Elsevier

Energy and Buildings

Volume 47, April 2012, Pages 159-168
Energy and Buildings

Life cycle greenhouse gas emissions and energy analysis of prefabricated reusable building modules

https://doi.org/10.1016/j.enbuild.2011.11.049Get rights and content

Abstract

Prefabrication is one strategy considered to provide improved environmental performance for building construction. However, there is an absence of detailed scientific research or case studies dealing with the potential environmental benefits of prefabrication, particularly the embodied energy savings resulting from waste reduction and the improved efficiency of material usage. This paper aims to quantify the embodied energy of modular prefabricated steel and timber multi-residential buildings in order to determine whether this form of construction provides improved environmental performance over conventional concrete construction methods. Furthermore this paper assesses the potential benefits of reusability of materials, reducing the space required for landfill and need for additional resource requirements.

An eight-storey, 3943 m2 multi-residential building was investigated. It was found that a steel-structured prefabricated system resulted in reduced material consumption of up to 78% by mass compared to conventional concrete construction. However, the prefabricated steel building resulted in a significant increase (∼50%) in embodied energy compared to the concrete building. It was shown that there was significant potential for the reuse of materials in the prefabricated steel building, representing up to an 81% saving in embodied energy and 51% materials saving by mass. This form of construction has the potential to contribute significantly towards improved environmental sustainability in the construction industry.

Highlights

▸ Modular prefabricated steel, timber and conventional concrete buildings were compared. ▸ An eight-storey, 3943 m2 multi-residential building in Melbourne was investigated. ▸ The life cycle greenhouse gas emission and life cycle energy were quantified. ▸ The potential benefits of reusability of materials were quantified and assessed. ▸ The reductions in the space required for landfill were also quantified.

Introduction

The construction and operation of buildings is responsible for significant environmental impacts, predominately through resource consumption, waste production and greenhouse gas emissions. Treloar et al. [1] have shown the importance of considering the life cycle impacts of buildings, as the environmental impacts of initial construction can be just as significant as those associated with their operation. The construction of buildings generates significant quantities of waste, on average up to 10% of the volume of materials used in constructing the building [2]. A large proportion of this waste goes to landfill where, in Australia, 42% of the total solid waste stream is construction and demolition waste [3]. This is contributing to the rapid depletion and inefficient use of our natural resources and energy and resulting in increased pressure on landfill availability.

Numerous strategies have been adopted in an attempt to improve the efficiencies of construction and reduce waste (design for disassembly, lean construction and waste management). By appreciating the principles of handling and using materials on site, attitudes to prevent waste are being developed and the construction process is beginning to be managed more efficiently [4].

Another strategy for reducing construction waste involves the prefabrication of building components which has also been known to reduce construction costs and time. This involves assembling components of the building in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the building is to be located [5], [6]. This practice is in contrast to the more conventional construction practice of transporting the basic materials to the construction site where all assembly is carried out. The prefabrication of buildings has been shown to provide savings in construction waste of up to 52% [7], mainly through the minimisation of off-cuts [8], and can significantly improve the energy, cost and time efficiency of construction.

To reduce life cycle environmental impacts of buildings, their service life should be extended as much as possible [9]. The durability of the structure plays an important role. For example, the structure of commercial buildings in Australia is typically designed to last 100 years; however the average service life of buildings in the Melbourne CBD is closer to 25 years. This figure is based on the observation that most major refurbishments or deconstructions of office buildings in Melbourne happen within the first 20–30 years of the building's life. The life cycle environmental impacts can be significantly reduced if the structural components of a building are designed to be durable and reusable. Innovative design of the structural connections at the initial development stage is extremely important to ensure that the deconstruction/demolition process can take place efficiently to maximise the reusability of building components.

This study aims to quantify the potential life cycle environmental benefits of prefabricated modular buildings in order to determine whether this form of construction provides improved environmental performance over conventional construction methods.

Section snippets

Background

Waste minimisation strategies have been popular for some time in the construction industry. Many studies measure waste from construction sites on the basis of either volume or mass, to gauge the effect on disposal costs [10], [11], [12]. The savings from reducing waste can be best measured in terms of the environment by considering their embodied impacts [13]. For example, embodied energy (i.e. the energy consumed during extraction, processing, manufacturing, and transportation at all stages

Methodology

A multi-residential building has been used as a case study to assess the life cycle energy performance of prefabricated steel and timber constructions. This section outlines the case study building that was analysed and the methods used to assess the life cycle energy requirements associated with both conventional concrete and prefabricated steel and timber construction approaches for this building.

Results and discussion

This section presents the results and discussion of the life cycle energy analysis of the case study building for prefabricated steel and timber, and concrete construction approaches.

Conclusions

This study has assessed the life cycle energy requirements of three forms of construction for a multi-residential building, conventional concrete construction, prefabricated steel construction, and prefabricated timber construction to determine the environmental benefits offered by modularised prefabrications. This comparison used an innovative hybrid embodied energy assessment approach that has never before been used in this manner. The study has shown that the prefabricated steel system

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