Life-cycle analysis in timber construction - Environmental impact and decision-making

Abstract

The construction sector is recognized as a major player in climate change worldwide, requiring a shift towards renewable energy sources and sustainable material use. Timber, as a natural and renewable material, has been increasingly advocated as a replacement for carbon-intensive construction materials such as steel and concrete. The life cycle approaches such as life cycle assessment (LCA) are adopted, to address relevant benefits and obstacles from sustainability perspective. The main objective of this thesis is investigating the environmental performance of timber construction projects from life cycle perspective, to discuss relevant potential and challenges in climate change abatement. The research approach involves (i) an overview of existing LCA implementation on timber construction projects to find the research gap, and (ii) investigation on the selected overarching topics, including both upfront and post-use schemes of timber use in construction.

The overview reveals large variation in the existing literature of LCA, as well as discovers common features. With respect to the large variation found in the overview, the research investigates the potential of using environmental product declarations (EPDs) to reduce the variability of LCA. However, the results show the obvious variation and inconsistency in EPDs for the same timber product. Similar finding is also observed for generic inventory datasets. Nonetheless, applying LCA to assist decision-making during the tendering process, with using EPDs, is explored. The results indicate that setting limits in the bidding document can effectively reduce the variability of LCA, meanwhile improve efficiency and comparability. Thus, consideration of environmental impact at design stage, as a decision rule to optimize design for sustainable construction is explored. The environmental impact is focused on climate change, depicted by CO2-eq. obtained from LCA results. The risk-informed optimization approach is utilized, which is cost-based. This approach is broadened covering environmental aspect, apart from structural safety and cost. A cost function reflects the above-mentioned aspects is developed.

The influence of different end-of-life (post-use scheme) scenarios on the environmental impact of timber, is studied. The focus is wood cascading, addressing the relevant benefits and challenges in prolonging the life of timber and combating climate change. Three aspects are enclosed: technology, environment, and economy. The investigation reveals that policy is anticipated to be the driving force for the reuse of timber, in the Finnish context. Furthermore, it also indicates that, the equilibrium between reuse and energy recovery of timber should be accounted, as timber serves dual roles: material use for carbon storage and incineration for renewable energy, with each choice involving a trade-off.