Life cycle environmental benefits of a forward-thinking design phase for buildings: the case study of a temporary pavilion built for an international exhibition

Abstract

The life cycle of a pavilion built for an international exhibition was investigated to understand the role that the design phase may play in the environmental sustainability of buildings. The limited life span of the structure allowed for a complete life cycle assessment (LCA) based on primary data to be undertaken, including the end of the first life. A methodology that considered an extension of the service life was applied to estimate the environmental impacts of distinct end-of-life scenarios. Results confirmed the paramount importance of the design phase in improving the life cycle sustainability of buildings. Accurate selection of materials allowed to markedly reduce the impact of the product stage (e.g. 37% fewer greenhouse gas emissions). Design for disassembly proved to be a necessary but not a sufficient condition to minimise the end-of-life impacts: design phase should not be limited to the appropriate selection of materials and components’ connections but must also foresee a second use for the structure or the materials at the end of the first life. Forecasting an after-life for the structure could reduce the life cycle burden up to 40% for several environmental impact categories. Conversely, if the second use is not predefined, the economic cost in the dismantling operation could become the priority rather than the salvaging of the components. Results of the present study may be used by future (temporary) building designers to improve the sustainability of their structure and to avoid the errors identified in the present case.

Introduction

According to the 5^th assessment report of the IPCC, buildings consume 32% of the primary energy produced worldwide and 51% of the global electricity (Lucon et al., 2014). Considering that 82% of the primary energy is still produced by fossil fuels (International Energy Agency, 2016a), the role that buildings could play in tackling climate change is significant. Moreover, figures presented in the IPCC report are limited to the operational phase of buildings, while in a life cycle perspective environmental impacts extend beyond the energy used for lighting, heating and cooling (Cabeza et al., 2014). For instance, almost half of the raw materials extracted globally are fabricated into building components (WU, 2016). In addition, demolished structures are responsible for massive waste generation: in Europe, construction and demolition (C&D) waste accounts for 33% of total waste streams, corresponding to approximately 1.65 t per inhabitant per year (Eurostat, 2012; Zabalza Bribián et al., 2011). The environmental burden of the pre-use stage (i.e. raw materials extraction, manufacturing processes, transport of the components to the construction site and building construction) and the end-of-life (EOL) is even more substantial, in regards to a building life cycle, when newly-built constructions are considered (Citherlet and Defaux, 2007). As a matter of fact, compared to traditional buildings, new buildings are characterised by lower energy requirements for the operational phase but also by a greater amount of energy that is embodied in the supplementary materials necessary to improve the energy efficiency of the structure (Huberman and Pearlmutter, 2008). The shifting of the environmental burden from the operational phase to the pre-use and after-use stages represents a real risk (Blengini and Di Carlo, 2010). Considering the variable role of the life cycle stages, the most appropriate tool to evaluate the environmental performance of a building is the life cycle assessment (LCA) (Pacheco-Torgal and Jalali, 2011). With a life cycle approach, the role that the minor stages and a careful selection of materials play on the overall sustainability is brought to light. Results of LCA analyses reveal that the contribution of these phases can exceed the 50% of the global impact in low-energy houses (González and García Navarro, 2006). Nevertheless, modelling choices of construction materials (e.g. data source, boundary definition, replacement scenarios) still have a clear influence on building LCA results (Häfliger et al., 2017).

The use of materials with good life cycle environmental performances, certified by Environmental Product Declarations (EPD) according to the ISO 14025 guidelines (ISO, 2006a), is now encouraged and recognized by building rating systems focused on environmental sustainability, such as LEED (Franzoni, 2011; U.S. Green Building Council). On the other hand, the development of construction techniques aimed at recovering the materials after demolition is not yet a priority (Thormark, 2006). Although the environmental benefits of recovering the materials are evident (Ghose et al., 2017) and the rating systems previously cited take into account the construction waste management, most of the buildings are still designed for a traditional demolition at their EOL. The long lifespan of buildings, typically longer than 50 years, and the uncertainties in the future value of the demolished materials inhibit the motivation to plan for a recovery of the building components (Guggemos and Horvath, 2005). While for existing buildings at their EOL the environmental impacts could be substantially reduced by selective deconstructing and repurposing instead of demolishing and reconstructing (Assefa and Ambler, 2017; Vandenbroucke et al., 2015), a strategy to reduce the future cost of demolition and the single-use approach of building materials for new buildings is to design for disassembly (DFD) (Thormark, 2001). DFD is a design method aimed at facilitating the reusing and recycling of materials and components at the end of the building's life (Crowther, 1999). The design concerns the choice of materials, the structure of the building elements and the type of joints and connections. A typical DFD example is the employment of mechanical dry connections rather than chemical ones and, in wider terms, DFD aims at easily separating multi material assemblies and modules at the building's EOL (Guy and Ciarimboli, 2007). Although DFD may require extra inputs of energy during the design and construction phases, the potential recovery of embodied energy in the materials salvaged for reuse and recycle could far surpass it (Gao et al., 2001). Beyond the more demanding designing phase, the main hindrances to deconstruction (i.e. the process of dismantling a building in order to salvage its materials) are the longer time required for disassembly compared to demolition and the perceived higher costs (Rios et al., 2015).

DFD and material selection could be of paramount importance for temporary buildings (Fumeaux and Rey, 2014). The general assumption that the EOL is very far into the future does not hold for these peculiar structures, considering that their service life is generally limited to the duration of the event they were erected for (Arrigoni et al., 2016). Bearing this in mind, the organisers of the Universal Exposition held in Milan (EXPO Milano 2015, Feeding the Planet, Energy for Life) recommended the designers of the temporary pavilions to pay specific attention to the materials selection and to the salvaging of the components for reconstruction (Expo, 2015 S.p.A., 2015b). To investigate the potential benefits of these guidelines and, consequently, of a proper designing phase in terms of life cycle environmental impacts, a full LCA of a temporary pavilion built for EXPO Milano 2015 was performed. Contrary to typical LCA study of buildings, where the EOL stage is either excluded or presumed (Abd Rashid and Yusoff, 2015), the short lifespan of the structure allowed here to assess the whole life cycle impacts, including the end of the first life. An innovative methodology that considers an extension of the service life was applied to understand how distinct end-of-life scenarios could result in different environmental impacts. Given the increasing demand for temporary structures, either for big events or for emergency after natural disasters (Félix et al., 2013), the results of the present study may be used by designers to improve the environmental sustainability of their structures and to avoid the errors detected in the present case study.