Keywords

1 Introduction

In an era defined by environmental concerns and resource scarcity, the construction industry faces the imperative to shift toward sustainable practices. At the forefront of this evolution are sustainable buildings, which strive to minimise their ecological footprint while maximising their functionality, comfort, and aesthetic appeal. Important in the realisation of sustainable buildings are innovative façade systems, particularly those that harness the strength and versatility of steel to create high-performance and environmentally conscious structures.

According to the 2022 Global Buildings Climate Tracker and the United Nations Environment Programme, the construction sector and buildings are off track to achieve decarbonisation by 2050 [1, 2]. The report shows a negative trend in the decarbonisation of the building sector, achieving higher emissions since 2020. Greenhouse gas (GHG) emissions within the construction sector could be mitigated by reducing the embodied carbon footprint of the building accountable for extraction of raw materials, manufacturing of building materials, transportation of building materials, energy consumption related to the construction process, energy consumption related to the demolition/deconstruction process, transport of construction waste, construction waste process, and disposal. The reduction in construction materials emissions can be achieved through the use of renewable and recycled materials, the reuse of construction materials and components, the use of alternative materials with lower emissions and the adoption of sustainable manufacturing processes [3,4,5]. Reducing GHG emissions in the construction sector by addressing waste from construction materials may be achieved through recycling materials and reusing components at the end of buildings’ lifespan, through design for deconstruction, upcycling materials for second lifespan, and using prefabricated construction elements [6,7,8,9].

A steel-intensive façade system is a building envelope that prominently features steel elements as a primary structural component and as an aesthetic component. Traditionally used in agricultural and industrial construction, in last decades steel-intensive façade systems have faced a growing demand in retail, commercial, and educational buildings [10]. Whether in the form of built-up wall steel insulated panel cladding systems, sandwich panel or liner-tray wall systems, or in the form of single skin façade panels and modular cassettes, steel-intensive façade systems have attracted increasing interest in the construction sector due to their strength, flexibility, and recyclability characteristics, emerging as a particularly inviting path to achieve sustainability goals.

In general, industrial buildings have a shorter lifespan (commonly 20–25 years, after which these buildings are usually replaced due to a change in demand) than other types of structures (50–100 years), leading to a higher ratio of embodied carbon to operational carbon compared to longer-lasting structures. This emphasises the importance of assessing the impact of materials and construction processes, as the proportion of embodied carbon emissions might be relatively higher. In the last decade, in the industrial hall and warehouse sector, approximately half of the structures were covered with sandwich panels and 50% with built-up systems with two skins [11].

The current results of research from studies that examine the life cycle of buildings have generated notable changes in the construction sector, guiding efforts to reduce emissions and improve energy efficiency [12, 13]. Thus, this study aims to contribute to existing research by a comprehensive analysis of the environmental impact of the most used industrial hall envelopes: sandwich panels and liner tray cladding systems as the latter have emerged as a promising technology that has the potential to transform the landscape of industrial construction.

2 Life Cycle Assessment of an Industrial Hall with Steel-Intensive Façade Systems

The purpose of the LCA presented in this paper is to assess the characteristics of single-storey steel-intensive systems using liner trays cladding systems and sandwich panels as envelope systems, through environmental impact analyses. The assessment includes single-storey steel structures made of completely new materials, as well as structures made of reused elements for the entire structure, for components (elements of the primary structure), or just for some individual members of the structure.

The case study is based on a LCA of a single-storey industrial building erected in Timisoara, Romania, and for the cases in which reclaimed steel elements were considered, it involved relocation from Germany to Romania.

Six scenarios for single-storey steel structures were selected for the environmental impact assessment (locations are important for transportation assessment):

  • Baseline scenario (Case 0) in which the structure is designed as a new structure made with elements from new materials;

  • The second scenario (Case 0+) considering a structure made of new elements with new materials, while the structure is designed for deconstruction;

  • The third scenario (Case 1) referring to a relocated steel structure, considering the reuse of an existing steel structure that originated in Germany and was reassembled in Romania (after it was adjusted to local seismic requirements);

  • In the fourth scenario (Case 2) it is weighted a steel structure made with reclaimed elements: existing profiles for beams and columns have been identified in a storage yard in Germany, which are deriving from other deconstructed buildings, and transported to Romania to be reused in a new industrial hall. All other components were made of new steel;

  • The fifth scenario (Case 3) is similar to Case 2, considering reclaimed elements such as columns and beams, but also end plates for beams and columns. All other components represent new steel;

  • The sixth scenario (Case 4) considers the reuse of an entire structure relocated from Germany. The percentage of steel reused in the superstructure is 100%.

The envelope considered for each case scenario involved two plots (Fig. 1): a) steel sandwich panels with mineral wool insulation (120 mm sandwich panels for the roof) and liner tray wall cladding with mineral wool insulation (100/600/0.75 liner trays with 60 mm mineral wool insulation for the walls) and b) solely sandwich panels with mineral wool insulation (120 mm sandwich panels for the roof and 80 mm sandwich panels for the walls).

For Cases 1 to 4, where the analysis involved reused materials, only the liner trays were considered for reuse - thermal insulation and outer steel sheet were considered in the investigation as new materials, as well as the sandwich panels used for the roof.

Fig. 1.
figure 1

Typical wall sandwich panel (a) and liner tray wall system (b) [14].

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At the same time, for Cases 1 to 4 when the envelope was considered solely of sandwich panels, the existing envelope containing 80 mm steel sandwich panels with mineral wool insulation was reused, but to comply with the U-values existing in Case 0 and 0+, an additional layer of 60mm sandwich panels (new elements) was added to the entire envelope. The cross-section of the envelope consisting of sandwich panels is presented in Fig. 2.

Fig. 2.
figure 2

Cross-section of envelope solution based on sandwich panels: a) envelope for Case 0 and Case 0+ b) envelope considered for cases 1 to 4 (image generated with [15]).

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2.1 System Boundaries

The environmental assessment considered the following system boundaries for the described case studies:

  • The main components of the building are the foundations and the ground floor slab (concrete and steel rebars), the steel load-bearing structure (hot-rolled and cold-formed steel elements), sandwich panels for the roof (steel sandwich panels with mineral wool insulation), liner trays cladding system or sandwich panels for the walls, triple glazed windows and sectional sliding gates;

  • Other materials and components considered in addition to steel:

    • concrete foundations and concrete floor: 185 m3;

    • triple-glazed windows: 22.5 m2;

    • sectional sliding gates: 48 m2;

  • The steel rebars were counted as new material, with an input of 73% steel scrap in the manufacturing process and an end-of-life scenario with 95% recycling potential and 5% landfilling or material loss after sorting [16];

  • The U-value considered in the assessment is in accordance with the Romanian standard in force [17]:

    • for the external walls - 0.56 W/m2·K;

    • for roof elements - 0.34 W/m2·K;

    • for ground floor slab - 0.76 W/m2·K;

    • for windows and sectional sliding gates - 1.3 W/m2·K;

  • The heated floor area of the industrial hall is 525 m2, for Cases 0, 0+, 2, 3, 4 having a total length of 30 m, with six identical frames in a bay of 5 m, a 17.5 m span and 6 m height at the eaves. In Case 1 the structure has 551.25 m2 as the structure had to withstand higher loads than in Germany, thus the structure to be rebuilt in Romania has a length of 31.5 m, 7 bays of 4.5 m, and a width of 17.5 m in contrast to the structures in the other cases where they;

  • The operational lifetime of the building is considered as 25 years.

2.2 Assessed Scenarios for the Environmental Impact

The LCA carried out presents a cradle-to-grave analysis, including loads and benefits beyond the system boundaries using the LCA software Sphera Solutions GmbH 2021 [18]. The declared functional unit in the analysis is one industrial hall including load-bearing structure, foundations, envelope, etc.

In the Production Stage (modules A1–A3) it was considered the manufacturing of the load bearing structure, foundations, floor slab, envelope, windows, and industrial sectional doors. LCA results are calculated for each case scenario considering a “new structure with new materials” and “reused elements” in which different amounts of reused steel were evaluated from the deconstructed industrial building halls. The product stage for reused elements includes blasting and coating (where required) [19].

In the Construction Stage (modules A4–A5) the assessment includes the transportation of all construction materials from the manufacturer to the building site (distances between 10 and 70 km), the transportation of equipment and the erection of the structure. For the reused steel structure (Case 1) and the reused elements (Cases 2, 3, and 4) the distance considered for the transport of the reused steel relocated from Germany was 1200 km. Building construction included the excavation of soil for the foundation and floor slab, the concreting and assembly of the steel structure and envelope using a 10t autocrane, forklifts, manlifts, wheel loader, bulldozer, excavator, concrete pump and packaging waste processing [18,19,20].

The life expectancy of the industrial hall in each case studied in this assessment is 25 years, with therefore maintenance (B2), repair (B3), replacement (B4) of elements, or refurbishment (B5) were not considered during the Use Stage (modules B2-B5). Evaluation of operational energy consumption was based on the energy demand for a distribution warehouse [21] and includes energy use for heating, cooling, lighting, IT, security, computers, and other systems. In the assessment, neither heat recovery nor mechanical cooling was considered. A similar heat transfer coefficient was targeted for all envelope systems (new or reused materials). The envelope systems have been compared using the dedicated online Ubakus software [15]. External and internal temperature values considered for the evaluation were −5 ℃ and 20 ℃, respectively.

In the End-of-life Stage (modules C1–C4) the end-of-life scenario for each of the six cases studied involved an instance of ‘‘demolition and recycling” and another one of ‘‘deconstruction and reuse” (Module C1). It was assumed that the energy demand for the demolition of the steel load-bearing structure is 0.239 MJ/kg of steel product if the product is recycled and 0.432 MJ/kg of steel product if the product is reused [22]. For cold-formed steel elements, the impacts of deconstruction were modelled based on data from the literature on energy use in demolition, accounting for 0.085 kWh of diesel-powered machinery work per kg of steel deconstructed [23]. For concrete, the environmental impact included the use of diesel in the demolition process [24], while for reinforcement it included the consumption of diesel for the recovery of the reinforcement from crushed concrete [16]. The steel structure deconstruction process follows the reverse assembly process, to which additional effort is added to preserve the integrity of the deconstructed components for reuse [25, 26]. Where no other data were available, the supplementary effort was generated in the study as a 1.5 workload multiplier for the number of elements reused in the end-of-life.

The calculation model used for the assessment of Module D – Climate Change total [kg CO2eq] is based on an innovative calculation model [27], compatible with the methodology of the EN 15804 standard [28]. The calculation is based on the input and output of recycled and reused materials, the impact of virgin material production, and the impact of theoretical pure recycling.

3 Results of LCA

The environmental impact of the assessment was expressed using Total Climate Change as a pointer following the rules described in EN 15804 [28], EN 15978 [29] and ISO 14044 [30].

The LCA comparison (modules A-C) between cases with liner tray wall cladding and cases with sandwich panels envelope is presented in Fig. 3. The results of this comparison show that the Climate Change Total is higher in cases where structures are built with new materials and have liner tray wall cladding envelopes, regardless of the end-of-life scenario. The difference in additional 15–16 t of CO2 e in these cases is mainly correlated with two stages of the life cycle: The highest amount of these additional emissions is recorded in the production stage (A1–A3) due to the high amount of steel and the environmental impact related to the steel production process present in the liner tray built-up wall system than in the sandwich panel envelope system; the rest of the amount of the additional emissions were recorded in the Construction Stage (A4–A5) due to the extra workload required by the installation of the liner tray built-up wall system, as double-shell systems in particular consist of many different individual parts.

Fig. 3.
figure 3

LCA comparison (A-C) between structures with liner tray wall cladding envelope and structures with sandwich panels envelope.

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However, Fig. 3 shows a clear trend of decreased rate of emissions in the reused case scenarios (Cases 1 to 4) for the structures with liner tray wall cladding envelope in both Demolition and Recycle scenario and Deconstruction and Reuse scenario. While close environmental impact results were recorded in modules A4–A5, C1–C4 for identical study cases with liner tray wall cladding envelope and sandwich panel envelope, a difference of 9.52–29.20 kg CO2 eq/m2 is registered in the Production Stage (A1–A3) when on an existing envelope consisting in sandwich panels is installed an additional layer of sandwich panels in order to comply with same heat transfer resistance of the façade as in the cases with liner tray cladding system.

The smallest environmental impact is shown by the case when the entire structure is built with reclaimed elements and the wall envelope is made of liner tray cladding (1171.67 t CO2 eq/m2) while at the end-of-life of the structure the materials are recycled.

In Fig. 4 is presented a comparison of impacts computed in Module D between structures with liner tray wall cladding envelope and structures with sandwich panels envelope. The benefits are reflected in the assessment as negative values. In all cases the highest potential benefits (negative values) appear for the structures which have a liner tray wall cladding envelope, and the highest loads (positive values) appear for the structures that have sandwich panels envelope system. Differences of 8–25% in the potential benefits and 11–19% in the potential loads are shown between the two envelope solutions.

According to the results, the highest potential benefits appear in Case 0 with a Demolition and Recycle scenario in the End-of-life stage for both envelope solutions. In this situation, the maximum potential benefit is recorded for structures that have a liner tray wall cladding envelope (–140.74 t CO2 eq/m2).

Fig. 4.
figure 4

Loads and benefits comparison (module D) between structures with liner tray wall cladding envelope and structures with sandwich panels envelope.

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4 Conclusions

Reusing building materials and components plays an important role in reducing the need for new resources and diminishing emissions related to the extraction of raw materials, transport, and production processes. Although reused construction materials might not immediately fulfil the entire demand of new building projects, integrating highly reusable materials, such as steel, from previous use phases can substantially aid in cutting down the embodied carbon footprint of the buildings.

The material selection, energy efficiency, and durability of the building envelope can also significantly impact the environmental impact of the building. It is essential to consider the design and materials of the building envelope carefully to ensure optimal energy efficiency and environmental sustainability.

The assessment presented in the paper is based on single-storey industrial halls and compares environmental indicators of a steel structure build with new materials, a steel structure designed for disassembly and four additional cases of steel structures focused on the reuse of an existing steel structure and/or reclaim of various elements based on the same building having envelopes consisting of liner tray cladding system or sandwich panels cladding system.

The findings of the LCA reveal that the Climate Change Total is elevated when constructions are built with new materials and have liner tray wall cladding envelopes. This holds true regardless of the end-of-life scenario, primarily due to the environmental consequences associated with the steel production process and the additional effort needed for installing the liner tray built-up wall system. When structures are built with reused elements or components and have liner tray wall cladding envelope, in both End-of-Life scenario (Demolition and Recycle scenario and respectively Deconstruction and Reuse scenario) emissions are lower than those of structures built with reused elements and having sandwich panels envelope systems.

When considering different envelope solutions, the LCA results reported here confirm that the highest potential benefits (8–25% higher) appear for structures which have a liner tray wall cladding envelope, and the highest loads (11–19% higher) appear for structures which have sandwich panels envelope system.

In addition to the potential benefits of LCA, a significant benefit in using liner tray cladding systems comes from the potential for possible reuse, which is clearly superior to the potential for repeated reuse of sandwich panels, contributing to further reducing the environmental impact of a cladding system even after its second life cycle.