The Environmental Potential of Hybrid Load Bearing Systems - A Life Cycle Assessment of a Skanska Residential Reference House

Abstract

Emissions from production activities in the Swedish construction industry accounts for 17 % of national greenhouse gas emissions, making reduction possibilities of large interest and importance. Concerning construction of new buildings large improvements have been made regarding energy efficiency, putting further emphasizes on the production phase. Construction of timber residential buildings is growing internationally and in Sweden. The environmental potential of structural systems in timber is promising, although associated with certain design and production challenges. Therefore, a life cycle assessment looking into the potential of timber and concrete hybrid systems is of interest. The aim of the thesis is to identify viable hybrid solutions and map their environmental potential regarding climate change. A literature review covering relevant LCA methodology and scientific literature was carried out to form a theoretical base for the report. Findings strengthen the case of timber products emitting less greenhouse gases compared to concrete. However, both systems show large future reduction potential. A case study on a concrete reference house was carried out, substituting incrementally more concrete to CLT through five scenarios. A sensitivity analysis covering the potential of downcycling CLT, using cement replacing materials and the impact of different input data and transport distances for CLT was added to the case study. The discussion of the report mainly covers the result and its sensitivity. Further, the relevance of producing residential buildings with very long life spans, challenges constructing hybrid structural systems and important but omitted impact categories are discussed. Suggestion for key success factors going ahead with CLT and hybrid residential buildings are lastly given. The result from the case study show a clear correlation reduced concrete use and GWP reduction. A majority of the total buildings’ weight and emissions can be correlated to eleven material categories. Product development should be focused on these categories. Downcycling of CLT and using cement replacing materials show large potential for both timber and concrete system. Using both approaches for a hybrid structure yield the largest GWP reductions.