Environmental performance of timber constructions located in highly utilised area - Based on realised buildings made of sawn timber or CLT

The purpose of this research is to evaluate the environmental performance of various timber constructions that have been realised within intensively utilised area in recent years. The appraisal is carried out by means of life cycle assessment (LCA) and covers different timber constructions, mainly the multi-storey building. The ultimate goal is to compare their environmental performance to the outcomes of other constructions like reinforced concrete (RC) and steel construction (SC). The environmental burdens caused by constructions are evaluated based on the framework of LCA. First, the material inventory of selected building projects is established. The scope is emphasised on the primary structural elements such as columns, beams, deck, load-bearing wall and roof. Secondary components, facility and decoration are eliminated out of the research boundary. Based on the material inventory, the impact assessment is carried out to preliminarily calculate the embodied outcome of the timber constructions. The environmental implications of structural elements during early life cycle stages are evaluated. Then, the effect of both disposal and material recycling is integrated in the LCA, including reuse or recovery of the structural wooden components. The LCA takes into account different disposal scenarios associated with construction and demolition waste (C&DW). By doing so, the LCA is the so-called 'from cradle to gate' and 'gate to cradle', without consideration upon the using phase. Among numerous environmental indictors, this research quantifies and discusses the energy consumption and global warming potential (GWP) of the timber buildings only. The five-storey timber building located in urban context is a pioneer project in Taiwan. This building applies crosslaminated-timber (CLT) as the primary structural elements and takes over tremendous loading circumstances. It demonstrates not only the engineering feasibility of CLT for architectural design but also the utilising compatibility of wooden house in urban context. The environmental evaluation proofs the ecological efficiency of timber buildings. In addition, this study compares the environmental performance of timber constructions and other materials. Alternative building models made of RC and steel are developed and intended for further LCA. The LCA results demonstrate that timber constructions cause significantly less impacts than RC and SC do. Timber constructions exhibit carbon sequestration effect, which is unique among three materials. Meanwhile, timber constructions consume only about 20% energy of the RC and SC. While possessing similar form and functionality, timber constructions exhibit better eco-efficiency compared to other generally used materials. When the material recycling is taken into account, the life-cycle eco-efficiency of timber structures is further significant. Wooden constructions can be energy-neutral or even energy-productive, depending on the recycling strategies.