Tackling uncertainty in life cycle assessments for the built environment: A review

The building and construction sectors contribute around 38% of global energy-related carbon emissions. LCA plays an important role in environmental assessments of products and buildings. In some countries, assessments are now being required as part of the planning submissions for building projects. And existing building environment certifications systems, such as BREEAM and LEED, require a form of carbon assessment. This has increased the demand for manufacturers to produce environmental product declarations (EPDs) to support assessments and design decisions at building scale, whilst also being used for product procurement. LCA results are often presented as deterministic values and uncertainty is often ignored. This is particularly dangerous in the case of comparative LCA where, for example, the intention can be to reduce carbon emissions by selecting a product or design alternative with a lower footprint. This paper reviews the approaches for dealing with uncertainties in LCA in general, and in the specific application of LCA to construction products and buildings. Buildings are complex and representing this in an LCA, which is a model of reality, can be challenging. The largest impact savings are achieved during the early stages of design where uncertainty and variability in design are high. Therefore, addressing and communicating uncertainty here is even more critical. Barriers, such as access to uncertainty information in EPDs and the lack of a consistent uncertainty procedure, are discussed. Recommendations for future improvements include reporting of uncertainty information and data quality assessments in EPDs, accessible digitised EPD information and integration of uncertainty analysis in building LCA software. As in previous reviews, both building carbon assessments and traditional LCA, suggest, there needs to be a great improvement in the transparency and reporting of assumptions and uncertainties. This applies to both products, in the form of EPDs, and building LCA results in academic literature and industry reports.