Abstract/Summary

Life cycle Assessment (LCA) methods have been gaining interest within the construction industry for assessing environmental sustainability, particularly carbon emissions. Understanding the relative significance of different lifecycle phases is important when making design decisions to reduce carbon emissions. For certain building types, such as offices, embodied carbon represents a significant proportion of whole-life carbon emissions, with some studies suggesting estimates of 50% or more of total emissions. This is not thought to be the case for Supermarkets where operational emissions are claimed to be predominant due to high annual consumption of energy. Crucial to the apparent significance of embodied carbon, relative to the whole lifecycle, are the assumptions made about building serice life. Yet despite their importance to assessment outcomes, a review of the literature shows that many studies provide little justification for these assumptions. Assertions about the relative weighting of different lifecycle phases within the overall carbon footprint are therefore questionable. A new approach to the selection of service life is proposed that uses historic data on the service lives of similar buildings. This helps to identify an appropriate range of service lives for a parametric analysis of embodied carbon. In a study of UK supermarkets, we find that service life can vary from 15 years to over 50 years. Applying the new approach for this range of service lives we show that the proportion of lifecycle carbon due to embodied emissions can more than double, compared to more conventional approaches. For one of the case-study buildings the embodied carbon would be over 55% of the lifecycle carbon emissions for the minimum service life case of 15 years. We conclude that when estimating the whole-life carbon emissions of a building, assumptions about service life are critical, requiring evidence-based justification. The approach presented offers a new way to address this problem. This will lead to improved understanding of the importance of different lifecycle stages and facilitate better informed design decisions in regard to carbon reduction measures. Further work to understand the factors, such as obsolescence and competitor activity that affect the service life of supermarkets in practice is recommended.