Accuracy and completeness of embodied energy, EE, analysis is dependent on the method used. This paper demonstrates that by understanding how energy is consumed in each constituent part and manufacturing processes of reinforced concrete, designers can significantly reduce the overall embodied energy (EE) and embodied carbon (EC) of structures. Both EE and EC of products can vary from country to country. Therefore, to accurately estimate these for RC structures, data specific to the country where they are being constructed must be used. This paper presents the assessment of EE and EC in typical reinforced concrete building structures in Ireland. A case study is presented where it is shown that by replacing 50% of ordinary Portland cement (OPC) with ground granulated blastfurnace slag (GGBS) results in reductions of 29% and 36% to the EE and EC of concrete used in a building, respectively.