Analysis of life-cycle boundaries for environmental and economic assessment of building energy refurbishment projects

Despite the standardization of the life-cycle assessment methodology for the construction sector, analysts tend to apply some simplifications in relation to the system boundaries, omitting some of the life-cycle stages. In particular, for building energy refurbishment projects, there is a general focus on the operational stage, linked to the main objective of reducing operational energy use. This paper evaluates the relevance of each life-cycle stage in relation to the overall environmental and economic impact on residential building energy refurbishment projects. The results from the analysis of the refurbishment strategies at a case study in Spain show the relatively minor importance of the transport and end of life stages. The construction process stage is also of relatively minor importance regarding the environmental performance. The product, maintenance and replacement stages are generally of higher importance, particularly for economic evaluation. An extensive sensitivity analysis demonstrates the difficulties of simplifying the life-cycle boundaries, suggesting that potential simplifications should take into account various parameters, including the climate region, building typologies, and expected service life. As an example, the results have shown that for cold climate zones and buildings, where large energy savings from energy refurbishment strategies can be achieved, the other life-cycle phases are less important and, in most cases, represent less than 10% of life-cycle environmental impacts.