An Assessment of Building Structural Elements Lifecycle Embodied Energy and CO2 Emissions
|While operational energy is currently the focal point of sustainability building regulations, embodied energy and CO2 emissions will become more significant as operational energy consumption is reduced. Studies suggest that in the near future, embodied energy could account for up to 40% of a building’s lifetime carbon footprint, bearing in mind that construction of energy-efficient buildings is carbon and energy intensive. Unlike operational energy, embodied energy savings have an immediate significant effect on carbon footprint and are independent of human behaviour. As a result, the assessment of embodied energy and CO2 could soon become an integrated phase in the building design process. However, there is a lack of consensus within the construction industry on how to calculate embodied impacts and where to draw system boundaries, which has impeded advancement on the issue.
This research analysed a building’s structural elements lifecycle embodied energy and CO2 emissions, and investigated which stages within building life are the most significant and offer the most opportunities for reduction of embodied impacts. The study focused on initial, recurring and deconstruction embodied energy and CO2, as well as end-of-life energy recovery and CO2 offsetting potential. Apart from material embodied energy, every stage analysed in this study included material or waste transportation, on-site energy consumption, and labour transportation. A simple single-story structure was used as a case study to perform comparative analyses between two structural design alternatives: glue laminated timber panels, and steel frame with infill concrete blocks.
Research showed that material embodied impacts and end-of-life recovery potential are the two most important phases within a building’s lifecycle. Namely, materials accounted for approximately 80% and 90% of total embodied impacts for timber and steel design, respectively. In addition, over 60% of embodied energy could be recovered from timber combustion, and approximately 25% from steel recycling. Some stages, such as material transportation, can play a relatively significant role as well, especially if the design involves low energy materials transported over long distances. Finally, it was concluded that results are extremely sensitive to the use of various sources for embodied energy and CO2 values.
The selection of low-energy materials, and design for deconstruction with high material recovery potential, prove to be essential for sustainable structural design. Nevertheless, standardisation of tools and methodologies is a crucial factor in the advancement of the embodied energy issue, which together with operational energy analysis, will allow design and construction of truly energy efficient buildings.