The role of a building's structure, and of the structural engineer, in achieving sustainability goals is frequently marginalized. Yet it represents a majority of a new building project's material mass and embodied energy, and is responsible for a large portion of its CO2e emissions. It can also play a role in the annual energy usage of a building, both in good ways (i.e. thermal mass) and bad (i.e. thermal bridging). This presentation will look at quantifying the CO2e of conventional structural systems (concrete, steel, masonry, timber), and alternative systems (SIPs, ICFs, strawbale), and what might be done differently, if CO2e reduction was a design parameter. We will then explore a structural system designed for deconstruction (DfD) and how this approach might influence CO2e emissions. Finally, we will identify some structural details which can cause significant thermal bridging, and strategies to reduce or eliminate the energy loss resulting from these conditions.