combination of hemp shives (the woody parts of the hemp plant), a lime binder, and water [39]. Hempcrete is one of the most promising biodegradable high-strength natural materials [34].
Straw bales can also be used in walls and roofing, contributing to energy-efficient buildings [40,41]. Incorporating straw as a biobased construction material involves using the stalks left over from harvested grains like wheat or rice in building components [42]. For example, straw bales are utilized as insulating materials in walls, offering both thermal insulation and structural support [43]. This approach not only repurposes agricultural waste but also enhances the sustainability of the construction process.

2.3. Living Materials

Incorporating living materials like algae, mycelium, and bacteria in construction research and practices constitutes an important shift toward sustainable and eco-friendly building solutions, as shown in Figure 3. Algae, particularly microalgae, are utilized in bio-reactive facades, where they contribute to thermal insulation, carbon sequestration, and biofuel production [44]. These systems capture and utilize CO2, thus reducing greenhouse gas emissions. Mycelium, the vegetative part of fungi, has been vastly explored in small-scale experimental scales for its potential use in construction infill and self-healing attributes [45]. Mycelium-based composites, specifically mycelium-based foams, and mycelium-based sandwich panels have been recently explored for construction purposes [46,47,48]. Although moisture absorption hinders their widespread application, these materials show impressive mechanical properties and can be molded into various shapes, offering a renewable alternative to traditional materials [49]). Furthermore, recent studies have shown the promising thermal and acoustic performances of mycelium products [50]. Therefore, these materials find applications as infill panels or in interiors.
Bacteria are employed in bio-concrete, where specific strains precipitate calcium carbonate, sealing cracks and enhancing durability [51,52]. This biocalcification process not only extends the lifespan of structures but also reduces maintenance costs.

2.4. Natural Materials Taxonomy: EU versus US

The differences and gaps in governmental definitions, particularly regarding biogenic/bio-based materials, are underscored in Table 1. Definitions of the terms were sourced from the official primary websites of European (EU) and United States (US) institutions, specifically the European Commission (EC), European Environment Agency (EEA), US Department of Energy (DOE), and US Environmental Protection Agency (EPA). The EU definitions emphasize the origin of materials, while US definitions allow for both natural and synthetic processes. Additionally, the EU provides specific definitions for ‘biomass’ and ‘geogenic’, which are absent in the US context. None of these geographical regions offer an official definition for ‘earthen’ or ‘living’ materials. When assessing the renewability of materials, a consistent source was employed. In defining ‘bioregional’, the European approach uniquely incorporates geopolitical elements to describe regional interconnectedness.

3. Materials and Methods

3.1. Survey Questionnaire for Stakeholders

This research aims to investigate the challenges associated with the adoption of biobased and earth-based materials in construction, focusing on stakeholders’ perspectives. These findings, in addition to technical advancements in the scientific realm, are fundamental to their adoption by practitioners. The subject population includes actors involved in various stages of the construction supply chain and includes (i) production workers, (ii) designers and builders, and (iii) education experts.
The recruitment process utilized both purposive sampling (targeting specific individuals) and snowball sampling (recruiting additional experts through initial respondents). Initially, the purposive method involved sending emails to a selected poll of stakeholders. Subsequently, the snowball technique was used to identify more participants with similar experiences. Additionally, a self-selection sample was gathered through networking groups in conferences, networking meetups, and social media groups to increase responses and encourage more experts to take part in the study. This approach aimed to enhance the diversity of the participant pool; however, snowball sampling may introduce biases based on the networks of initial respondents. Despite this, the resulting sample demonstrated a considerable range of industry roles, geographic locations, and attitudes toward the adoption of local materials, which supports the study’s exploratory objectives.
To tackle the research questions, a four-part survey was distributed to stakeholders to collect quantitative data regarding their perceptions and experiences concerning the expansion of earthen, fast-growing, and living materials. Specifically, two geographical regions, Europe (EU) and the United States (US), were compared to capture variations across the two geographical regions.
The survey inquired about stakeholders’ perceptions of (i) market barriers, (ii) policy /regulatory barriers, (iii) the adequacy of training and education, and (iv) AI-generated imaginary futures as potential paths forward; these are detailed in the following sub-chapter. The first three parts were then delineated into 4 to 5 questions to answer, choosing from a 5-point Likert scale, where 1 represented “No barrier at all” and 5 represented “Extreme barrier”. In particular, stakeholders’ shared experiences, motivations, and attitudes toward the adoption of bio-based and earth-based materials were also evaluated.

3.2. AI-Generated Image Prompts

For the definition of the question “imaginary futures”, AI software was implemented to generate the set of images. The software used was “Midjouney”, model version 6.1, [71], a text-to-image AI service provided by the server “Discord” [72]. The question mentioned above was structured to give a multiple-choice response. Specifically, the response provides a set of paired options that enable the respondents to have a clear idea of the possible outcome of the choices. Figure 4 summarizes the set of chosen images. The paired options were associated with keywords. In particular, the set of keywords was constructed in five lines, each with two options:
Sustainability 16 07926 g004
Figure 4. AI-generated image of natural buildings for survey analysis. Digital image. Accessed via MidJourney platform, https://www.midjourney.com and https://discord.com, accessed on 5 August 2024.
Figure 4. AI-generated image of natural buildings for survey analysis. Digital image. Accessed via MidJourney platform, https://www.midjourney.com and https://discord.com, accessed on 5 August 2024.
Sustainability 16 07926 g004
To better describe the keywords and to instruct the AI, the software was provided with simple prompts containing the defined keywords and the specification of the materials, e.g., “/imagine a tall building made with bio-based or earth or living materials”. In the cases of lines 1 and 2 and line 4 (exterior), the context was specified, adding to the prompt “in an urban context”. In the case of line 4 (interior), the word “building” was substituted with the term “space”. Furthermore, concerning line 5, for the word “furniture”, the focus was shifted to the generation of furniture for interior spaces, while for the keyword “assembly”, the prompt was changed to the following: “/imagine: a wall section in which all the layers are assembled and made out of bio-based and/or earth and/or living materials”.
For each prompt, the software generated a set of four different images. Consequently, the challenge was related to the choice that seemed to best depict the imaginary futures of living and bio-based materials. All the variations would present objects with smooth textures or rocky/concrete aspects, often repeating similar outcomes. This condition results in an unexpected constraint, highlighting the limitation of the AI instrument. To overcome this barrier, it was decided that the process would be stopped when the most natural-looking scenario possible was achieved for each keyword.

4. Results and Discussion

A total of 50 stakeholders participated in the survey: 27 from Europe and 23 from the US. The stakeholders were divided according to three main phases of the building process: Production, Design & Build, and Education. Figure 5 shows that 11 stakeholders belonged to the production phase, 18 to the design and build phase and 21 to the education phase. Figure 5a also highlights the geographical origin of the stakeholders, with similar numbers for the Production phase, many respondents in the Design & Build phase being from the US, and the majority of those in the Education phase being from Europe. Figure 5b displays that the majority of the respondents were mostly familiar with fast-growing bio-based materials (58%), followed by 36% familiar with earth materials, and only 6% familiar with living materials. This trend of responses is in line with the technology readiness level of living materials, which represents an emerging field in the construction sector and still needs to be fully implemented, compared to bio-based and earth-based materials that have been used since ancient times. These results are also comparable to the information that is missing on the taxonomy of earth and living materials from a government perspective for both geographical areas.

4.1. Survey Questions

The structure of the survey included three sections, each of them focusing on a specific barrier. The first section considered market barriers and was articulated via five questions: (i) availability of materials and products, (ii) availability of contractors, (iii) material is not well-known by professionals, (iv) cost-to-value discrepancies, and (v) consumer’s negative perception of the material. In Figure 6a, it is possible to see a concentration of responses in the “significant barrier,” with 34% (n = 26) and 52% (n = 27) of respondents noting the availability of contractors and professionals’ lack of material knowledge.
The “Policy/regulatory barriers” section was articulated in four questions: (i) lack of building codes/standards in your location for the chosen material, (ii) lack of experience/ knowledge of building officials (EU: with local authorities) throughout the compliance process, (iii) lack of incentives (such as tax, bonuses, etc.) to use these materials, and (iv) hardship in obtaining insurance for the structure. Overall, the lack of experience/ knowledge of building officials was highlighted by many of the respondents as the most significant barrier with the highest pick of responses, for a total of 28 (i.e., 56%), as is shown in Figure 6b.
The last section, “Training/Education barriers”, consisted of four questions: (i) a lack of building or vocational training programs (professional building techniques) for building professionals, (ii) a lack of academic education (undergraduate and graduate level) in university, (iii) a lack of continued education (such as educational credits) for design and engineering professionals, and (iv) a lack of demo projects to educate homeowners. In this case, the most significant barrier was mostly on the professional side rather that at the university level. The lack of academic education only collected a maximum of 16 (i.e., 32%) responses as a “moderate barrier”, whereas the other three categories were mostly perceived as a “significant barrier” (Figure 6c).
The survey analysis shown in Figure 7, Figure 8 and Figure 9 is visualized using percentages on a Likert scale.
For the Market barriers (Figure 7), the Education respondents agreed that the availability of materials and products corresponds to a significant barrier, together with the availability of contractors (especially in the European region) and the cost-to-value discrepancies. On the other hand, the Production phase answers are more concentrated on the material knowledge of professionals, particularly in Europe, and consumers’ negative perceptions. In the Design & Build phase, stakeholders also stressed the scarce material knowledge of professionals, together with the cost-to-value discrepancies. In the USA, the availability of contractors and the material knowledge of professionals are seen as extreme barriers, while the majority of EU responses were associated with significant barriers. At the same time, the cost-to-value discrepancy led to 67% (n = 4) of the US Education answers correlating with a significant barrier, while only 33% (n = 5) of those in the EU did.
According to the experts, despite the growing interest in sustainable building materials, numerous barriers inhibit their widespread adoption. Durability, fire resistance, and susceptibility to weather conditions make it difficult to deploy and spread them in the construction market. Additionally, it has been highlighted that the differences in European and US methods and codes can hinder product exchange between these two locations. Bio-based materials often need to be imported into North America due to a lack of local production, and there are no harmonized standards to certify them accordingly. However, while material availability can pose a barrier from an educational perspective, Production stakeholders suggest that it is mostly the time and energy required to specify and implement new materials that can reduce profitability and, therefore, its use in the market. These materials are often not incorporated into building codes or standards, making them difficult to integrate into larger-scale projects. Some insurers and banks are hesitant to insure or finance projects using these materials, and the market does not yet value their performance or health benefits. According to some experts, this is due to a cultural resignation to the health risks associated with conventional building materials and a general acceptance of the status quo. Moreover, the regulatory testing and knowledge of these materials are limited, and contractors prefer affordable, reliable, and familiar materials. The lack of adequate infrastructure and machinery, as well as insufficient job opportunities in the field, further complicate their adoption. Building codes often lack specific regulations for these materials, and certifications or labels can pose obstacles. Contractors’ unfamiliarity with these materials and their association with being against modernization are also identified as significant market barriers. Finally, scaling up the use of new materials and developing fixed specifications are major challenges in this field.
With regard to “Policy/regulatory barriers”, Production phase experts in both the USA and Europe mostly agree on the problems associated with a lack of incentive (Figure 8). In both continents, both the Design & Build and the Education respondents tend to agree that there is a lack of experience and knowledge among building officials during the compliance process, highlighting how the government can hinder progress if it is not open to non-conventional solutions. Moreover, Education is also defined as a significant barrier to obtaining insurance for structural parts built with natural materials. For these barriers, the results are comparable for both Europe and the US and stakeholder types.
According to some respondents, despite some regional and localized initiatives, such as Department of Energy funding for ongoing hempcrete projects [73], there is no overarching policy framework or momentum for circular and regenerative economies in the United States. A perception of barriers exists, whether they are actual or not, exacerbated by a lack of understanding of the importance of deep sustainability, leading to apathy and resignation. For the case of hemp and lime bio composites, it has been emphasized that industry familiarity is a significant issue, with missing US testing and no harmonized EU standards. Furthermore, current construction standards and product certifications are not adapted to these materials and can be costly. The results also highlight a shortage of architects familiar with innovative building materials, such as compressed earth blocks, and a general lack of innovative building products.
In the “Training/Education barriers”, according to the Design & Build respondents, the lack of academic education only represents a moderate barrier (Figure 9). However, this question is mainly perceived as a significant barrier by the Education group, together with the lack of continued education, demonstration projects to educate homeowners, and training programs for building professionals. The latter is also identified as a significant barrier from the Production point of view, particularly in Europe.
In addition to the barriers mentioned, there is a significant lack of digital and online resources for self-education and training designers and engineers. Despite the availability of continued education for design and engineering professionals, there is still a shortage of scholarships and subsidies for these types of training. Moreover, traditional Academia’s focus on environmentally damaging materials like steel and concrete in its curricula increases the problem. Encouragingly, more universities are now focusing on the use of reusable, bio-based, and geo-based materials after a prolonged period of neglecting material research and application in architecture. To counter these barriers, some North American stakeholders have organized their own workshops to educate contractors on the use of their materials. Additionally, there are increasing numbers of demonstration projects to showcase these materials to homeowners, for both innovative and experimental solutions [74,75] and feasible realizations.

4.2. AI-Generated Imaginary Futures

The creation of natural material images through AI revealed the tool’s limitations, particularly in its database of existing natural solutions, suggesting that the algorithm needs to be further trained.
The AI-generated imaginary futures suggest some preliminary path forward in terms of possible cultural acceptance (Figure 10). To begin with, the low-rise building is identified as the most adequate building typology, with this being preferred by 84% (n = 38) of respondents, whilst the tall ones were preferred by only 16% (n = 7) of respondents. The use of natural colors (79%, n = 37) and textures (61%, n = 28) instead of white and smooth surfaces is also preferred by most of the experts. Furthermore, the most adequate use is seen for interior applications (65%, n = 32) instead of exterior ones (35%, n = 17) and in forms of construction assembly (77%, n = 33). These results suggest the intrinsic wariness of experts when imagining the future capabilities of natural materials in the construction sector.

5. Conclusions

This research utilized a questionnaire to identify the current market, policy/regulatory, and educational barriers to the adoption of fast-growing, living, and earth-based materials in contemporary construction. Fifty experts from Europe and the USA, spanning the Production, Design & Build, and Education sectors, provided valuable insights that were reported through a Likert scale survey.
The findings have significant implications for driving innovation and advancing sustainable building practices, with the potential to reduce the environmental impact and enhance the resilience of the construction industry. Notably, the majority of respondents highlighted the availability of contractors as a significant barrier to the widespread adoption of natural materials in both regions. In Europe, the emphasis was on the lack of professional knowledge about these materials, while in the USA, stakeholders identified the cost-to-value perception as a major obstacle.
The education sector revealed a low awareness of bio-based materials among current construction professionals and in both geographical contexts, underscoring the need for targeted training courses at the professional level despite the increasing adoption of these materials in academic settings. However, the taxonomy analysis suggested a lack of distinction between living and earth-based materials in national regulations, indicating the need for harmonized knowledge from a policy/regulatory perspective.
The results from the exploration of imaginary futures highlight the initial, concrete steps that stakeholders can immediately take to advance the transition from conventional to natural materials, with the next 20 years being critical to averting a climate disaster. A practical starting point is the application of these materials in low-rise building typologies, which offer a manageable scale for implementation. Even if full-scale adoption proves challenging, integrating natural materials into specific building components, such as technically robust assemblies, can serve as an effective early approach toward regenerative solutions.
Additional concerns include technical challenges that require coordinated efforts from research and innovation institutions to address the fire resistance, durability, and water resistance of these new materials.
Compared to similar studies found in the literature [10,12], this research focused on stakeholders’ perceptions according to their roles in the supply chain, specifically in the areas of Production, Design & Build, and Education, and by comparing different geographical locations. These contributions offer critical information that can shape policies, practices, and research efforts aimed at promoting the use of these sustainable materials in construction.
Although the experts’ sample reflects the still restricted number of stakeholders in the construction sector that are currently focusing on natural materials compared to conventional ones, the small number of participants represents a limitation of this analysis. In future studies, the number of participants and the geographical locations should be expanded to grasp the next significant challenges with respect to other regions. Additionally, AI tools require further training to improve the creation of natural material images.
On a broader scale, this research has the potential to benefit society by facilitating a transition to more sustainable construction practices. By identifying barriers and proposing actionable solutions, this study contributes to the development of strategies that can mitigate environmental degradation, improve public health, and stimulate economic growth within the construction sector.

Author Contributions

O.B.C.: Writing—original draft, Writing—review; Investigation, Editing, Software, Validation, Visualization, Data curation, Methodology. R.S.: Writing—original draft, Writing—review; Investigation, Software, Editing, Validation, Visualization, Data curation, Methodology. P.A.F.: Writing—review; editing, Investigation, Software, Visualization, Data curation, Methodology. I.M.P.: Conceptualization of this study, Investigation, Validation, Supervision, Writing—review and editing. L.B.-A.: Conceptualization of this study, Investigation, Validation, Data curation, Formal analysis, Writing—original draft, Supervision, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Science Foundation, grant number 2134488.

Institutional Review Board Statement

The study was approved by the Institutional Review Board of Columbia University (protocol code IRB-AAAV1329 and 05/29/2024).

Informed Consent Statement

Not applicable.

Data Availability Statement

Dataset available on request from the authors.

Acknowledgments

The authors would like to thank the assistants at the Natural Materials Lab for continuously contributing to its maintenance. The authors also acknowledge the valuable contribution and participation of respondents from the Northeast Biobased Material Collective (US-based).

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Current utilization of earthen materials in the construction sector.
Figure 1. Current utilization of earthen materials in the construction sector.
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Figure 2. Current utilization of fast-growing materials in the construction sector.
Figure 2. Current utilization of fast-growing materials in the construction sector.
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Figure 3. Current utilization of living materials in the construction sector.
Figure 3. Current utilization of living materials in the construction sector.
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Figure 5. Distribution of survey respondents (a) per stakeholder type and location (Europe vs. the United States), and (b) per material familiarity.
Figure 5. Distribution of survey respondents (a) per stakeholder type and location (Europe vs. the United States), and (b) per material familiarity.
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Figure 6. Survey responses analysis per (a) market barriers, (b) policy/regulatory barriers and (c) training/education barriers.
Figure 6. Survey responses analysis per (a) market barriers, (b) policy/regulatory barriers and (c) training/education barriers.
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Figure 7. Survey response analysis for material barriers per normalized scores.
Figure 7. Survey response analysis for material barriers per normalized scores.
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Figure 8. Survey response analysis for policy-regulatory barriers per normalized scores.
Figure 8. Survey response analysis for policy-regulatory barriers per normalized scores.
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Figure 9. Survey response analysis for training/education barriers per normalized scores.
Figure 9. Survey response analysis for training/education barriers per normalized scores.
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Figure 10. Survey response analysis of the imaginary futures of these materials.
Figure 10. Survey response analysis of the imaginary futures of these materials.
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Table 1. Terminology and definitions according to official European and United States government institutions.
Table 1. Terminology and definitions according to official European and United States government institutions.
Word and SimilarEurope (EU)United States (US)
Biogenic
Bio-based		Bio-based products are wholly or partly derived from materials of biological origin, excluding materials embedded in geological formations and/or fossilized [53]Bio-based materials refer to products that mainly consist of a substance (or substances) derived from living matter (biomass) and either occur naturally or are synthesized, or it may refer to products made by processes that use biomass [54].
BiomassThe mass of living or organic material, usually expressed as dry weight per unit area [55] Not Available
GeogenicGeogenic factors are those which originate in the soil, as opposed to those of anthropic origin (anthropogenic) [56] Not Available
Fossil fuelsCoal, natural gas and petroleum products (such as oil) formed from the decayed bodies of animals and plants that died millions of years ago [57].Fossil energy sources, including oil, coal and natural gas, are non-renewable resources that formed when prehistoric plants and animals died and were gradually buried by layers of rock. Over millions of years, different types of fossil fuels formed -- depending on what combination of organic matter was present, how long it was buried and what temperature and pressure conditions existed as time passed [58].
Renewable(Focusing on energy not resources):
Energy sources that do not rely on fuels of which there are only finite stocks. The most widely used renewable source is hydroelectric power; other renewable sources are biomass energy, solar energy, tidal energy, wave energy, and wind energy; biomass energy does not avoid the danger of the greenhouse effect [59] 		(Focusing on energy not resource):
Renewable energy is energy produced from sources like the sun and wind that are naturally replenished and do not run out. Renewable energy can be used for electricity generation, space and water heating and cooling, and transportation [60]
Earthen materialNot AvailableNot Available
Living materialNot AvailableNot Available
Waste materialAny substance, material or object which the holder discards or intends or is required to discard [61] Differentiate all types of waste [62]
By- product materials
Co-products		The Waste Framework Directive defines by-products as a substance or object, resulting from a production process, the primary aim of which is not the production of that item. By-products can come from a wide range of business sectors, and can have very different environmental impacts. It is important to classify by-products correctly to avoid environmental damage or unnecessary costs for business [63]An incidental product deriving from a manufacturing process or chemical reaction, and not the primary product or service being produced. A by-product can be useful and marketable, or it can have negative ecological consequences [64]
Renewable raw materialsResources that have a natural rate of availability and yield a continual flow of services which may be consumed in any time period without endangering future consumption possibilities as long as current use does not exceed net renewal during the period under consideration [65]Resources that have a natural rate of availability and yield a continual flow of services which may be consumed in any time period without endangering future consumption possibilities as long as current use does not exceed net renewal during the period under consideration [66]
Bioregion
Bioregionality		A territory defined by a combination of biological, social, and geographic criteria, rather than geopolitical considerations; generally, a system of related, interconnected ecosystems [67] Any geographical region characterized by a distinctive flora and fauna [68].
NontoxicSubstances which are not toxic, as opposed to toxic substances: a chemical or mixture that may present a risk or injury to health or the environment [69].As opposed to toxic substance: A chemical or mixture that can cause illness, death, disease, or birth defects. The quantities and exposures necessary to cause these effects can vary widely. Many toxic substances are pollutants and contaminants in the environment [70].
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Carcassi, O.B.; Salierno, R.; Falcinelli, P.A.; Paoletti, I.M.; Ben-Alon, L. Upscaling Natural Materials in Construction: Earthen, Fast-Growing, and Living Materials. Sustainability 2024, 16, 7926. https://doi.org/10.3390/su16187926

AMA Style

Carcassi OB, Salierno R, Falcinelli PA, Paoletti IM, Ben-Alon L. Upscaling Natural Materials in Construction: Earthen, Fast-Growing, and Living Materials. Sustainability. 2024; 16(18):7926. https://doi.org/10.3390/su16187926

Chicago/Turabian Style

Carcassi, Olga Beatrice, Roberta Salierno, Pietro Augusto Falcinelli, Ingrid Maria Paoletti, and Lola Ben-Alon. 2024. "Upscaling Natural Materials in Construction: Earthen, Fast-Growing, and Living Materials" Sustainability 16, no. 18: 7926. https://doi.org/10.3390/su16187926

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