Life cycle sustainability assessment modeling of building construction

Abstract

Building industry is one of the most influential economic sectors, which accounts for 10% of the gross domestic product (GDP) globally and 40% of the world energy consumption. To achieve the goal of sustainable development, it is necessary to understand the sustainability performance of building construction in the environmental, the economic and the social aspects. This study quantitatively evaluates impacts of building construction in the three aspects by using the recently developed life cycle sustainability assessment (LCSA) methodology, in which environmental life cycle assessment (ELCA), environmental life cycle costing (ELCC), and social life cycle assessment (S-LCA) are integrated. The scope of this research covers ‘cradle-to-site’ life cycle stages, from raw material extraction to on-site construction.

Three life-cycle models are developed, namely the Environmental Model of Construction (EMoC), the Cost Model of Construction (CMoC), and the Social-impact Model of Construction (SMoC). EMoC is a comprehensive ELCA model that evaluates environmental impacts of building construction by considering eighteen impact categories. CMoC is an ELCC model that provides analyses on construction costs and externalities. SMoC is an innovative S-LCA model being able to quantify social impacts of building construction in thirteen social impact categories. The three models are then integrated into a newly proposed LCSA framework.

In order to select an appropriate LCIA method for EMoC, the differences among existing life cycle impact assessment (LCIA) methods are investigated. It is found that LCIA methods are consistent in global impact categories, while inconsistent in regional impact categories. ‘ReCiPe’ is selected as the LCIA method to be used in EMoC. Midpoint and endpoint approaches of ‘ReCiPe’ can lead to different interpretations. Endpoint approach emphasizes on certain impact categories and can only be used when midpoint results are provided.

A life cycle inventory is established for ready mixed concrete and precast concrete based on site-specific data from concrete batching plant and precast yard. EMoC is employed to compare environmental performance of precast and cast-in-situ construction methods. It is found that adoption of precast concrete can significantly improve environmental performance of building construction. SMoC suggests that adoption of precast concrete can have both negative and positive impacts on local employment.

A case study is conducted to test the model performance. It demonstrates that environmental impacts of ‘cradle-to-site’ construction activities are mostly attributed to the material stage. The external cost due to carbon emission is about 2% of the total construction cost. Environmental-friendly on-site construction practices can significantly improve social performance of building construction.

The major findings of this study are verified through interviews with the local experts in Hong Kong. These validation interviews confirm that the proposed LCSA framework and the developed models contribute to the building industry in Hong Kong. In particular, this study can be used as a supplementary to the building assessment scheme, HK BEAM Plus. Results from this study can improve the understanding of building sustainability.